鎢酸鋇-鈮酸鋇複合陶瓷之燒結行為與微波介電性質

Abstract

本研究以20, 40, 60, 80 wt% 鈮酸鋇加入鎢酸鋇粉末中，以乾壓成型生胚，並在1200 度至1400 度燒結製備成複合陶瓷，觀察其燒結行為、微結構、結晶相與微波介電性質。實驗結果顯示不同成分含量的試片會顯著影響其微結構與微波介電性質，其中介電常數隨著鈮酸鋇添加量而上升。本研究亦發現添加80 wt%鈮酸鋇的微結構中，由於鈮酸鋇添加量夠多足以包覆鎢酸鋇晶粒，而使鎢酸鋇晶粒內部的微裂縫消失，因此進一步使該成分的試片有最高的品質因子(37000 GHz)。由於鎢酸鋇與鈮酸鋇的共振頻率溫度係數(tf)分別為-60 ppm/°C 與78 ppm/°C，在此複合陶瓷系統中兩相的tf 會互相抵銷趨近於零，例如其中含40 wt%鈮酸鋇的複合材料擁有最接近零之tf(4.3 ppm/°C)。

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.