不同鍶鈦比對鈦酸鍶之燒結行為和微結構以及介電性質的影響

Abstract

為了滿足通訊科技對更高的頻寬、更多資料傳輸量的要求，微波介電材料的發展顯得日益重要。鈦酸鍶為微波介電材料的一種，一直以來受到學術界許多的關注。在本研究中，利用固態反應法配製不同鍶鈦比的鈦酸鍶，鍶鈦比範圍為0.95到1.05。當研究不同鍶鈦比鈦酸鍶的燒結行為，根據燒結動力數據結果發現，鍶鈦比小於等於一的試片在低溫下收縮較慢，然而隨著溫度升高到1250℃之後，其收縮速率超越鍶鈦比大於一的試片且在1400℃燒結後擁有較高的緻密度。在微結構上兩者也有許多差異，在鍶鈦比大於一的試片觀察到等軸晶和咖啡豆形貌晶粒同時存在，且有異常晶粒成長現象；反之，鍶鈦比小於等於一試片則只觀察到等軸晶且鍶鈦比小於一的試片可看到二氧化鈦在晶界上。結果顯示不同鍶鈦比會大幅影響鈦酸鍶的燒結行為、微結構以及二次相的多寡而介電性質則容易受到上述因素所影響。在低頻量測下，鍶鈦比小於一試樣有較高的共振品質因子；然而在微波頻段下，各組成的共振品質因子沒有明顯的差異，另外鍶鈦比小於等於一的試樣的介電常數較高且介電常數隨著鍶鈦比的增加而下降。

Nowadays, in order to meet the request for higher speed and larger data transmission for telecommunication, the development of the microwave dielectric ceramics is crucial. SrTiO3 is a dielectric ceramic which has drown lots of attention for a long time. In the present study, the SrTiO3 powders with various Sr/Ti ratios were prepared using a solid state reaction. The Sr/Ti ratio varied from 0.95 to 1.05 with a step of 0.01. The sintering behavior of SrTiO3 as a function of Sr/Ti ratio was then investigated. Using TMA analysis, the Ti-rich and Sr/Ti=1.00 SrTiO3 specimens showed a lower densification rate at low temperature; however, their densification rate was higher than Sr-rich ones above 1250℃. Their density after sintering at 1400℃ was also higher. The morphology for the Sr-rich SrTiO3 showed the mixture of the equiaxed and coffee bean-like grains. On the other hand, the morphology for Ti-rich and Sr/Ti=1.00 SrTiO3 specimens exhibited equiaxed shape only. Some TiO2 second phase particles were located at the grain boundary for Ti-rich SrTiO3. Abnormal grain growth could be found in Sr-rich specimens. Some pores were trapped inside the abnormal grains. The Sr/Ti ratio strongly affected the shrinkage rate, relative density, microstructure, and the amount of second phases. As a consequence, the dielectric properties were influenced by these factors. At low frequency (1MHz), the Ti-rich SrTiO3 showed a higher quality factor. It may be related to their higher relative density and higher chemical defect concentration. Nevertheless, under microwave frequency, the quality factor of SrTiO3 specimens showed no dependence on Sr/Ti ratio. Moreover, the Ti-rich and Sr/Ti=1.00 specimens exhibited higher permittivity and the permittivity gradually decreased with increasing Sr/Ti ratio.