Sintering Behavior and Microwave Dielectric Propertiesof BaWO4-Ba5Nb4O15 Composite Ceramics

• Main Authors: Chiao-Yi Tsai, 蔡蕎伊
• Other Authors: 段維新
• Format: Others
• Language: en_US
• Published: 2017
• Online Access: http://ndltd.ncl.edu.tw/handle/fyn7kc

碩士 === 國立臺灣大學 === 材料科學與工程學研究所 === 105 === In the present study, the BaWO4 and Ba5Nb4O15 are sintered together to form composite. By adding 20, 40, 60, 80 wt% Ba5Nb4O15 into BaWO4, extra attention has been paid to the sintering behavior, microstructure, phase identification and microwave dielectric properties of composites. The preparation of pure BaWO4 and Ba5Nb4O15 has been done by sintering at 1100 °C and 1250 °C, respectively. As the sintering temperature was higher than 1100 °C, the cracks are spontaneously formed at the grain boundaries between BaWO4 grains; it is may due to the anisotropic thermal shrinkage and the vaporization of WO3. The relative density of Ba5Nb4O15 is also decreased after sintering above 1300 °C; it is likely due to the abnormal grain growth at elevated temperature. The composites with 20, 40 and 60 wt% Ba5Nb4O15 can be densified after sintering at 1350 °C. The relative density can reach above 92%~95%. The relative density of the composites with 80 wt% Ba5Nb4O15 reaches 90% after sintering at 1250 °C. The permittivity for the composites of 20, 40, 60 and 80 wt% Ba5Nb4O15 increases from 14 to 30 along with weight percent of Ba5Nb4O15. The permittivity of the composites follows the logarithm mixture law. The addition of 80 wt% Ba5Nb4O15 into BaWO4 exhibits the highest quality factor of 37000 GHz. To compare with other compositions, the microstructure without microcracks is a key factor to affect the quality factors. The BaWO4 and Ba5Nb4O15 show opposite tf values offsetting each other in the system. The tf value thus increases with the content of Ba5Nb4O15 as well. The tf value for the composites containing 40 wt% Ba5Nb4O15 is only 4.3 ppm/°C.