Improved breakdown strength and energy density of Al2O3/nano-ZrO2 composite films via enhanced interfacial repairing behavior Ceram. Int. (IF 3.057) Pub Date : 2018-08-19 Mengxin Li, Manwen Yao, Zhen Su, Wenbin Gao, Xi Yao
Taking Al as top electrode, a repairing layer with ultrahigh dielectric strength and resistivity was generated at the interface between sol-gel Al2O3 films and electrodes under the applied electric field. This repairing layer effectively restored the defects on the film surface and improved the dielectric strength. More importantly, it was found that adding ZrO2 nanoparticle into the matrix film could further enhance the dielectric strength, since the ZrO2 nanoparticle is conductive to forming the interfacial repairing layer. The analysis of ac conduction properties showed that the introduction of nano-ZrO2 resulted in a lower potential barrier and a longer hopping distance for ionic migration. In addition, the simulation result indicated that nano-ZrO2 addition induced a local region of high electric field that accelerated ionic migration. As a result of the two factors, the nanocomposite structure of Al2O3/nano-ZrO2 is capable to provide more ions for the formation of interfacial repairing layer. With the stronger repairing behavior, Al2O3/nano-ZrO2 composite films exhibited significantly enhanced breakdown strength of ~576 MV/m and energy density of 14.7 J/cm3, in contrast with 385 MV/m and 5.9 J/cm3 for pure Al2O3 films with Al electrodes.
Porosity Induced Thermoelectric Performance Optimization for Antimony Telluride Ceram. Int. (IF 3.057) Pub Date : 2018-08-19 Yixi Gu, Xiaowei Liu, Shan Huang, Jingjing Guo, Peng Bi, Jing Shi, Wenwen Zheng, Ziyu Wang, Rui Xiong
Sb2Te3 bulks with various porosities are synthesized via applying different pressures and processes. Pores defect variations are demonstrated by positron annihilation spectroscopy measurement. Through tuning sintering temperature and pressure exerted in one step or two steps, pores and interfaces of the materials are tailored, which enhances the Seebeck coefficient, simultaneously maintains high electrical conductivity and remarkably reduces thermal conductivity. A maximum ZT of 1.17 is obtained at 523 K for Sb2Te3 samples compacted in two steps under 10kN, increasing by 54.1% as compared to corresponding sample under 1kN. Lattice thermal conductivity calculation by modified BET model combining with effective medium theory fits with experiments data, revealing porosity manipulation plays a significant role in reducing thermal conductivity.
Structure and photoluminescence of dysprosium doped antimony-magnesium-strontium-oxyfluoroborate glasses Ceram. Int. (IF 3.057) Pub Date : 2018-08-17 S. Farooq, Y. Munikrishna Reddy, R. Padmasuvarna, Venkata Krishnaiah Kummara, C.S. Dwaraka Viswanath, Sk. Mahamuda
Dysprosium (Dy3+)-doped antimony-magnesium-strontium-oxyfluoroborate (B2O3‒MgF2‒SrO‒Sb2O3‒Dy2O3, BMFSrSbD) glasses were synthesized by traditional melt-quenching method. The synthesized samples have been analyzed by X-ray diffraction, optical absorption and fluorescence techniques for deriving various characteristic properties. Emission spectra of Dy3+: samples were exhibit three well resolved emission bands at around 482, 575 and 666 nm which originated from the 4F9/2→6H15/2,4F9/2→6H13/2 and 4F9/2→6H11/2 transitions upon excitation of wavelength at 452 nm. Decay curves of the 4F9/2 level of Dy3+ ion were display mono-exponential at low Dy3+ concentration (0.1 mol%) and deviated to non-exponential behavior at high concentration of Dy3+ ions (≥ 0.5 mol%). Lifetime of the 4F9/2 level was decreased with increase of Dy3+ ions concentration. Chromaticity coordinates (x,y) of Dy3+:BMFSrSbD samples were evaluated and represented in CIE 1931 chromaticity diagram, appear in the whitish-yellow region. The results suggest that these glasses could be utilized as a potential candidate for the development of display devices and lasers at a wavelength of 575 nm.
Fabrication of Super Flux and High Thermal Shock Resistance Ceramic Membrane Support Ceram. Int. (IF 3.057) Pub Date : 2018-08-17 Wenmin Zhang, Kang Guan, Defang Liu, Cheng Peng, Jianqing Wu
Ceramic membranes play an important role in high temperature gas-solid filtration. However, the thermal stability of the ceramic support at high temperatures has always been a problem. In this study, porous fused silica ceramic supports were fabricated with hexagonal boron nitride as a sintering aid. The results shown that hexagonal boron nitride could inhibit the crystallization of fused silica ceramic particles at high temperature and act as a sintering addictive to reduce firing temperature. The obtained supports have an average pore size of 72 μm, an open porosity of 42%, a bending strength of 16.5 MPa, a Weibull modulus of 8.67 and a gas permeability of 4.23×105 m3/(m2 h bar). The bending strength of the support remained 16 MPa after 30 cold-hot cycles, exhibiting high thermal shock resistance. After corrosion in 20 vol% H2SO4 solution for 8 h, the weight and the bending strength of the support were diminished by 0.6% and 24.32%, respectively. So, the ceramic support showed good acid corrosion resistance.
Porosity-controlled multilayer TaC coatings prepared via wet powder process for multi-functional reactor components in GaN crystal growth system Ceram. Int. (IF 3.057) Pub Date : 2018-08-17 Daisuke Nakamura, Keisuke Shigetoh, Taishi Kimura
Multilayer TaC coatings with layers of different porosities, that provide corrosion resistance and controlled wettability against molten metal are prepared via a wet powder process and a subsequent sintering process. A porous TaC top layer with a dense TaC underlayer formed on a graphite substrate is applied as a reactor component. It is found that this layer significantly increases the surface area of a molten Ga source via capillary action due to its high open porosity. It is also demonstrated that this layer enhances the Ga vapor supply rate, and thus the growth rate, during halogen-free vapor-phase epitaxial growth of GaN crystals.
Influence of alkaline oxide on the deformation of ceramic shell mould at high temperatures during investment casting Ceram. Int. (IF 3.057) Pub Date : 2018-08-17 Yameng Wei, Zhigang Lu, Xin Guo
In this investigation, the effect of alkaline oxides such as Na2O and K2O on the deformation of ceramic shell mould was studied at high temperatures. Two groups of ceramic shell mould samples were prepared by impregnating them with a solution of NaOH and KOH of different concentrations. Systematic creep test was conducted under different compression loads at 2 MPa, 4 MPa and 6 MPa using a specially designed creep testing equipment between 1200 and 1350 °C. The obtained results were analyzed based on Norton-Bailey-Arrhenius (NBA) equation. The phase transformation and micromorphology evolution of different samples were analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. From the results it was observed that the activation energy of ceramic shell mould used was about 198 kJ/mol below 1300 °C, whereas it increased to 325 kJ/mol near 1350 °C with a stress exponent of around 1.50 at all the temperatures. Adding Na2O and K2O decreased the activation energy at low temperature and increased it at high temperature. Besides, the stress exponent obviously decreased to nearly 1.00 below 1300 °C indicated the dominance of interface sliding mechanism, which then increased back to 1.30~1.60 at 1350 °C suggesting a combined creeping mechanism. Based on the results of XRD and SEM, it could be noted that during the creeping process the temperature played an important role in changing the interface structure.
A simple energy-saving aqueous synthesis of Bi2Te3 nanocomposites yielding relatively high thermoelectric power factors (FF:HP07) Ceram. Int. (IF 3.057) Pub Date : 2018-08-17 Fei-Hung Lin, Chia-Jyi Liu
We discover a simple scalable (10 g scale for one batch in this study) route of synthesizing Bi2Te3 nanocomposites in aqueous solution with high yield at room temperature without involving any organic chemicals, capping agents, and surfactants. It is conceivable that the formation mechanism involves interaction between elemental Bi and Te, which takes place at a very slow rate and takes about 2 weeks to form Bi2Te3. Heat treatment of Bi2Te3 nanocomposite yields a single phase of Bi2Te3 with the relatively high power factor of 24.2 μW/cm∙K2 at 425 K compared to other solution methods.
Surface Plasmonic effect of Ag enfold ZnO pyramid nanostructured photoanode for enhanced dye sensitized solar cell application Ceram. Int. (IF 3.057) Pub Date : 2018-08-17 V.S. Manikandan, A.K. Palai, Smita Mohanty, Sanjay K Nayak
Influences of pre-forming on preparation of SiC by microwave heating Ceram. Int. (IF 3.057) Pub Date : 2018-08-17 Xinyue Zhang, Bozhen Song, Yuping Zhang, Rizhen He, Qiancheng Gao, Lei Fan, Shengnan Wei, Leiming Chen, Rui Zhang
Silicon carbide (SiC) crystals were synthesized by microwave sintering using coal and tetraethoxysilane (TEOS) as raw materials. A sol-gel method was carried out to coat coal mineral particles with silicon dioxide (SiO2). The mixed raw powders were pre-formed by uniaxial pressing into cylindrical pellets in dimension of ~30×3mm2. The pre-forming pressure was selected at 0 MPa, 1 MPa, 2 MPa, 3 MPa, 4 MPa and 5 MPa respectively, which led to different apparent density of the green pellets. The influence of apparent density of green pellets on microwave heating behavior was investigated. Different microwave thermal effects were analyzed. Techniques of XRD、SEM were carried out to characterize samples. It was found that pre-forming pressure showed crucial influences on microwave thermal effects and electric field (E-field) intensification. No SiC crystal could be formed without pre-forming pressure. Pre-forming pressure might be the prerequisite for synthesis of SiC by microwave heating. Five consecutive and indispensable heating stages including accumulation of residual air, microwave plasma generation, complex chemical reactions, nucleation and grain growth of SiC crystallites could be distinguished for samples under pre-forming pressure. Different pre-forming pressure leads to changes in heating behavior as well as morphologies of SiC crystals. ~4 MPa might be the optimized pre-forming pressure for both microwave plasma effects and E-field intensification.
Study on Non-isothermal Crystallization Kinetics of the BaO-CaO-Al2O3-B2O3-SiO2 Glass for IT-SOFCs sealing Ceram. Int. (IF 3.057) Pub Date : 2018-08-17 Liangguang Liu, Linghong Luo, Leying Wang, Liang Cheng, Xu Xu, Yongzhi Yu, Ying Qin, Yefan Wu
The crystallization ability plays a key role in effecting thermal ability of sealing glass for intermediate temperature-solid oxide fuel cells (IT-SOFCs) to prevent fuel leakage during operation and insulate the cell stack from the external atmosphere. Herein, using differential thermal analysis (DTA) techniques, the growth mode of crystals precipitated in BaO-CaO-Al2O3-B2O3-SiO2 (BCABS) sealing glass through the heat treatment was calculated in terms of non-isothermal crystallization kinetics for the first time. The calculated results showed that the average kinetic exponent n of the glass was approximatively 1, indicating that the crystal nucleuses became to form and further grew with one-dimensional mode from the surface inwards. Scanning electron microscope (SEM) observations clearly revealed that a large number of one-dimensional filamentous crystals have been formed on the interface between the sealing glass and the electrolyte after the heat treatment at 973 K for 100 h, which perfectly coincided with the theoretical calculations, and the glass was well combined with the electrolyte without any visible cracks or peeling at the interface. The one-dimensional growth of hexagonal BaAl2Si2O8 crystals verified by X-ray diffraction (XRD) could effectively decelerate the decrease of thermal expansion coefficient of glass to ensure enhance the thermo-stability of the BCABS sealing glass for IT-SOFC.
Silica aerogels having high flexibility and hydrophobicity prepared by sol-gel method Ceram. Int. (IF 3.057) Pub Date : 2018-08-17 Yue Zhao, Yan Li, Rubing Zhang
Highly flexible and hydrophobic silica aerogels were synthesized using methyltriethoxysilane and polydimethysiloxane as precursors via two-step acid–base catalyzed sol-gel and supercritical drying. The effects of different precursor and catalyst content on mechanical properties, thermal properties, and contact angles of aerogels were investigated. The aerogels prepared here can be compressed to as high as ~50% of original length and recovered back to their original length. The aerogels showed the hydrophobicity with a water contact angle of 145.6° and low thermal conductivity of 0.0338 W/(m·K). Thermal gravimetric analysis shows that the aerogels were thermally stable up to 350 °C. The mechanical and thermal mechanisms of the silica aerogels were also studied. The prepared silica aerogels that were highly flexible, hydrophobic, and lightweight can be applied in thermal insulation of irregular parts, such as pipelines and outdoor attire that are exposed to moist circumstances as well.
High Temperature Electrical Conductivity and Electrochemical Investigation of La2-xSrxCoO4 Nanoparticles for IT-SOFC Cathode Ceram. Int. (IF 3.057) Pub Date : 2018-08-17 T. Ghorbani-Moghadam, A. Kompany, M.M. Bagheri-Mohagheghi, M. Ebrahimizadeh Abrishami
Single-phase Ruddlesden popper of La2-xSrxCoO4 nanopowders with x=0.7, 0.9, 1.1 and 1.3, were successfully synthesized by a modified sol-gel method. Structural stability and morphology of the prepared samples were examined using HT-XRD analysis, FE-SEM and SEM techniques. HT-XRD analysis of the samples, in the range of room temperature to 850 °C, revealed that the structure of all samples was tetragonal. The electrical conductivity measurements, in the range of room temperature to 850 °C, indicated that by increasing the temperature the electrical conductivity mechanism inverts from variable range hopping to the nearest-neighbor hopping of small polarons. In addition, it was found that by increasing Sr concentration the structure of the sintered samples becomes more stable. The electrochemical characterization was carried out using the impedance spectroscopy (EIS) measurements on symmetrical cells at three different temperatures, 650°C, 750°C and 850°C. The area specific polarization resistance (ASR) of La2-xSrxCoO4-CGO-La2-xSrxCoO4 symmetrical cell, in oxygen flow, was obtained about 1.07, 0.35, 0.33 and 0.43 Ωcm2 at 850°C for the samples with x= 0.7, 0.9, 1.1 and x=1.3, respectively. According to our EIS results, the main rate-limiting step for La2-xSrxCoO4 cathode performance is the dissociation process of oxygen at the surface of cathode at 650°C and the charge transfer limiting in the cathode/electrolyte at 750°C and 850°C. Our results showed that the samples with Sr contents of x=0.9 and x=1.1 can be the promising cathodes for IT-SOFC applications.
Structural, Electrical and Ferroelectric Characteristics of Bi(Fe0.9La 0.1)O3 Ceram. Int. (IF 3.057) Pub Date : 2018-08-18 Nripesh Kumar, Alok Shukla, Nitin Kumar, Sushrisangita Sahoo, Sugato Hajra, R N P Choudhary
Nowadays, much attention is paid for the development of lead-free complex or mixed metal oxides, which can be utilized for multi-functional devices. This communication provides the information on synthesis (by mixed oxide route) and physical properties (structural, electrical and ferroelectric) of the polycrystalline sample of Bi(Fe0.9La0.1)O3 Analysis of the phase formation and basic crystal data of the material using X-ray diffraction (XRD) technique shows an orthorhombic symmetry with well-defined cell parameters. It has been shown that a small amount (10%) of La substitution at the Fe site of BiFeO3 suppresses the impurity phase usually observed during phase formation of BiFeO3. The average crystallite size, calculated through applying Scherrer's technique, was found to be 68 nm. For the study of surface morphology (grain size and distribution) of the compound, the scanning electron microscope (SEM) was used. The grains of different dimension were found homogeneously distributed at the entire surface of the sample. The La substitution strongly affects the capacitive (dielectric) and resistive (electrical) characteristics of bismuth ferrite in a wide range of frequency and temperature. The contributions of grains and grain boundaries in the capacitive as well as in the resistive properties of the material at different temperatures and frequencies were studied by means of the impedance spectroscopy technique. This study has provided numerous useful and interesting data which may find potential industrial applications.
3D conductive CNTs anchored with Na2FeSiO4 nanocrystals as a novel cathode material for electrochemical sodium storage Ceram. Int. (IF 3.057) Pub Date : 2018-08-18 Zaiqiang Feng, Mingqi Tang, Zhenwei Yan
Sodium iron silicate (Na2FeSiO4) has been investigated as a novel cathode material for electrochemical sodium storage due to the abundance of Na and Fe resources, good structure stability and high theoretical capacity. Herein, we report a simple strategy for fabricating the 3D CNTs-decorated Na2FeSiO4 microspheres through a facile spray-drying method. Inside the microspheres, the Na2FeSiO4 nanocrystals are anchored on the CNTs, forming the conductive transport pathways for electrons and Na+-ions. This cathode exhibits a high specific capacity of 168.7 mAh g−1 at 0.1 C and also shows excellent cycling performances at high current rates. Therefore, the as-fabricated 3D composite is an advanced electrode for rechargeable sodium-ion batteries.
Chemical Vapour Deposition of ZrN using in situ produced ZrCl4 as a precursor (CH-4:L04) Ceram. Int. (IF 3.057) Pub Date : 2018-08-18 Elisabeth Rauchenwald, Mario Lessiak, Ronald Weissenbacher, Roland Haubner
ZrN is considered a promising material for high performance coatings of various tools, due to its outstanding mechanical properties. To generate ZrN layers, ZrCl4, a precursor, is effortlessly produced by the reaction of metallic Zirconium with HCl under elevated temperature, utilizing H2 as a carrier gas. In a subsequent CVD (Chemical Vapor Deposition) reactor the ZrCl4 reacts with NH3, forming ZrN coatings. By varying the experimental conditions, such as the H2 and NH3 gas flow, as well as addition of N2 to the reaction gas, the influence on coating thickness, surface morphology and crystal structure of the generated coatings was investigated. Furthermore, the effects of various deposition temperatures in addition to positional differences of the hardmetal samples in the coating reactor were explored. Ultimately, the generated samples were analyzed by evaluation of coating thickness, light optical microscopy as well as SEM, EDX and XRD measurements.
Effects of B4C particle size on the microstructures and mechanical properties of hot-pressed B4C‒TiB2 composites Ceram. Int. (IF 3.057) Pub Date : 2018-08-18 Zetan Liu, Xiangong Deng, Jiamao Li, Yaxin Sun, Songlin Ran
Full dense B4C‒30 vol% TiB2 composites were prepared by hot pressing at 2000 oC under 35 MPa from four different starting B4C powders with their medium particle sizes ranging from 0.5 to 35.8 µm. The effects of B4C particle size on the microstructures and mechanical properties of composites were investigated. The results indicated that both B4C and TiB2 grains grew during sintering process, and each kind of grains had a pinning effect on the grain growth of the other. With coarse B4C powders as raw materials, TiB2 grains in obtained B4C‒TiB2 composites tended to grow with the  zone axis parallel to the applied pressure direction, which possibly reinforced the composites. When the particle size of the starting B4C powder was 7.09 µm, the obtained B4C‒TiB2 composite exhibited the optimized mechanical properties including a flexural strength of 754 MPa, a Vicker hardness of 30.01 GPa and a fracture toughness of 5.23 MPa·m1/2, respectively, due to the most homogenous and finest microstructures.
Fabrication and thermoelectric properties of Ga1-xInxSb compounds by solid reaction Ceram. Int. (IF 3.057) Pub Date : 2018-08-18 Shan Yun, Tan Guo, Yanxing Li, Jiadong Zhang, Huaju Li, Jing Chen, Litao Kang, Aibin Huang
III-V compounds with the zinc blende structure possess high carrier mobility and good power factors due to their unique crystal and electronic structure. In this work, In-doped GaSb (Ga1-xInxSb, x = 0, 0.02, 0.05, 0.1, 0.15, 0.2) were fabricated by combining melting method with SPS sintering technique. The microstructure and thermoelectric properties of Ga1-xInxSb compounds were systematically studied. Experimental results indicate that by introducing In into Ga sites, the lattice thermal conductivity has been effectively reduced by substituting Ga with In, resulting in a ZT value increases from 0.01 to 0.17 (600 K) when x = 0.02. However, further increase of In-doping dosage leads to the decrease of power factors, and therefore the decrease of ZT values.
In Vitro Bioactivity, Physical and Mechanical Properties of Carbonated-Fluoroapatite during Mechanochemical Synthesis Ceram. Int. (IF 3.057) Pub Date : 2018-08-18 Rasha A. Youness, Mohammed A. Taha, Medhat Ibrahim
Mechanochemical synthesis method has been used to prepare nanocrystalline B-type carbonated fluoroapatite (B-CFA). Fourier transform infrared (FTIR) spectroscopy along with X-ray diffraction (XRD) technique was carried out to investigate the effect of milling time on the preparation of B-CFA. In vitro bioactivity of FA during synthesis was examined also by FTIR spectroscopy after soaking in simulated body fluid (SBF). Furthermore, the mechanical properties including hardness, fracture toughness, compressive strength, longitudinal modulus, Young's modulus, shear modulus and bulk modulus of the sintered samples, at 1000 and 1200 °C, for different milling times were measured by ultrasonic non-destructive technique. Furthermore, theoretical model is presented for FA according to the formula Ca10(PO4)6F2.18H2O. The QSAR properties including log P, total energy, heat of formation, energy gap, dipole moment, ionization potential, polarizability, molar refractivity and molecular weight were calculated. FTIR and XRD results revealed that single phase B-CFA was successfully formed after 9 h of milling. Moreover, the results also pointed out that the total energy of FA is much more than hydroxyapatite (HA) indicating that the structure of FA is more stable than HA. These results are in agreement with XRD ones for sintered samples where they did not undergo decomposition reflecting its thermal stability.
Formation of magnesium silicate hydrate in the Mg(OH)2-SiO2 suspensions and its influence on the properties of magnesia castables Ceram. Int. (IF 3.057) Pub Date : 2018-08-18 Yu Zhang, Yawei Li, Yajie Dai
Brucite is an alternative magnesium precursor for magnesia castables. The hydration process of brucite-microsilica suspensions at 50 °C was firstly studied to identify the magnesium-silicate-hydrate (M-S-H) formation. The existence of M-S-H was dependent on the characteristics of brucite. The brucite with smaller grain size exhibited higher reactivity and favored the formation of M-S-H. The early strength of magnesia castables with addition of the 1 wt% reactive brucite powder was increased, which was related to the modified microstructure via filling effect of brucite fine particles and the formation of M-S-H. Explosion resistance of castables was improved as well attributed to the enhanced early strength and the M-S-H phase in the presence of reactive brucite. Besides, the facilitated formation of forsterite bonding phase in the brucite containing castables during firing process and the thermal-mechanical strength such as hot modulus of rupture and refractoriness under load were significantly increased.
Enhanced ferroelectric, magnetic and magnetoelectric properties of multiferroic BiFeO3–BaTiO3–LaFeO3 ceramics Ceram. Int. (IF 3.057) Pub Date : 2018-08-18 Min Zhang, Xiaoyan Zhang, Xiwei Qi, Hongen Zhu, Ying Li, Yaohang Gu
A lead–free multiferroic ceramic 0.7BiFeO3–0.3BaTiO3 showed strong ferroelectric and piezoelectric properties, but weak magnetic and magnetoelectric properties. We herein expected that the electrical and magnetic properties of 0.7BiFeO3–0.3BaTiO3 ceramics could be enhanced by introducing LaFeO3. (0.7–x) BiFeO3–0.3BaTiO3–xLaFeO3 (x = 0–0.2) were synthesized by solid-state reaction. All the ceramics formed a perovskite structure, and a morphotropic phase boundary (MPB) between rhombohedral and orthorhombic phases formed at x = 0.025. The ceramics with MPB composition had high unipolar strain (Smax = 0.14%), piezoelectricity (d33 = 223 pC/N, d33⁎ = 350 pm/V), ferroelectricity (Pr = 25.67 mC/cm2) and magnetoelectricity (aME = 466.6 mV/cm·Oe), which can be attributed to addition of La ions. The improved phase angle also demonstrated augmentation of ferroelectricity on the microscopic view. The ferromagnetism was evidently improved after LaFeO3 doping, and the remanent magnetization Mr increased from 0.0207 to 0.0622 emu/g with rising x from 0 to 0.075. In conclusion, with strong magnetoelectric properties, the prepared ceramics may be applicable as promising lead–free multiferroic ceramic materials for novel electronic devices.
Auto-Combustion Synthesis and Electrochemical Studies of La0.6Sr0.4Co0.2 Fe0.8O3-δ – Ce0.8Sm0.1Gd0.1O1.90 Nanocomposite Cathode for Intermediate Temperature Solid Oxide Fuel Cells Ceram. Int. (IF 3.057) Pub Date : 2018-08-18 S. Ajith Kumar, P. Kuppusami, P. Vengatesh
In the present study, a nanocomposite cathode comprising Fe rich La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) based pervoskite semiconductor oxide and Sm-Gd co-doped ceria rich Ce0.8Sm0.1Gd0.1O1.90 (CSGO) in the ratio of 1:1 has been successfully synthesized by a simple glycine nitrate auto combustion method. The structural properties of the two phase nanocomposite were evaluated by X-ray diffraction and Raman spectroscopy. A detailed electrical properties of co-doped LSCF-CSGO nanocomposites have been studied with a comparison of LSCF added with 10 mol.% and 20 mol.% Gd singly doped ceria (LSCF-GDC10 and LSCF-GDC20) nanocomposites as a function of temperature in the range of 673–1073 K at air atmosphere by AC impedance spectroscopy. The total electrical conductivity of the co-doped LSCF-CSGO nanocomposites has been found to be 0.043 S.cm−1 at 973 K which is higher than that of the LSCF composite containing singly doped compositions. The Sm co-doping in GDC phase has effectively helped to reduce the undesired electronic conduction produced in the doped ceria as the electron concentration of LSCF-CSGO was found to be −2.62 ×1015 cm−3 which was lower than the electron concentration of LSCF containing singly doped nanocomposite (LSCF-GDC20, −2 ×1016 cm−3) estimated by Hall-Effect measurement. The activation energy (Ea) of LSCF-CSGO nanocomposite has been found to be 0.05 eV for the oxygen reduction reaction by temperature dependent Arrhenius equation. The improved electrical properties in terms of high ionic conductivity and low activation energy have been achieved through the incorporation of Sm into GDC10 electrolyte phase in LSCF nanocomposite. The combustion synthesis method has also effectively helped to produce microstructure containing large grain size (~6 μm) which is beneficial for enlarging triple phase boundary (TPB) area of cathodes utilized in solid oxide fuel cells (SOFC) operated at reduced/intermediate temperature (673–973 K).
Preparation and investigation of structure, magnetic and dielectric properties of (BaFe11.9Al0.1O19)1-x - (BaTiO3)x bicomponent ceramics Ceram. Int. (IF 3.057) Pub Date : 2018-08-18 S.V. Trukhanov, A.V. Trukhanov, M.M. Salem, E.L. Trukhanova, L.V. Panina, V.G. Kostishyn, M.A. Darwish, An.V. Trukhanov, T.I. Zubar, D.I. Tishkevich, V.A. Sivakov, D.A. Vinnik, S.A. Gudkova, Charanjeet Singh
(BaFe11.9Al0.1O19)1-x - (BaTiO3)x with x = 0, 0.25, 0.5, 0.75 and 1 bicomponent ceramics has been prepared from single-phase compounds of BaFe11.9Al0.1O19 (x=0) (BFO) and BaTiO3 (x=1) (BTO) by a standard ceramic technique. The constituent materials have been chosen considering their perspective ferrimagnetic and ferroelectric properties, respectively for BFO and BTO. Moreover, Ba-hexaferrites are reported to exhibit ferroelectricity at room temperature as well, and the combination of two ferroelectric phases is of interest. Systematic investigations of the structural, magnetic and dielectrical properties versus chemical composition (x) have been performed. The ferrimagnetic phase transition temperature is almost independent of the BTO content, which is determined by intensity of the Fe3+-O2--Fe3+ indirect superexchange interactions in the BFO hexaferrite phase. However, the coercivity of composite samples is lower due to the contribution of the microstructure-dependent shape anisotropy to the total magnetic anisotropy energy. The permittivity vs. temperature behavior confirmed the existence of two ferroelectric phase transitions corresponding to structural phase transitions in BTO at ~ 400 K and BFO at ~ 700 K. It has been observed that the dielectrical properties of composite samples, including the temperatures of the phase transitions, critically depended on concentration x which affects the composite microstructure. This behaviour has been discussed in terms of microstructure analysis and such parameters as the grain size, porosity and density.
Enhanced piezoelectricity and energy storage performances of Fe-doped BNT–BKT–ST thin films Ceram. Int. (IF 3.057) Pub Date : 2018-08-18 Shuanghao Wu, Pan Chen, Jiwei Zhai, Bo Shen, Peng Li, Feng Li
Fe-doping is an effective way to improve physical performances of piezoelectric and ferroelectric materials. Under such circumstances, x mol% (x = 0.0, 1.0, 1.5, 2.5) Fe-doped 0.72Bi0.5Na0.5TiO3–0.18Bi0.5K0.5TiO3–0.10SrTiO3 (BNT–BKT–ST–xFe) thin films were prepared by sol-gel method and the relationships between the content of Fe and electromechanical properties of the films were studied. The BNT–BKT–ST–1.0Fe thin films exhibit the best electromechanical properties, whose Smax/Emax, Wrec, η, Pmax, Prem and εr of are 68.00 pm/V, 20.34 J/cm3, 65.17%, 71.5 μC/cm2, 14.8 μC/cm2, 868 respectively. These results indicate that BNT–BKT–ST–1.0Fe thin films are promising for applications for advanced piezoelectric materials and capacitors with high energy-storage density.
The Effect of Zn and Ni Substitution on Magnetic and Microwave Absorbing Properties of Co2W Hexagonal Ferrites (FG:PO2) Ceram. Int. (IF 3.057) Pub Date : 2018-08-18 Han-Shin Cho, Sung-Soo Kim
The magnetic (static, high-frequency) and microwave absorbing properties of Zn- or Ni-substituted Co2W hexaferrites have been investigated for application in commercial drones and wireless LANs operated at the frequency of 5.8 GHz. Powders with a composition of (BaCo2-xMexFe16O27 (Me=Zn, Ni)) were prepared by calcination at 1250 °C, where the substitution ratio x was varied from 0.0 to 1.5. With the calcined powders, composite specimens were prepared using silicone rubber as a matrix material. Vibrating sample magnetometry measurements indicate that the composite specimens of Zn-substituted Co2W hexaferrite powders exhibited increased saturation magnetization and decreased coercive force. As a result, ferromagnetic resonance occurred in the frequency range below 6 GHz, which is attributed to the decreased crystal anisotropy field on the basal plane. However, with Ni substitution, the complex permeability spectrum showed an increased resonance frequency (12.9 GHz), which is attributed to the increased crystal anisotropy field by changing the easy-axis of magnetization from the basal plane to the c-axis. The specimens with Zn substitution showed superior microwave absorbing properties at C-band frequencies. For the specimen with Zn substitution with x = 1.0, a reflection loss of –35 dB was obtained at 5.8 GHz with a matching thickness of 4 mm.
Sol-Gel Synthesis and characterization of B4C nanopowder Ceram. Int. (IF 3.057) Pub Date : 2018-08-18 Abolhassan Najafi, F. Golestani-Fard, H.R. Rezaie
In this research, the B4C nanopowder was synthesized through sol-gel method. Nanometric size of precursors were controlled through dispersing agents and controlling pH inside the sol. Mixing the ingredients in molecular size was one of the important reasons in decreasing synthesis temperature of boron carbide particles. In order to evaluate product formation mechanism during sol-gel process, TEM, SEM, DTA/TG, BET, XPS, FTIR and DLS analysis methods were employed. DLS analysis revealed that precursor's particles inside the Sol were below 10 nm. FTIR analysis on chemical bonds indicated that the B-O-C bond was formed inside the gel powder. DTA analysis demonstrated that B4 C powder particles were formed at the temperature around 1270 0 C. Superficial investigations illustrated that the specific surface area of the synthesized B4 C particles is equivalent to 154 m2/g, and also the surfaces of these particles were porous. Further, the size of these cavities is in the meso range. Structural images showed that particles were less than 30 nm. These particles morphology were depend on storage time at the heating stage, as with increasing synthesis time the growth mechanism changes while spherical form of particle shapes converts to whisker.
Effect of nano-scale texture pretreatment on wear resistance of WC/Co tools with/without TiAlN coated flank-face in dry turning of green Al2O3 ceramics Ceram. Int. (IF 3.057) Pub Date : 2018-08-18 Yayun Liu, Jianxin Deng, Lili Liu, Wei Wang, Rong Meng, Ran Duan, Dongliang Ge, Xuemu Li
Advanced ceramics after sintering are almost processed by grinding or non-traditional machining. Nevertheless, these methods are limited by complexity of processing efficiency, tool wear and economic effectiveness. So machining green ceramics before sintering is introduced, it is environmentally friendly, efficient and cheap with high removal rate of materials. During dry turning green ceramics, flank-wear of tools and processing quality of compacts are two main elements to evaluate cutting performance of tools. The processing efficiency and economic effectiveness are mainly effected by the cutting performance of tools. In this paper, polished tool, tool with nano-scale textured flank-face, tool with TiAlN coating deposited on polished flank-face, and tool with TiAlN coating deposited on nano-scale textured flank-face were prepared. Effect of nano-scale texture pretreatment on wear-resistance of WC/Co tools with/without TiAlN coated flank-face was studied in turning of green Al2O3 ceramics. Results displayed that nano-scale textures on the flank-face had prominent effects on the enhancement of flank-wear resistance of tools. Relevant mechanisms were explored that nano-scale textures exhibited “derivative cutting” to protect unworn face from abrasion, and nano-scale textures pretreated on the flank-face could enhance the adhesion strength between coating and matrix. These developed tools could also significantly improve the processing quality of machined surfaces.
Characterization of bioactivity behavior and corrosion responses of hydroxyapatite-ZnO nanostructured coating deposited on NiTi shape memory alloy Ceram. Int. (IF 3.057) Pub Date : 2018-08-18 Masoud Sabzi, Sadegh Moeini Far, Saeid Mersagh Dezfuli
In this research, a ceramic combination of Hydroxyapatite and ZnO with a weight ratio of 50:50 was deposited on NiTi shape memory alloy by Electrophoretic Deposition Process (EPD). Deposition of the Hydroxyapatite-ZnO on NiTi alloy was performed by applying 50 volts for 100 seconds. The sintering operation was then conducted for 2 hours in a furnace under an argon atmosphere at 500 °C. In the next step, the morphology and thickness of the coating were studied by Field Emission Scanning Electron Microscopy (FE-SEM). In addition, bioactivity behavior and corrosion resistance of the coating were evaluated using electrochemical tests, and the rate of the Ni ion release has been investigated in Simulated Body Fluids (SBF) solution. The FE-SEM observations on the morphology of the Hydroxyapatite-ZnO ceramic nanostructured coating revealed that a non-crack coating with approximate 135 μm thickness was deposited on the NiTi alloy. The results also showed that the Hydroxyapatite-ZnO nanostructured coating leads to the formation of ion exchange barrier on the NiTi alloy surface which acts well as a barrier to penetrating nickel ions in the body fluid, in such a way that the corrosion resistances of NiTi alloy has been increased significantly in the presence of Hydroxyapatite-ZnO coating. Also, the adhesion strength of the Hydroxyapatite-ZnO ceramic nanostructured coating on NiTi shape memory alloy was highly desirable (about 25.4 ± 0.1 MPa).
Simultaneous co-substitution of Sr2+/Fe3+ in hydroxyapatite nanoparticles for potential biomedical applications Ceram. Int. (IF 3.057) Pub Date : 2018-08-18 Ismat Ullah, Wenchao Li, Shi Lei, Yu Zhang, Wancheng Zhang, Umer Farooq, Shafqat Ullah, Muhammad Wajid Ullah, Xianglin Zhang
In human, strontium (Sr) follows the same physiological pathway as calcium and thus could be used for improving the bioactivity and osteoconductivity of hydroxyapatite (HAp) in bone tissues. Similarly, iron (Fe) can potentially play an important role in bone remodeling due to its magnetic properties. Therefore, the current study was aimed to simultaneously co-substitute Sr2+/Fe3+ in HAp nanoparticles for various potential biomedical applications. The Sr2+/Fe3+ co-substituted HAp nanoparticles were systematically synthesized through sonication-assisted aqueous precipitation method. The as-synthesized nanoparticles were evaluated for different physicochemical and biological properties. X-ray diffraction (XRD) patterns of Sr2+/Fe3+ co-substituted HAp nanoparticles confirmed their phase purity and showed hexagonal-like structure. Scanning electron microscope (SEM) micrographs showed an agglomerated rod-like morphology of HAp nanoparticles which contained pores consisted of small spheroids. The nanoparticles displayed magnetization (Ms) reliance on the loading level of mole % (X=Fe3+) and exhibited tunable porosity and microhardness (Hv) upon heat treatment. The nanoparticles showed less than 5% hemolysis demonstrating high blood compatibility with high in vitro bioactivity performance. The multifunctional properties of synthesized nanoparticles make them a potential candidate for various biomedical applications; including bone grafting and guided bone regeneration, targeted drug delivery, magnetic resonance imaging, and hyperthermia based cancer treatment.
Influence of interface morphology on erosion failure of thermal barrier coatings Ceram. Int. (IF 3.057) Pub Date : 2018-08-18 Q.M. Yu, Q. He, F.L. Ning
The thermal barrier coating system (TBCs) has complex structure and works in severe service environment. Erosion is one of the main factors causing the failure of TBCs. In the present study, the particle erosion process of atmospheric plasma sprayed (APS) thermal barrier coatings at elevated temperature was simulated by the finite element method. The effects of interface morphology on the penetration depth, particle ricochet velocity and interface stress state were studied, and the key parameters such as particle size, initial velocity and erosion position were also considered. The cosine curve with constant wavelength and varying amplitude was used to represent different interface roughness of TBCs. The results show that the interface morphology has little effect on the penetration depth of top coat (TC) and the particle ricochet velocity. The influence of particle erosion position related to the interface morphology is obvious. Basically, the greater the interface roughness is, the more violent the interfacial stress fluctuation is. During the erosion process, the stress in the middle of the interface is significantly higher than that at other positions. These results facilitate understanding of the particle erosion failure mechanism of APS TBCs. The influence of interface morphology should be considered in erosion research.
Ba1-xSrxTiO3 plates: Synthesis through topochemical conversion, piezoelectric and ferroelectric characteristics Ceram. Int. (IF 3.057) Pub Date : 2018-08-18 Marjeta Maček Kržmanc, Hana Uršič, Anton Meden, Romana Cerc Korošec, Danilo Suvorov
ABO3-type perovskite crystallites with symmetrical crystal structures do not show a tendency to grow in the shape of rods and plates, which are of great scientific interest due to their anisotropic physical properties. A topochemical transformation is one of the most convenient approaches for the preparation of such defined-shape perovskite particles, the functional properties of which can be additionally tailored by the formation of solid solutions. In this study a one-step topochemical conversion reaction from a Bi4Ti3O12 template to A-site-substituted complex Ba1-xSrxTiO3 perovskite microplates was investigated in order to understand the mechanism and to determine the compositional, structural and morphological correlations between the template and the final plate-like particles. Based on our finding that Sr incorporates in a 2.7-times larger amount than expected from the initial composition, the plates with an arbitrary Ba1-xSrxTiO3 solid-solution composition could be prepared using this topochemical transformation. The tetragonal distortion of the Ba1-xSrxTiO3 plates, expressed as the c/a ratio, was found to decrease linearly from 1.0092 (x=0) to 1.0037 (x=0.23), while the compositions with higher x were cubic (c/a=1). According to a piezo-response force microscope (PFM) examination, Ba1-xSrxTiO3 plates with 0≤x≤0.175 showed ferroelectric and piezoelectric characteristics. The temperature of the ferroelectric-to-paraelectric phase transition, as determined by differential scanning calorimetry (DSC), linearly decreased from 124°C (x=0) to 88°C (x=0.11). XRD examinations revealed a strong (001) preferential orientation for the plates (0≤x≤0.11) and the typical (001)/(100) peak splitting indicated the presence of c- and a-domains. The successful preparation and design of Ba1-xSrxTiO3 plates increase the potential of this topochemical transformation for the preparation of plates with a variety of solid-solution compositions and controlled characteristics.
Superconducting properties of a new oxysulfate superconductor Ceram. Int. (IF 3.057) Pub Date : 2018-08-18 H.K. Lee, J. Kim
We report the effects of thermal treatment and La doping on the Sr site in the newly discovered intergrowth superconductor TlSr4Cu2Oz(SO4), whose zero-resistivity temperature is found to be above 70 K. This new phase crystallizes in the tetragonal system (p4/mmm, a = 3.83 Å, c =16.6 Å). Resistivity and room-temperature thermoelectric measurements for the TlSr4Cu2Oz(SO4) samples heat-treated at temperatures below 500 ℃ in Ar atmosphere suggest that the as-prepared sample is under a nearly optimal hole-doped state. In the Tl(Sr4-xLax)Cu2Oz(SO4) ( x = 0 – 1.0) system, superconductivity is suppressed as the La doping content increases, and the decrease in transition temperature with the increase in La doping content above 0.1 is accompanied by increased formation of the TlSr2CuOz phase and decomposition of the TlSr4Cu2Oz(SO4) phase, suggesting that the formation of the TlSr4Cu2Oz(SO4) phase is strongly affected by La doping on the Sr site compared with that of the TlSr2CuOz phase.
Laser Ablation Behavior of Flake Graphite and SiO2 Particle-filled Hyperbranched Polycarbosilane Matrix Composite Coatings Ceram. Int. (IF 3.057) Pub Date : 2018-08-18 Chen Ma, Zhuang Ma, Lihong Gao, Yanbo Liu, Taotao Wu, Yongxiang Zhu, Fuchi Wang
Composite coatings consisting of flake graphite and SiO2 fillers in a hyperbranched polycarbosilane (HBPCS) matrix were designed and prepared to meet the requirements of laser protection. The laser ablation behavior of the composite coatings were investigated. Control experiments were designed to study the performance of SiO2 during laser irradiation. The results show that the introduction of SiO2 changes the anti-laser protective mechanism and can improve the anti-laser property of the coating. High power laser irradiation results in pyrolysis of HBPCS and the formation of SiC particles. Chemical reactions between SiO2, graphite, and SiC play an important role in consuming energy, and provide an excellent cooling effect to the substrate, leading to decreased temperature. SiC particles formed on the surface of the laser ablation area act as a shield to prevent the laser from irradiating deeper layers of the coating. Due to the cooling effect and thermal stability of SiC, the proposed coating shows a good anti-laser property.
A Eu and Tb Co-Doped MOF-5 Compound for Ratiometric High Temperature Sensing Ceram. Int. (IF 3.057) Pub Date : 2018-08-18 Chao Xia, Caiyan Yu, Mengmeng Cao, Jinfeng Xia, Danyu Jiang, Guohong Zhou, Dafeng Zhang, Huili Li
In this work, a new Eu and Tb co-doped luminescent compound based on MOF-5, [Zn4O(BDC)3], (named as compound 1) was successfully synthesized. The structure and morphology characterizations demonstrate that the initial framework of MOF-5 is retained well after co-doping Eu and Tb. The systematic investigations of photoluminescence behaviours reveal that the heat-treated compound 1 (called as compound 1a) can be utilized as a multi-channel readout luminescent thermometer in emission intensity ratio, decay time ratio, and luminescence color. It simultaneously exhibits the excellent repetitiveness and reversibility under high temperature region from 303 to 473 K. The relative sensitivity of 1.8%/K at 473 K is much higher than the best one of 1.19%/K previously reported for the mixed-lanthanide MOF Tb0.8Eu0.2BPDA. Untill now, such a ratiometric luminescent thermometer with a high sensitivity at the temperature as high as 473 K has been rarely explored.
Spinodal decomposition in the Ta-Mo-Al-N films activated by Mo incorporation: toward enhanced hardness and toughness Ceram. Int. (IF 3.057) Pub Date : 2018-08-18 Jun Hao, Yidan Zhang, Ping Ren, Kan Zhang, Jianhong Chen, Suxuan Du, Meijia Wang, Mao Wen
Spinodal decomposition in the transition metal aluminum nitrides, usually triggered by annealing, can enhance hardness via forming coherent nanometer-size domains, but it is still required to activate during fabrication. Herein, Mo was introduced into Ta-Al-N to obtain Ta-Mo-Al-N films by co-sputtering method, which induced two kinds of phase separations, including ~15 at. % Mo induced presence of stable wurtzite AlN phase and ~28 at. % Mo activated spinodal decomposition forming coherent fcc-Ta-Al-N and Mo-Al-N nano-domains. It is found that both hardness and toughness would be worsened by presence of hexagonal wurtzite AlN phase at incorporation of ~15 at. % Mo. On the contrary, once spinodal decomposition took place at ~28 at. % Mo, achieving the joint targets of enhanced hardness and toughness, together with reduced friction and improved wear-resistance. It may provide a new strategy to activate spinodal decomposition during fabrication by alloying additional elements.
A duplex coating composed of electrophoretic deposited graphene oxide inner-layer and electrodeposited graphene oxide/Mg substituted hydroxyapatite outer-layer on carbon/carbon composites for biomedical application Ceram. Int. (IF 3.057) Pub Date : 2018-08-17 Leilei Zhang, Feiyan Zhu, Hejun Li, Fei Zhao, Shaoxian Li
A duplex coating composed of electrophoretic deposited graphene oxide (GO) inner-layer and electrodeposited GO/Mg substituted hydroxyapatite (MH) outer-layer was prepared on carbon/carbon composites (CC). The morphology and microstructure of GO-GO/MH coating were researched by Scanning electron microscopy, energy dispersive X-ray spectroscopy, X-ray diffraction, Raman spectroscopy and X-ray photoelectron spectroscopy. The bonding strength between GO-GO/MH coating and CC substrate was investigated by shear test. The in-vitro bioactivity of GO-GO/MH coating was analyzed by simulated body fluid (SBF) immersion test. The results demonstrated that electrophoretic deposited GO inner-layer was successfully introduced on CC and could serve as an interlayer between CC and following electrodeposited GO/MH outer-layer. GO/MH outer-layer presented a flake morphology with 150–250 nm in thickness and 1.5–2.5 μm in width, exhibiting porous three-dimensional networks structure uniformly. The shear test showed that the bonding strength between the duplex coating and CC reached 7.4 MPa, which was 80.49% higher than that of single-layered MH coating without GO. The duplex coating could induce the formation of flocculent and chapped apatite after SBF immersion, which demonstrated the in-vitro bioactivity of the duplex coating. These results suggested that GO-GO/MH coating might be a promising candidate in the field of biomaterials, especially for implant coatings.
Improving photoelectric performance of MoS2 photoelectrodes by annealing Ceram. Int. (IF 3.057) Pub Date : 2018-08-17 Keyu Si, Jingyao Ma, Yaohui Guo, Yixuan Zhou, Chunhui Lu, Xiang Xu, Xinlong Xu
Semiconductor photoelectrochemistry (PEC) technology has attracted wide interest as it not only reveals the photoelectric properties of advanced materials, but also promotes energy conversion from the sunlight based on these materials. Herein, we investigated photoelectric properties of annealed and unannealed liquid phase exfoliated few-layer molybdenum disulfide (MoS2) photoelectrodes by PEC measurement. The linear sweep voltammograms and photoelectric response I-t curves demonstrate enhanced performance of MoS2 films after annealing. Nyquist impedance and Bode phase plots demonstrate a higher charge transfer property and a longer charge lifetime after annealing. The enhancement due to annealing could come from the increase of the crystalline and compact density of MoS2 nano-sheets, which is proved by X-ray diffraction and Raman spectroscopy in line with the absorption spectroscopy. Our results pave the way for the improvement of two-dimensional material based photoanodes for high performance of PEC applications by a simple method.
Design and fabrication of whisker hybrid ceramic membranes with narrow pore size distribution and high permeability via co-sintering process Ceram. Int. (IF 3.057) Pub Date : 2018-08-17 Dong Zou, Xuebin Ke, Minghui Qiu, Xianfu Chen, Yiqun Fan
Ceramic microfiltration membranes (MF) with narrow pore size distribution and high permeability are widely used for the preparation of ceramic ultrafiltration membranes (UF) and in wastewater treatment. In this work, a whisker hybrid ceramic membrane (WHCM) consisting of a whisker layer and an alumina layer was designed to achieve high permeability and narrow pore size distribution based on the relative resistance obtained using the Hagen-Poiseuille and Darcy equations. The whisker layer was designed to prevent the penetration of alumina particles into the support and ensure a high porosity of the membrane, while the alumina layer provided a smooth surface and narrow pore size distribution. Mass transfer resistance is critical to reduce the effect of the membrane layers. It was found that the resistance of the WHCM depended largely on the alumina layer. The effect of the support and whisker layer on the resistance of the WHCM was negligible. This was consistent with theoretical calculations. The WHCM was co-sintered at 1000 °C, which resulted in a high permeability of ~645 Lm−1h−1bar−1 and a narrow pore size distribution of ~100 nm. Co-sintering was carried out on a macroporous ceramic support (just needed one sintering process), which greatly reduced the preparation cost and time. The WHCM (as the sub-layer) also showed a great potential to be used for the fabrication of ceramic UF membranes with high repeatability. Hence, this study provides an efficient approach for the fabrication of advanced ceramic MF membranes on macroporous supports, allowing for rapid prototyping with scale-up capability.
Novel Synthesis and Antimicrobial Studies of Nanoscale Titania Particles Ceram. Int. (IF 3.057) Pub Date : 2018-08-17 Aneela Anwar, Samina Akbar, Mohsin Kazmi, Ayesha Sadiqa, Syeda Rubina Gilani
In the present investigation, a novel strategy of continuous microwave assisted flow synthesis (CMFS) has been adopted in comparison to traditional synthesis procedures (sol-gel and chemical precipitation method) for the quick production of TiO2 nanoparticles with very fine particle properties. The X-ray powder diffraction analysis (XRPD) and transmission electron microscopy (TEM) were two techniques used for analysing the properties related to structure and particle morphology of the resultant samples. It was observed that the particles formed by using continuous flow route were less agglomerated, and particle size (~6 nm) was smaller in comparison with others obtained using sol-gel (~9 nm) and chemical precipitation method (~15 nm). X-ray diffraction impressions established the generation of Anatase phase with preferential  dimension. Zeta potential computations were taken to inspect the colloidal stability of nanoparticles. Antimicrobial nature of TiO2 nano-samples was analyzed by using various bacterial and fungal strains. The nanostructured TiO2 particles confirmed outstanding uniformity with respect to chemical and structure. This new ceramic substance with strong antimicrobial activity promised magnificent potential in bone tissue engineering.
TEM characterization of a Supra-Nano-Dual-Phase binder phase in spark plasma sintered TiB2–5wt%HEAs cermet Ceram. Int. (IF 3.057) Pub Date : 2018-08-17 Yulin Li, Haiyue Xu, Boren Ke, Yuchen Sun, Kai Yang, Wei Ji, Weimin Wang, Zhengyi Fu
In our previous work, titanium diboride (TiB2) with high relative density and excellent mechanical properties has been synthesized by spark plasma sintering (SPS) with CoCrFeNiAl high-entropy alloys (HEAs) as sintering aid. This present work mainly focuses on the detailed morphology and elemental distribution in the TiB2–5wt%HEAs cermet by transmission electron microscopy (TEM) with energy dispersive spectrometer (EDS) mapping analysis. The characterization of the HEAs binder phase proves a so-called “Supra-Nano-Dual-Phase (SNDP)” structure, which has near-ideal strength at room temperature. Therefore the high strength of the SNDP binder phase leads to the excellent mechanical properties of the TiB2–5wt%HEAs cermet.
Observation of low- and high-temperature CuFe2O4 phase at 1100°C: the influence of Fe3+ ions on CuFe2O4 structural transformation Ceram. Int. (IF 3.057) Pub Date : 2018-08-16 Violeta N. Nikolić, Milica Vasić, Mirjana M. Milić
Samples containing CuFe2O4 and CuO nanoparticles were synthesized by coprecipitation method and subjected to thermal treatment at 300 °C, 500 °C, 700 °C, 900 °C and 1100 °C. Depending on the synthesis conditions, high-temperature treatment of the prepared samples brought to the formation of CuFe2O4 with a tetragonal or cubic structure, which was confirmed by X-ray diffraction analysis. The influence of formation mechanism onto the crystallite sizes of nanoparticles and structural transformation of CuFe2O4 is discussed. For the first time it was shown that variations of the initial amount of Fe3+and Cu2+ ions precursors resulted in the formation of low- and high-temperature CuFe2O4 phase at the same annealing temperature, 1100 °C.
Significantly enhanced dielectric permittivity and suppressed dielectric loss in Na1/2Bi1/2Cu3Ti4O12/poly(vinylidene fluoride) nanocomposites Ceram. Int. (IF 3.057) Pub Date : 2018-08-16 Wattana Tuichai, Supamas Danwittayakul, Prasit Thongbai
We report significantly enhanced dielectric permittivity and suppressed dielectric loss in Na1/2Bi1/2Cu3Ti4O12/poly(vinylidene fluoride) (NBCTO/PVDF) nanocomposites. NBCTO nanoparticles (≈100 nm) synthesized via a chemical combustion method were used as a filler to enhance the dielectric permittivity of PVDF polymer. NBCTO/PVDF nanocomposites with various volume fractions of NBCTO were fabricated using conventional mixed powders and hot pressing. Microstructural analysis revealed good dispersion of NBCTO nanoparticles in the PVDF matrix compared to that of NBCTO micro-particles. The dielectric permittivity of NBCTO/PVDF nanocomposites increased with increasing NBCTO filler content. Interestingly, at 103 Hz, the nanocomposite with 50 vol.% of NBCTO exhibited a largely enhanced dielectric permittivity of about 261 and a low dielectric loss of 0.4. Greatly increased dielectric permittivity in the NBCTO/PVDF nanocomposites can be ascribed to large interfacial spaces and short interparticle distances.
Integrated passive wireless pressure and temperature dual-parameter sensor based on LTCC technology Ceram. Int. (IF 3.057) Pub Date : 2018-08-16 Lin Lin, Mingsheng Ma, Faqiang Zhang, Feng Liu, Zhifu Liu, Yongxiang Li
This paper presents a kind of passive wireless pressure and temperature integrated inductor-capacitor (LC) resonant sensor based on low temperature co-fired ceramic (LTCC) technology. The pressure sensing part is dependent on a traditional cavity capacitor. The temperature sensing part is composed of an interdigital capacitor and a planar spiral inductor. The capacitance and the resistance of inductor coil would change as a response to temperature. The LTCC material with a low Young's modulus of ~65 GPa prepared by our laboratory was used to obtain high pressure sensitivity. The experimental results showed that the prepared sensor has a pressure sensitivity of 1.16 kHz/kPa, and a temperature sensitivity of 0.062% dB/°C within the range of 140–850 kPa, 50–500 °C, respectively.
Preparation and functional characterization of magnetoelectric Ba(Ti1-xFex)O3-x/2 ceramics. Application for a miniaturized resonator antenna Ceram. Int. (IF 3.057) Pub Date : 2018-08-16 Felicia Gheorghiu, Cristina Elena Ciomaga, Mantas Simenas, Mirela Airimioaei, Shan Qiao, Sorin Tascu, Vidmantas Kalendra, Juras Banys, Ovidiu G. Avadanei, Liliana Mitoseriu
Diluted magnetic oxides attracted a great interest in the last years as materials for spintronics and magnetoelectric devices. We propose in the present paper such a magnetoelectric ceramic system for an application as miniaturized resonator antenna in GHz range. BaTi1-xFexO3-x/2 (0≤x≤0.02) polycrystalline ceramics have been produced by solid state reaction. X-ray diffraction analysis and Rietveld refinement have shown that Fe doping of BaTiO3 lattice produces a transition from tetragonal crystalline symmetry (for x≤0.01) to a superposition of tetragonal and hexagonal phases for the compositions x=0.015 and 0.02. As result of Fe addition, the Curie temperature of BaTi1-xFexO3-x/2 ceramics exhibit a shift from 127°C towards lower values and reaches 85°C for x=0.02. A competition between weak ferromagnetic and antiferromagnetic character as a function of composition and temperature is determined both by the presence of transition metal ion and of the oxygen vacancies. Due to its electromagnetic properties, an optimized composition x=0.01 was used for producing a miniaturized antenna which was found to show a frequency dependent S11 response similar to the simulated one.
Enhanced Photocatalytic Activity of g-C3N4 2D Nanosheets through Thermal Exfoliation Using Dicyandiamide as Precursor Ceram. Int. (IF 3.057) Pub Date : 2018-08-15 Lirong Yang, Xiaoyu Liu, Zhigang Liu, Chunmei Wang, Gang Liu, Qinglong Li, Xiaoxin Feng
g-C3N4 has received extensive attention because of its good chemical stability and environmental friendliness. Since g-C3N4 prepared from various precursors had different photocatalytic activities, g-C3N4 materials marked as U-gCN, D-gCN and M-gCN were synthesized from various precursors of urea, dicyandiamide and melamine, respectively. The D-gCN and M-gCN with smaller surface area were heated again to obtain exfoliated g-C3N4 with 2D nanosheet morphology and larger specific surface area named D-gCN-L and M-gCN-L, respectively. The synthesized bulk g-C3N4 and g-C3N4 2D nanosheets were characterized by XRD, SEM, BET, PL, UV-Vis diffuse reflectance spectroscopy, XPS, zeta potential and TG. The photocatalytic degradation of methylene blue (MB) was carried out on U-gCN, D-gCN, M-gCN, D-gCN-L and M-gCN-L, and D-gCN-L shows the highest photocatalytic degradation performance because of its larger specific surface area, lower electron-hole recombination and wide light absorption range.
High electromechanical strain properties by the existence of nonergodicity in LiNbO3‒modified Bi1/2Na1/2TiO3‒SrTiO3 relaxor ceramics Ceram. Int. (IF 3.057) Pub Date : 2018-08-15 Young-Hwan Hong, Hyoung-Su Han, Gwang-Hwi Jeong, Young-Seok Park, Thi Hinh Dinh, Chang Won Ahn, Jae-Shin Lee
This study investigated the effect of LiNbO3 modification on the dielectric, ferroelectric and electromechanical strain properties of Bi1/2Na1/2TiO3‒SrTiO3 (BNT‒ST) lead‒free relaxor ceramics. The sintering temperature for lead‒free BNT‒ST relaxor ceramics was slightly decreased from 1175 °C to 1050 °C by modifying with LiNbO3. We found that the sintering temperature affects the dielectric behavior of 0.76BNT‒(0.24‒x)ST‒xLiNbO3 (BNST‒100xLN) ceramics at high temperature (near dielectric maximum temperature, Tm). The Tm for the low‒temperature sintered sample was shifted to relatively higher temperature by comparison with the high‒temperature sintered samples. Furthermore, the degradation of dielectric behavior near Tm in low‒temperature sintered BNST‒2LN ceramics was revealed after poling treatment and seem to be related to the existence of a high temperature stabilized nonergodic relaxor phase. Accordingly, we assume that the stabilized nonergodic relaxor phase is responsible for the relatively late transition from ferroelectrics to the relaxor. Therefore, we obtained the improved d33⁎ of 616 pm/V as the highest value in low‒temperature sintered BNST‒2LN ceramics.
Olive mill wastewaters decontamination based on organo-nano-clay composites Ceram. Int. (IF 3.057) Pub Date : 2018-08-15 Luciana Sciascia, Selene Casella, Giuseppe Cavallaro, Giuseppe Lazzara, Stefana Milioto, Francesco Princivalle, Filippo Parisi
Green composites for environmental applications were successfully prepared by intercalation of the biosurfactant Quillaja saponin onto montmorillonite mineral clay on varying pH and surfactant/clay ratio. Equilibrium adsorption isotherms were constructed and the system was characterized by performing TGA and XRD analyses. The efficiency of the surfactant-modified clay in the removal of the organic content present in olive mill wastewaters (OMW) was evaluated by means of spectrophotometric measurements. The interest for this cogent issue comes from the consideration that, despite their high pollutant content, OMW can be considered as a potential resource of several organic compounds which can be recovered for a wide array of pharmaceutical and industrial applications. Two different strategies were proposed. In the first one, dried surfactant/clay hybrids were added to the batch samples under continuous stirring, while in the second alternative approach the organoclays were packed in chromatography column filled with multiple alternate layers of sand and organoclay. These studies revealed the efficacy of the methods used and suggested that the modification of the montmorillonite clay substrate significantly improves the performance of the clay.
In-situ synthesis and densification of boron carbide and boron carbide-graphene nanoplatelet composite by reactive spark plasma sintering Ceram. Int. (IF 3.057) Pub Date : 2018-08-14 Rajath Alexander, T.S.R. Ch. Murthy, K. Vasanthakumar, N.S. Karthiselva, Srinivasa Rao Bakshi, Kinshuk Dasgupta
Simultaneous synthesis and densification of boron carbide and boron carbide- graphene nano platelets (GNP) were carried out by reactive spark plasma sintering of amorphous boron and graphene nano platelets at temperature ranging from 1200 to 1600°C, pressure of 50 MPa and heating rate of 50 °C/min and 100 °C/min. X-ray diffraction and Raman spectroscopy confirmed the formation of required phases. Electron microscopic images revealed the formation of sub-micron and nano sized grains of plate like morphology. Sintered product with high relative density of 96%TD was achieved at a temperature of 1600°C and heating rate of 50 °C/min for B4C stoichiometric composition and also exhibited maximum hardness of 21.10 GPa.
Sintering Paths and Mechanisms of Pure MgAl2O4 Conventionally and Microwave Sintered Ceram. Int. (IF 3.057) Pub Date : 2018-08-14 Rodolphe Macaigne, Sylvain Marinel, Dominique Goeuriot, Sébastien Saunier
In this paper, a comparative study between conventional and microwave sintering of pure spinel MgAl2O4 is presented. The goal is to clarify and identify the possible microwave effects on densification and microstructure of the pure spinel. Sintering trajectories obtained for microwave and conventional sintering are similar and converge into a unique trajectory. Therefore, microwave processing does not refine the grain size of pure spinel. The dominant mechanism of initial and intermediate stages of sintering was determined from the shrinkage curves and sintering trajectory. It was shown that densification is mostly controlled by grain boundary diffusion for both processes. Porosity of microwave and conventionally sintered samples was also characterized by mercury porosimetry and BET analysis. The evolution of the open porosity and pore size distribution is the same whatsoever the process used. This work shows that microwave sintering does not differ that much from conventional sintering on pure MgAl2O4 material.
Novel nano-dimensional cubic-spherical morphology for (Y2O3)0.5-(MgO)0.5 nanocomposite: Synthesis and optical properties Ceram. Int. (IF 3.057) Pub Date : 2018-08-15 S.H. Vaez, M.R. Loghman-Estarki, R.Shoja Razavi, A. Alhaji, Ajay Kumar Mishra
New cubic-spherical morphology was obtained for (Y2O3)0.5-(MgO)0.5 nanocomposite by the polymeric complex method. In this method, magnesium acetate, yttrium nitrate and C10H16N2O8 (EDTA) were used as a source of Mg2+, Y3+ and both template and chelate agent, respectively. Results show that with increasing pH value from 2 to 8, the morphology of the sample was changed from irregular to the mixture of cubic and spherical particles. Furthermore, according to the PL results, the nanopowder had the strong emission peak centered at 348 nm and 450 nm, corresponding to the electronic transition of T 1 u 1 → A 1 g 2 and B 1 u 3 → A g 1 , respectively. The narrow blue, orange, and red bands are also located in the 450 nm, 580 nm and 690 nm spectral ranges.
Dazzling cool white light emission from Ce3+/Sm3+ activated LBZ glasses for W-LED applications Ceram. Int. (IF 3.057) Pub Date : 2018-08-15 L. Vijayalakshmi, K. Naveen Kumar, Pyung Hwang
We synthesized a batch of co-doped (Ce3++Sm3+): LBZ glass specimens by melt quenching process and their structural and radiation properties were studied by employing XRD, FE-SEM, optical absorption, photoluminescence and lifetime measurements. UV-Vis-NIR absorption studies of the co-doped (Ce3++Sm3+): LBZ glassy matrix displays pertinent bands of both Ce3+ and Sm3+ ions. Individually doped Sm3+: LBZ glass exhibit bright orange emission at 603 nm (4G5/2 → 6H7/2) under the excitation of 403 nm. Nevertheless, the luminescence intensities pertaining to Sm3+ were extraordinarily increased by co-doping with Ce3+ ions to Sm3+: LBZ glassy matrices because of energy transfer from Ce3+ to Sm3+. The fluorescence spectra of co-doped (Ce3++Sm3+): LBZ exhibits characteristic emission bands of Ce3+ (441 nm, blue) and Sm3+ (603 nm, reddish orange) under the excitation of 362 nm. Decay curves of Ce3+ and Sm3+ ions in co-doped glass has been fitted to double exponential nature. The decreasing lifetime of donor ion and rising lifetime of acceptor ion in double doped glass could support the energy transfer from Ce3+ to Sm3+ ions in the host matrix. The CIE coordinates and CCT values were calculated for all the obtained co-doped glassy samples from their luminescence spectra. By adding Ce3+ ions to individually doped Sm3+: LBZ glass matrix, the emitting color changes from reddish orange to white light which resembles the energy transfer from Ce3+ to Sm3+ ions. These studies, perhaps implied that attained co-doped (Ce3++Sm3+): LBZ glassy samples are potential materials for white lighting appliances.
Deposition and characterization of epitaxial Ta-doped TiO2 films for ultraviolet photoelectric detectors Ceram. Int. (IF 3.057) Pub Date : 2018-08-15 Wei Zhao, Linan He, Xianjin Feng, Hongdi Xiao, Caina Luan, Jin Ma
Undoped and tantalum-doped titania (TiO2:Ta) films were synthesized via metalorganic chemical vapor deposition (MOCVD). The crystallization qualities, surface morphologies and optical properties of the deposited films were systematically characterized. The results indicated that the films having low doping levels were epitaxial anatase titania along  orientation with high transparency in visible region. The optical band gap could be modulated from 3.38 to 3.52 eV by controlling Ta doping levels. Ultraviolet (UV) photoelectric detectors with metal-semiconductor-metal (MSM) structure were designed and fabricated based on the undoped and Ta-doped films. The maximum spectral response of 32.3 A/W was detected at about 315 nm for the 1% Ta-doped TiO2 film-based detector. The detectors based on the undoped and 1% Ta-doped TiO2 films also presented good temporal responses and visible-blind characteristics, showing excellent UV light detection performances.
Physical properties and electrochemical performance of Zn-substituted Na 0.44 Mn 1 − x Zn x O 2 nanostructures as cathode in Na-ion batteries Ceram. Int. (IF 3.057) Pub Date : 2018-08-15 Mahesh Chandra, Rishabh Shukla, Rakesh Saroha, A.K. Panwar, Amit Gupta, S. Basu, R.S. Dhaka
We report the synthesis, physical properties and electrochemical performance of Zn substituted Na 0.44 Mn 1 − x Zn x O 2 ( x = 0 – 0.02) nanostructures as cathode in Na-ion batteries for energy storage applications. These samples stabilize in the orthorhombic structure and the morphology is found to be slab like with 100 – 200 nm width and few micrometer of length. The resistivity measurements show highly insulating nature for all the samples, where the activation energy decreases with increasing Zn concentration indicating more defect levels in the band gap. The cyclic voltammogram (CV) shows reversible oxidation and reduction peaks, which clearly shift towards higher/lower potentials with increasing Zn concentration up to 2%. We observed the specific capacity of about 100 mAh/g at current density of 4 mA/g and improved cycle life for Zn substituted x = 0.005 sample. However, with further increasing the Zn concentration ( x = 0.02 ), the specific capacity decreases, which can be a manifestation of the decreased number of reduction peaks in the CV data.
DFT study of electronic structure and properties of N, Si and Pd-doped carbon nanotubes Ceram. Int. (IF 3.057) Pub Date : 2018-08-15 Cuihua Zhao, Xi Zhou, Shijian Xie, Hongyou Wei, Jianhua Chen, Xujie Chen, Chuanji Chen
The electronic structure and properties of N, Si and Pd-doped (10,0) SWCNTs were studied by DFT method. N, Si and Pd dopings induced great structural modifications of the carbon nanotube walls. The type of SWCNT changes from semiconductor to metal conductor after N doping. The semiconducting property is well maintained for Si- and Pd-doped CNTs, however, the band gaps of Si- and Pd-doped CNTs decrease because of the interaction between doping atoms and nanotubes. The band gap of Pd-doped CNT (0.35 eV) is smaller than that of Si-doped one (0.39 eV). The impurity levels appear along with 2p orbitals of carbon atom, and DOS curves with different dopings change substantially. For N-doped CNT, carbons lose electrons, and nitrogen gains electrons, while carbons gain electrons, silicon and palladium lose electrons for Si- and Pd-doped CNTs. The different electronic structures caused by different dopings result in different properties of CNTs.
Role of the vapour phases in the formation mechanism of 15R-SiAlON in FexSiy-Si3N4-Al2O3 composites at 1800 °C Ceram. Int. (IF 3.057) Pub Date : 2018-08-15 Haixia Qin, Yong Li, Menglong Long, Xi Nie, Peng Jiang, Mingwei Yan, Wendong Xue
The synthesis of 15R-SiAlON in FexSiy-Si3N4-Al2O3 composites was carried out at 1800 °C in flowing nitrogen. The role of the vapour phases from ferrosilicon nitride (FexSiy-Si3N4) and Al2O3 was studied by phase evolution, microstructure, and thermodynamic analyses. The results show that the formation of 15R-SiAlON is highly related to SiO(g), Si(g), Al2O(g) and Al(g) from FexSiy-Si3N4-Al2O3 composites. At 1800 °C in flowing nitrogen, SiO(g) and Si(g) are generated from ferrosilicon nitride. Al2O(g) and Al(g) are released from Al2O3, and their pressures depend on that of oxygen. The increase of ferrosilicon nitride promotes the generation of vapour phases. The diffusion of Al2O(g) and Al(g) into Si3N4, and of SiO(g) and Si(g) into Al2O3 particles enable the growth of 15R-SiAlON flakes based on both the Si3N4 and Al2O3 substrates by solid-gas reaction. In the presence of the Fe-Si liquid, 15R-SiAlON whiskers with Fe-Si sphere on the top are generated by the liquid-solid-gas mechanism. The reactions between Al2O(g)/Al(g) and SiO(g)/Si(g) in nitrogen generate large amounts of 15R-SiAlON whiskers by the gas-gas mechanism.
Effect of sintering temperature and Ho2O3 on the properties of TiO2-based varistors Ceram. Int. (IF 3.057) Pub Date : 2018-08-15 Fengchao Peng, Dachuan Zhu
In this study, a series of TiO2-based ceramics doped with different contents of Ho2O3 in the range of 0~0.6 mol% are prepared by means of a conventional solid-state reaction method. Phase composition, microstructure and element distribution are studied by use of X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) separately. The influence of sintering temperature and Ho2O3 on the properties of samples is explored. The results show that the breakdown voltage decreases continuously while both the nonlinear coefficient and the relative dielectric constant ascend firstly and then descend with the sintering temperature increasing. Meanwhile, the relative dielectric constant and nonlinear coefficient of samples firstly ascend and then descend with the increasing of Ho2O3. Although the minimum breakdown voltage (3.3 V/mm) is obtained when sample is sintered at 1450°C, the sample doped with 0.45 mol% Ho2O3 sintered at 1400°C exhibits high comprehensive electrical properties, with breakdown voltage of 6 V/mm, the nonlinear coefficient of 5.5 and the relative dielectric constant of 1.88×105.
The Effects of La2O3 Doping on the Photosensitivity, Crystallization Behavior and Dielectric Properties of Li2O-Al2O3-SiO2 Photostructurable Glass Ceram. Int. (IF 3.057) Pub Date : 2018-08-13 Haolin Zhao, Jihua Zhang, Hongwei Chen, Tianpeng Liang, Meng Wei
Photostructurable Li2O-Al2O3-SiO2 glass is a promising material to fabricate complex three-dimensional structure with a high aspect ratio. However, its high dielectric loss at high frequencies has restrained its application in the field of integrated circuits packaging. In this research, La2O3, which has a large ionic radius, as well as strong polarization and bonding strength, was used to obstruct mobile ion migration to reduce the dielectric loss. The results indicated that moderate doping with La2O3 could effectively reduce the dielectric loss. When the dopant amount was 3%, the dielectric loss was successfully reduced to a minimum of 4×10-3 with a dielectric constant of 6.6 at 1 GHz, and this sample also possessed the optimal dielectric-temperature stability. Additionally, the effects of doping on the photosensitivity and crystallization behavior were also analysed. The results suggested that La2O3 doping did not affect the photosensitivity and selective crystallization characteristics. However, La2O3 restrained the precipitation of silicate from the [SiO4] tetrahedron, resulting in a decrease of nucleation rate and a delay of crystallization.
Reduced leakage current, enhanced energy storage and dielectric properties in (Ce,Mn)-codoped Ba0.6Sr0.4TiO3 thin film Ceram. Int. (IF 3.057) Pub Date : 2018-08-13 J. Qian, C.H. Yang, Y.J. Han, X.S. Sun, L.X. Chen
Ba0.6Sr0.4TiO3, Ce-doped Ba0.6Sr0.4TiO3, Mn-doped Ba0.6Sr0.4TiO3, (Ce,Mn) co-doped Ba0.6Sr0.4TiO3 (abbreviated as BST, BSTCe, BSTMn, BSTCeMn) thin films were deposited on LaNiO3(LNO)/Si substrates. The effects of ion doping on the microstructure and electrical properties of BST-based thin film have been researched and discussed. The X-ray diffraction pattern shows that each sample has pure perovskite phase structure with high (l00) peaks. The microstructure of each film is quite dense with uniform size. Compared with pure BST, improved insulating properties can be found in ion-doped BST thin films. For all the films, Ohmic conduction, space charge limited conduction and interface-limited Fowler-Nordheim tunneling should be the main conduction mechanisms within different electric field regions. For the case of BSTCeMn thin film, it possesses enhanced energy storage performance with a recoverable energy storage density (18.01 J/cm3) and a energy storage efficiency (75.1 %) under 2000 kV/cm. This can be closely related to the small remanent polarization value (Pr=1.89 μC/cm2), large maximum polarization value (Pmax=28.08 μC/cm2) as well as big maximum electric field (2000 kV/cm). Also, it exibits a large dielectric constant of 405 and a small dissipation factor of 0.075 at 500 kHz.
The role of high-valent (Mo and V) cations in defect spinel iron oxide nanomaterials: toward improving Li-ion storage Ceram. Int. (IF 3.057) Pub Date : 2018-08-13 Sameh I. Ahmed, Zein K. Heiba, N.Y. Mostafa, Abdallah A. Shaltout, Hend S. Aljoudy
Defect spinel Fe3-δO4 samples doped with high-valent Mo and V cations have been prepared by sol-gel auto-combustion rout with increasing concentrations of Mo and V, respectively. Energy Dispersive X-ray fluorescence (EDXRF) and Attenuated Total Reflection Fourier transform Infrared (ATR-FTIR) spectroscopies have verified the compositions of the samples and the oxidation states of the metal cations. Synchrotron Radiation X-ray Powder Diffraction (SR-XRPD) patterns were measured at MCX beamline of ELETTRA synchrotron. Structure and microstructure of the samples were studied by the Rietveld method. Increasing densities of vacancies were found to be generated by the high-valent Mo and V cations which were correlated to the lattice parameter, crystallite size and microstrain of each sample. The hysteresis loops were measured at room temperature using the Vibrating Sample Magnetometer (VSM) and good agreement was found between the Fe-cation distributions revealed from Rietveld adjustments and those predicted by the saturation magnetization (Ms) measurements. The High-Resolution Transmission Electron Microscopy (HRTEM) confirmed the proposed isotropic crystallite size model implemented in the Rietveld adjustments. Finally, the results presented herein show agreement with previous works on iron oxide materials used as intercalation cathode for Li-ion batteries and predict better performance for the current Mo- and V-doped defect spinel.
Luminescent properties of MgAl2O4 ceramics doped with rare earth ions fabricated by spark plasma sintering technique Ceram. Int. (IF 3.057) Pub Date : 2018-08-13 D. Valiev, O. Khasanov, E. Dvilis, S. Stepanov, E. Polisadova, V. Paygin
MgAl2O4 ceramics doped with rare earth ions (Eu2+ and Ce3+ ions) were fabricated by spark plasma sintering technique. A complex characterization of the crystalline and defect structure of the ceramic by XRD was carried out. Absorption, excitation, photo- and cathodoluminescence spectra were studied. The photoluminescence spectrum shifts to the blue region with a maximum at λem =475 nm for the MAS:0.1Ce ceramics. The nature of this luminescence can be caused by the radiative transitions in the cerium ion 5d – 4 f. The emission spectrum of MAS:0.1Eu has a “green” band emission in range of 400–700 nm centered around 500 nm, which can be ascribed to the allowed 4 f65d1→4f7 (5d – 4f) transition of Eu2+. In the millisecond time range, simultaneously with the emission of the complex host centers, the impurity luminescence bands of the chromium ion are recorded. It was shown that cathodoluminescence spectra in nanosecond time range can be decomposed into several emission bands at 2.72, 3.01, 3.37, 3.63–3.82 eV caused by F-type centers. It was demonstrated that the Eu2+ and Ce3+ ions lead to change the intensity ratio of the luminescence bands. The luminescence decay kinetics of synthesized spinel ceramics in nano- and millisecond time range were investigated in detail.
Gradient HfB2-SiC multilayer oxidation resistant coating for C/C composites Ceram. Int. (IF 3.057) Pub Date : 2018-08-13 Peipei Wang, Mingde Tong, Hanhui Wang, Hejun Li, Yujun Jia, Bo Li, Yulei Zhang, Zhigang Zhao
The gradient HfB2 modified SiC coating was prepared on the surface of SiC-coated C/C composites by in-situ synthesis. Anti-oxidation behaviors of the coated C/C samples at 1773, 1873 and 1973 K were investigated. The results show that the gradient HfB2 modified SiC coatings possess excellent oxidation resistance, which can protect C/C substrates from oxidation for 800, 305 and 100 h at 1773, 1873 and 1973 K, respectively. In addition, with the oxidation temperature increasing, the evaporation of the Hf-Si-O glass layer and the active oxidation of SiC were accelerated, which is the reason for the worst oxidation resistance of the sample at 1973 K among the three temperatures.
Some contents have been Reproduced by permission of The Royal Society of Chemistry.
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