Recrystallization of fine-crystalline barium titanate in low-density water medium
Graphical abstract
Introduction
Nowadays metal-oxide-based materials count a great deal in different branches of industry such as production of energy storage and memory devices, coatings, catalysis, etc. [[1], [2], [3]]. Metal oxides applications are closely related to possibility of tailoring their structural and morphological properties. Methods of synthesizing metal oxides appear of interest if they allow control of phase content, particle shape and size. Some of the state-of-the-art approaches involve the use of water vapor below the critical point and/or supercritical water as a medium for treatment of oxide or organometal precursors [[4], [5], [6], [7], [8], [9], [10], [11], [12], [13]]. The process could be realized either in a flow or in a batch reactor and yields pure crystalline product of size ranges from nano to microns. Depending on the nature of reagents, the reaction could be routed by hydrothermal-like or sol-gel-like mechanisms [4]. Sub- and supercritical hydrothermal synthesis seems to be more attractive from the economic and ecological viewpoints: the process requires less expensive reagents and auxiliary compounds and could be characterized by higher atomic efficiency. In this case the reaction of starting salts or hydroxides might proceed by a combination of two mechanisms: dissolution-precipitation and in situ transformation [[14], [15], [16], [17], [18], [19], [20]]. The former involves nucleation of the product from a solution, while the latest implies formation of product layer at the surface of initial reagent particles. Which of two mechanisms prevails, depends on the state of reaction medium and on the properties of reagents such as phase modification, crystallinity, particle size, etc. Activation of the reagents occurs via hydration and hydroxylation followed by their dissolution or remaining of the compound in a solid state. In sub- and supercritical conditions water molecules and hydroxyl groups play one of the key roles in reagents’ transformation to the product [21,22]. As it was demonstrated for the synthesis of different complex oxides (BaTiO3, PbTiO3, Pb(Zr,Ti)O3, SrTiO3, Zn2SnO4, etc.), when dissolution-precipitation mechanism is realized in a liquid medium or high-density supercritical water, the reaction occurs between hydrated and hydroxylated species in a solution [21,23,24]. On the other hand, simple metal oxides structure formation is known to proceed owing to solid-phase mobility in precursors which appears at elevated temperature in the medium of subcritical vapor or low-density supercritical water (thermovaporous treatment, TVT) [[25], [26], [27]]. For instance, well-crystallized α-Al2O3 was obtained from boehmite AlOOH as a precursor [28]. Solid-phase mobility promoted by TVT of simple oxides mixture provides formation of complex oxide structures such as Y3Al5O12, MgAl2O4, LaAlO3, ZnAl2O4, BaFe12O19, LiNbO3, BaTiO3 [26,[29], [30], [31]]. TVT is accompanied by dissociative adsorption of water molecules on the surface of simple oxide particles and gradual saturation of their volume with hydroxyl groups [26,32]. Finally, the processes of hydration and dehydration of metal oxide matrix achieve quasi-equilibrium. Numerous acts of formation and breaking of new Me-O-Me bonds are accompanied by local rearrangements, which determine the solid-phase mobility and result in ordering of the crystal structure. Impact of water on the structural transformation of solid oxides results in significant decrease in the reaction temperature compared to the processes in anhydrous media. For example, α-Al2O3 is formed from transition modifications of aluminum oxides in air on heating above 1100 °C [[33], [34], [35]]. In TVT conditions, formation of fine-crystalline α-Al2O3 occurs at 400 °C [25,26]. Barium titanate could be obtained by TVT of barium and titanium oxides mixture at temperature as low as 110 °C [36] while in anhydrous medium heating up to 850−1400 °C is required for this reaction [37,38].
The oxide structures formed in sub- and supercritical water were revealed to contain residual hydroxyl groups trapped in oxygen vacancies as well as chemically or physically adsorbed at the surface of particles [22,26,[39], [40], [41]]. The residual structural hydroxyls were shown to favor recrystallization of oxides, for example, α-Al2O3 during TVT [42]. When discussing the recrystallization phenomenon, we imply the process of crystal growth in a single-phase powder which occurs owing to mass transfer from smaller to larger crystals and is accompanied by defect elimination and structure perfection. Practically, recrystallization is of high importance since it allows improvement of structure, morphology and functional properties of metal oxides [[43], [44], [45], [46]]. Current paper is devoted to study of recrystallization in fine-crystalline BaTiO3 in the medium of subcritical vapor and supercritical water.
Fine BaTiO3 powder is widely used as a raw material for capacitor ceramics, piezoceramic voltage transducers, PTC resistors, etc. [[47], [48], [49]]. Production lines require BaTiO3 powders of different fractional composition depending on functionality of final material. Additional processing of the synthesized BaTiO3 powder in the reaction medium of vapor or supercritical water studied in the present work would contribute to the improvement of its quality as a material for electronics industry.
Section snippets
Experimental
Standard commercially available reagents were utilized in the synthesis of BaTiO3: Ba(OH)2·H2O (>99 % purity) with particle size of less than 50 μm and TiO2 (>98 % purity) in anatase modification with average particle size of 0.122 ± 0.001 μm. TVT of the mixed reagents was carried out in laboratory autoclaves of 17 ml internal volume following the technique described elsewhere [31,50]. The mixture of starting oxides with the molar ratio BaO/TiO2 = 1.25 was prepared by their joint fivefold
Results and discussion
Fig. 1 shows SEM image, XRD pattern, and crystal size distribution for each of the synthesized BaTiO3 samples. The synthesis was carried out in the same conditions (the first stage of TVT). Conditions of the second stage of TVT differed among the samples. Single phase composition of barium titanate was revealed for all the samples s1-s4. The shape of crystals formed at 200 °C appeared nearly spherical (Fig. 1, sample 1). Prolonged treatment at 200 °C resulted in the increase of CSR size of BaTiO
Conclusion
Crystalline barium titanate synthesized from titanium dioxide and barium hydroxide monohydrate in a medium of water vapor (200 °C, 1.55 MPa) underwent recrystallization during subsequent prolonged treatment in vapor or supercritical water at 200−400 °C, 1.55–26.3 MPa. Formation of BaTiO3 powder proceeded in two stages: first, rapid formation of crystalline barium titanate, and second, slow mass redistribution between the crystals accompanied by ordering of their structure. While the average
Declaration of competing interest
The authors declare no conflict of interest.
Acknowledgements
The work was carried out with the financial support of The Ministry of Education and Science of the Russian Federation within the framework of the State Task “The Development of a Perspective Method for Obtaining of Ultra Dispersive Barium Titanate (BaTiO3) as a Main Component in the Production of Ceramic Capacitors” No. 0699-2017-0005 from May, 31 2017 and with the use of equipment of the Centre of Collective Usage “High Technology in Engineering” of Moscow Polytech (Number for publications:
References (64)
- et al.
Metal oxide nanostructures in sensing
- et al.
WWMOD? What would metal oxides do? redefining their applicability in today’s energy technologies
Polyhedron
(2019) - et al.
Supercritical fluid technology: a reliable process for high quality BaTiO3 based nanomaterials
Adv. Powder Technol.
(2014) - et al.
Continuous BaTi1−yZryO3 (0≤y≤1) nanocrystals synthesis in supercritical fluids for nanostructured lead-free ferroelectric ceramics
Mater. Des.
(2015) - et al.
Coupling in situ synchrotron radiation with ex situ spectroscopy characterizations to study the formation of Ba1−xSrxTiO3 nanoparticles in supercritical fluids
J. Supercrit. Fluids
(2014) - et al.
Effect of titanium dioxide solubility on the formation of BaTiO3 nanoparticles in supercritical water
Fluid Phase Equilib.
(2007) - et al.
Rapid synthesis of BaTiO3 nanoparticles in supercritical water by continuous hydrothermal flow reaction system
J. Supercrit. Fluids
(2008) - et al.
Hydrothermal synthesis of BaTiO3 nanoparticles using a supercritical continuous flow reaction system
J. Cryst. Growth
(2010) - et al.
Effect of water density on polymorph of BaTiO3 nanoparticles synthesized under sub and supercritical water conditions
Mater. Lett.
(2005) - et al.
Evidence of a dissolution-precipitation mechanism in hydrothermal synthesis of barium titanate powders
J. Eur. Ceram. Soc.
(1999)
Formation mechanisms and morphological changes during the hydrothermal synthesis of BaTiO3 particles from a chemically modified, amorphous titanium (hydrous) oxide precursor
J. Eur. Ceram. Soc.
Crystalline barium titanate synthesized in sub- and supercritical water
J. Supercrit. Fluids
Synthesis and investigation of crystalline modifications of silicon dioxide
React. Solids.
The role of water fluid in the formation of fine-crystalline oxide structure
J. Supercrit. Fluids
Synthesis of Eu-doped gahnite in water and water-ammoniac fluids
J. Supercrit. Fluids
Content and diffusion of water and gases in MgAl2O4 spinel crystals synthesized to produce ceramics
J. Eur. Ceram. Soc.
Synthesis of monodispersed barium titanate nanocrytals - Hydrothermal recrystallization of BaTiO3 nanospheres
J. Cryst. Growth
Crystallization temperature effect on tungsten oxide thin films prepared by sol-gel method for ultraviolet-visible photodetectors
Sensors Mater.
Barium titanate based ceramic materials for dielectric use
Int. J. High Technol. Ceram.
Low-temperature synthesis of BaTiO3 nanopowders
Ceram. Int.
Synthesis and characterization of BaTiO3 nanoparticles in oxygen atmosphere
J. Alloys. Compd.
Properties of barium titanate ceramics based on powder synthesized in supercritical water
Ceram. Int.
Synthesis, Design, and Morphology of Metal Oxide Nanostructures, in: Metal Oxide Nanostructures
Local distortions in nanostructured ferroelectric ceramics through strain tuning
Adv. Electron. Mater.
Hydrothermal synthesis of metal oxide nanoparticles at supercritical conditions
J. Nanopart. Res.
Preparation of fine-grained corundum powders with given properties: crystal size and habit control
Theor. Found. Chem. Eng.
Subcritical solvothermal synthesis of condensed inorganic materials
Chem. Soc. Rev.
Kinetics of barium titanate synthesis
J. Am. Ceram. Soc.
Nucleation and formation mechanisms of hydrothermally derived barium titanate
ACS Symp. Ser. Vol. 681.
Kinetics and mechanisms of hydrothermal synthesis of barium titanate
J. Am. Ceram. Soc.
Real time observation of the hydrothermal crystallization of barium titanate using in situ neutron powder diffraction
J. Am. Chem. Soc.
Hydrothermal synthesis of ferroelectric perovskites from chemically modified titanium isopropoxide and acetate salts
J. Mater. Res.
Cited by (8)
Recrystallization of nanosized boehmite in an aqueous medium
2023, Powder TechnologyCitation Excerpt :The authors [9] believe that recrystallization is associated with the diffusion spreading of the substance of crystals with a mobile structure over the surface of crystals with reduced structural mobility until the counter mass flows are equal. A similar transformation pattern was found when studying the recrystallization of the synthesized barium titanate [10]. Barium titanate was synthesized by treating a mixture of powders of barium hydroxide monohydrate and titanium dioxide in steam at 200 °C.
Volatile impurities in the structure of Y<inf>3</inf>Al<inf>5</inf>O<inf>12</inf> garnet synthesized in water fluid
2021, Journal of Supercritical FluidsCitation Excerpt :To produce doped and undoped garnet, the sol-gel method, followed by heating at temperatures above 1000 °C [30–34], the method of coprecipitation from salt solutions [35,36] and others [37–45] are used. Recently, the method of synthesis of powder functional materials in the medium of sub- and supercritical water fluid has become widespread due to efficiency, technological availability, and environmental safety [46–55]. It was used to produce fine-crystalline simple oxides SiO2, Al2O3 but also complex oxides MgAl2O4, ZnAl2O4, LaAlO3, BaTiO3 and others.
Anomalous conductivity behavior induced by in situ metastable amorphous phase in BaTiO<inf>3</inf>/Ni<inf>0.5</inf>Zn<inf>0.5</inf>Fe<inf>2</inf>O<inf>4</inf> ceramic composite
2020, Ceramics InternationalCitation Excerpt :For the a-BTO/NZFO composite, the transition of Edc near 513 K may be probably associated with a transition from disordered-vacancy phase to ordered-vacancy phase in the a-BTO phase at elevated temperature. With ΔHt<0 when the temperature increases from Region II to Region I, one can speculate that an exothermic process that is responsible for the decrement in Edc might occur above the critical temperature (T*≈513 K), which probably associates with the initial crystallization of the a-BTO phase as c-BTO can come into being at a relatively lower temperature in a hydrothermal process (473–673 K) or in a TiO2-seeded hydrothermal process (423–483 K) [46,47]. Owing to such ΔHt<0 process, the mobility of oxygen vacancies may get undermined in the metastable a-BTO phase, leading to decreased electrical conductivity above 513 K.
Synthesis of Mixed La–Al Oxides by Treatment in a Water Fluid Medium and Their Catalytic Properties in Methane Oxidation
2023, Russian Journal of Physical Chemistry BEffect of Mechanical Pressure on the Recrystallization of Zinc Oxide in a Water Fluid Medium under Cold Sintering
2021, Russian Journal of Physical Chemistry B