Vibrational spectroscopy and microwave dielectric properties of two novel Ca3Ln2W2O12 (Ln = La, Sm) tungstate ceramics
Graphical abstract
Introduction
Over the past decades, in pace with the booming industry of microwave telecommunications, microwave dielectric ceramics have become indispensable components of various microwave devices due to their compactness, light weight, thermal stability, low cost and excellent performance [1]. From the device design perspective, dielectrics with suitable values of the dielectric constant (εr) are required for balancing device miniaturization and short signal delay time. A high Qf value (Q = 1/tanδ and f denotes the resonant frequency) can reduce the energy loss during signal propagation and create satisfactory frequency selectivity, which is of vital importance to minimizing the signal attenuation. In addition, a low temperature coefficient of resonant frequency (τf) is required for ensuring frequency stability. Last, for massive industrial production, the cost effectiveness is another important factor as the typical ultra-low-loss candidates, such as Ba-based complex perovskites, typically contain noble raw materials, such as tantalates or niobates [2,3]. The identification of a single material that satisfies all these requirements is a formidable task, and optimally balancing these properties is a major challenge in the microwave dielectric ceramics industry.
Tungstates have been regarded as important candidates for dielectric materials due to their low cost, facile synthesis, satisfactory chemical stability, and excellent dielectric properties. Among tungstates, AWO4 (A = Ca, Sr, Ba, Zn, Co, or Ni) compounds with monoclinic wolframite or tetragonal scheelite structures are well known [[4], [5], [6], [7]]. Pullar et al. reported that AWO4 ceramics that are sintered at 1200 °C typically exhibit low dielectric constant values of approximately 12 and Qf values in the range of 24,900–62,800 GHz [4]. In 2011, Li2WO4 ceramics with an ultra-low sintering temperature of approximately 650 °C were reported by Zhou et al., and their satisfactory microwave dielectric properties (εr ∼ 5.5, Qf ∼ 62,000 GHz, and τf =–146 ppm/°C) indicated high potential in ultra-low-temperature cofired ceramic (ULTCC) technologies [8]. More recently, various types of tungstates such as Li4WO5, LiAlW2O8, and Li2Mg2(WO4)3 were proposed, and their potential applications in microwave dielectric ceramics were systematically investigated [[9], [10], [11]]. Ca3Ln2W2O12 (Ln = La and Sm) powders are widely applied as promising host materials for inorganic phosphors due to their outstanding structural tunability and luminescent properties [[12], [13], [14]]. However, to the best of our knowledge, minimal investigation has been conducted on the potential applications of Ca3Ln2W2O12 ceramics or on their microwave dielectric properties. Therefore, the exploration of the structural parameters and microwave dielectric properties of Ca3Ln2W2O12 ceramics could be important, and may trigger a new breakthrough in the development of novel tungstate-based microwave dielectric ceramics that realize high performances.
In this study, the crystal structures and Raman spectra of Ca3Ln2W2O12 ceramics are systematically investigated, together with their effects on the microwave dielectric properties. Moreover, IR spectra are extrapolated to the microwave frequency region to further identify the intrinsic dielectric properties.
Section snippets
Experimental procedure
Ca3Ln2W2O12 ceramics were prepared via high temperature solid-state reactions of CaCO3 (99.99%), La2O3 (99.99%), Sm2O3 (99.99%) and WO3 (99.99%) raw powders. Prior to weighing, La2O3 and Sm2O3 were preheated at 900 °C for 2 h to remove the moisture. The stoichiometric powder was ball-milled with zirconia media at a speed of 180 r/min for 6 h. After that, the obtained mixtures were calcined at 1100 °C for 3 h and pressed into cylindrical pellets of 12 mm in diameter and 5 mm in height. Finally,
Results and discussion
The XRD patterns of Ca3Ln2W2O12 ceramics that were sintered at 1300 °C are presented in Fig. 1(a). Both patterns exhibit similar diffraction features, and all the diffraction peaks can be well indexed according to the standard PDF card of Ca3La2W2O12 (JCPDS #49-0965). Hence, monophasic Ca3Ln2W2O12 ceramics have been successfully obtained in this study. Based on the cell refinements, the cell parameters of Ca3Ln2W2O12 ceramics are calculated as follows: a = b =9.76375 Å, c =55.54702 Å, γ = 120°
Conclusions
Two novel tungstate ceramics with a nominal composition of Ca3Ln2W2O12 (Ln = La, Sm) have been prepared via standard solid-state reaction methods. The XRD results demonstrate the formation of monophasic Ca3Ln2W2O12 ceramics with a space group of R m. Dense microstructures with a hexangular-shape-like grain morphology are obtained when sintered at 1375 °C, where the optimal microwave dielectric properties (εr = 18.7, Qf = 50,500 GHz, and τf =–90 ppm/°C) are also realized in Ca3La2W2O12
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
Financial support from the National Natural Science Foundation of China under grants numberS 51802062 and 51672063 is greatly appreciated.
References (34)
Far-infrared reflection and microwave properties of Ba[(Mg1-xZnx)1/3Ta2/3]O3 ceramics
J. Eur. Ceram. Soc.
(2004)- et al.
Alford, MgWO4, ZnWO4, NiWO4 and CoWO4 microwave dielectric ceramics
J. Eur. Ceram. Soc.
(2007) - et al.
Microwave dielectric properties of AWO4 (A = Ca, Ba, Sr) ceramics synthesized via high energy ball milling method
J. Alloy Compd.
(2013) - et al.
Structural, optical and microwave dielectric properties of Sr1−xCaxWO4 ceramics prepared by the solid state reaction route
Ceram. Int.
(2013) - et al.
Microwave dielectric properties of (1−x)ZnMoO4–xTiO2 composite ceramics
J. Alloy Compd.
(2011) - et al.
4LiWO5: A temperature stable low-firing microwave dielectric ceramic with rock salt structure
J. Eur. Ceram. Soc.
(2016) - et al.
LiAlW2O8: A novel temperature stable low-firing microwave dielectric ceramic
Mater. Lett.
(2016) - et al.
Synthesis and microwave dielectric properties of Li2Mg2(WO4)3 ceramics
Mater. Lett.
(2015) - et al.
Sensibilisierte IR-Emission der Dreiwertigen Seltenen Erden in Ca3La2W2O12
J. Solid State Chem.
(1985) - et al.
Lumineszenz von Ca3La2W2O12: Mn und Ca3La2Te2O12: Mn
Mater. Chem. Phys.
(1985)
Enhancing the energy transfer from Mn4+ to Yb3+ via a Nd3+ bridge role in Ca3La2W2O12: Mn4+,Nd3+,Yb3+ phosphors for spectral conversion of c-Si solar cells
Dyes and Pigments
A new lithium hydrogen tellurate–LiH5TeO6
J. Solid State Chem.
Structural study of tungstate fluorophosphate glasses by Raman and X-ray absorption spectroscopy
J. Solid State Chem.
Structural evolution and microwave dielectric properties in Sr2(Ti1-xSnx)O4 ceramics
J. Eur. Ceram. Soc.
Microwave dielectric properties of temperature stable (1-x)SrLaAlO4-xTiO2 composite ceramics
Ceram. Int.
Crystal structure, infrared reflectivity spectra and microwave dielectric properties of CaAl2O4 ceramics with low permittivity
J. Alloy Compd.
Sintering behavior, phase evolutions and microwave dielectric properties of LaGaO3-SrTiO3 ceramics modified by CeO2 additives
Ceram. Int.
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