Guo Jing, Zhou Di, Li Yong, Shao Tao, Qi Ze-Ming, Jin Biao-Bing, Wang Hong
Electronic Materials Research Laboratory, Key Laboratory of the Ministry of Education & International Center for Dielectric Research, Xi'an Jiaotong University, Xi'an, 710049, China.
Dalton Trans. 2014 Aug 21;43(31):11888-96. doi: 10.1039/c4dt00838c.
A novel series of microwave dielectric ceramics (Na0.5xBi0.5xCa1-x)MoO4 (0 ≤ x ≤ 0.6) was synthesized by the solid state reaction method. The crystal structures, microstructures, dielectric responses, and vibrational properties were investigated using X-ray diffraction, scanning electron microscopy, a microwave network analyzer, and terahertz, Raman and infrared spectroscopies. All the samples could be sintered well below 850 °C and a scheelite solid solution could be formed without any secondary phase. At x = 0.5 and x = 0.6, low-firing (750-775 °C) high performance microwave dielectric materials were obtained with permittivities of 19.1-21.9, Q × f values of 20 660-22 700 GHz, and near-zero temperature coefficients. The factors affecting microwave dielectric properties were discussed based on the vibrational data. As revealed by Raman spectroscopy, the disorder degree grows with x rising, which might increase the permittivities and decrease the Q × f values. The infrared spectra were analyzed using the classical harmonic oscillator model, and the complex dielectric responses gained from the fits were extrapolated down to the microwave and THz range. It is believed that the external vibration modes located at low frequencies dominate the main dielectric polarization contributions, especially the Na-O/Bi-O translational mode. This result indicates that the microwave dielectric properties of (Na0.5xBi0.5xCa1-x)MoO4 ceramics mainly depend on the behavior of AO8 polyhedra.
采用固态反应法合成了一系列新型微波介质陶瓷(Na0.5xBi0.5xCa1-x)MoO4(0≤x≤0.6)。利用X射线衍射、扫描电子显微镜、微波网络分析仪以及太赫兹、拉曼和红外光谱对其晶体结构、微观结构、介电响应和振动特性进行了研究。所有样品均可在850℃以下良好烧结，且能形成白钨矿固溶体，无任何第二相。在x = 0.5和x = 0.6时，获得了低温烧结(750 - 775℃)的高性能微波介质材料，其介电常数为19.1 - 21.9，品质因数与频率乘积值为20660 - 22700 GHz，温度系数接近零。基于振动数据讨论了影响微波介电性能的因素。拉曼光谱表明，无序度随x的增大而增加，这可能会提高介电常数并降低品质因数与频率乘积值。利用经典谐振子模型对红外光谱进行了分析，并将拟合得到的复介电响应外推至微波和太赫兹频段。据信，低频处的外部振动模式主导了主要的介电极化贡献，尤其是Na-O/Bi-O平移模式。该结果表明，(Na0.5xBi0.5xCa1-x)MoO4陶瓷的微波介电性能主要取决于AO8多面体的行为。
