新型li基微波介电陶瓷的制备 结构及性能分析-preparation structure and performance analysis of new li - based microwave dielectric ceramics.docx

The content of the thesis is based on Li-inserting A3B8O21 hexagonal perovskite Ba3Nb4Ti4O21 ceramic and A(B1/2W1/2)O3 composite perovskite ceramics. A series ofmicrowave dielectric ceramics Ba3LixNb4-xTi4+xO21 (0≤x≤1)、LiBa3Nb3-xSbxTi5O21 (0≤x≤3)、LiBa3Ta3-xSbxTi5O21 (0≤x≤3) 、 Ba(Li2/5W3/5)O3 were prepared. Then crystal structure, micostructure and microwave dielectric properties of these compounds were investigated.Ba3Ti4Nb4O21 ceramics was synthesized by a standard solid-state techniquea, its high-temperature dielectric property and relaxation was investigated. The microwave dielectric properties are related to the oxygen vacancies inside the ceramic. Meanwhile, combining with the structure of A3B8O21 hexagonal perovskite Ba3Nb4Ti4O21 ceramic, we prepared Ba3LixNb4-xTi4+xO21 (0≤x≤1) ceramics through the conventional solid-state route. Single phase and dense ceramic was obtained in range of 0≤x≤1. Compared with Ba3Ti4Nb4O21(x=0) ceramic, the LiBa3Nb3Ti5O21(x=1)ceramic has good microwave dielectric properties with high dielectric constant (εr~78), quality factor (Q×f~9,800GHz), temperaturecoefficient of resonance frequency (τf~205ppm/?C) and the sintering temperature decreasedfrom 1320?C to 1100?C. For adjusting the temperature coefficient of resonance frequency of LiBa3Nb3Ti5O21 ceramic, LiBa3Nb3-xSbxTi5O21 (0≤x≤3) and LiBa3Ta3-xSbxTi5O21 (0≤x≤3) have been prepared through solid-state reaction method.Single-phase polycrystalline microwave dielectric ceramics LiBa3Nb3-xSbxTi5O21 (0≤x≤3) were prepared by the solid-state reaction method . The ceramics were well sintered at the temperatures ranging from 1100?C to 1220?C for 4h. The substitution of Sb for Nb effectively improved the quality factor and modified τf. With the increasing Sb content, the dielectric constant (εr) decreased from 78 to 27, the Q×f value enhanced significantly from 9,800 to 29,400GHz, and τf improving from 205ppm/?C to -25ppm/?C. A near zero τf value could be obtained when x=2.1.Singl