褐钇铌矿型微波介质陶瓷相变及其性能调控

本项目以晶体化学原理为依据，以褐钇铌矿LnNbO4（Ln=La、Nd、Sm等）为基础结构式，通过A位、B位、A/B位联合取代构建固溶体陶瓷及复合陶瓷，有效调节褐钇铌矿铁弹相变温度。拟通过Rietveld方法进行结构精修获取晶胞参数信息；利用Shannon加和理论及C–M关系研究离子极化率与宏观介电常数的关系；预期构建褐钇铌矿结构容忍因子，研究相变规律、极化机理及结构/性能关系；利用复杂晶体理论计算化学键强度、晶格能和热膨胀温度系数等参数；通过点群理论计算出红外及Raman响应模式，利用红外反射光谱及THz谱与复介电常数ε*之间的关系，将振动模式与其对介电性能的贡献联系起来，从而深入研究晶格结构、极化贡献及宏观介电性能的关系。该项目的实施预期进一步推动褐钇铌矿微波介质陶瓷结构与性能关系基础理论研究的发展，为开发面向5G介质滤波器用新型高品质因数的K20温度稳定型微波介质材料提供理论依据。

Based on the crystal chemical theory, the present proposal is focused on the design and preparation of novel series of fergusonite-type LnNbO4 (Ln=La, Nd, Sm, etc.) microwave dielectric materials and composites in forms of solid solution and composite by occupying the eight-coordinated A site using Bi3+, In3+, etc. and the four-coordinated B site V5+, Ta5+, Sb5+ in forms of single or complex substitution with tunable ferroelastic phase transition temperatures. Rietveld method will be employed to perform the crystal structure refinement; Shannon’s additive rule and C-M relation are used to study the relation between microscopic polarization and macroscopic permittivity; the tolerant factor of fergusonite will be defined to study the relation between phase transition, polarization mechanism, crystal structure and dielectric properties; bond strength, lattice energy and thermal expansion coefficient will be calculated from the theory of chemical bond; far-infrared and THz spectra will be fitted to study the intrinsic dielectric properties and vibration modes will be assigned to study its individual contribution to the polarization at microwave region. Generally the relation between composition, structure, phase transition (monoclinic fergusonite to scheelite structure), and microwave dielectric properties of LnNbO4 (Ln=La, Nd, Sm, etc.)-based fergusonite structured dielectrics with A-site substitution, B-site substitution and A/B site complex substitution modifications will be studied in detail. All the results will contribute to better understand the structure-property-relation of LnNbO4 (Ln=La, Nd, Sm, etc.)-based fergusonite structured dielectrics, and the exploration for 5G technology microwave dielectrics with K20 microwave dielectric permittivities, high quality factor (Qf), and near-zero temperature coefficient of resonant frequency.