鑭系鋇釕雙鈣鈦礦氧化物之介電性質

Abstract

本論文研究鑭系元素之鋇釕雙鈣鈦礦Ba2LnRuO6 (Ln = La、Pr、Nd) 的介電性質研究，這系列的樣品製作是固態方法壓碇烘烤而成，於不同的鍛燒、和退火過程觀察其介電性質不同，SEM觀察其樣品表面構造，藉由X-ray粉末繞射法觀察其晶體結構，其結果皆為立方晶系，這系列晶格大小符合鑭系收縮的趨勢。以溫度和頻率為變數量測其介電常數和阻抗等電特性，ε’ (T)在低溫與溫度無關，隨著溫度升高開始射散，在ε’ (T)圖上的階梯對應到tan δ的峰值，表示在相變化時的能量損耗最大，當頻率增加峰值往高溫偏移。此外不同製程過程其結果也不同，樣品的烘烤過程若有退火，從Cole - Cole plot可明顯觀測到樣品的grain與grain boundary,若沒有退火步驟，則只看到grain。在導電率σ_T(ω)圖中可發現相變化，高溫時有兩段不同斜率，分別為grain和grain boundary所貢獻，當溫度下降到某一程度時，只有一條斜率表示只剩grain有貢獻，由於在低溫時沒有足夠大的熱活化能使grain boundary的電子躍遷。最後我們根據Arrhenius’s law計算各樣品的熱活化能，並且以Debye model和CPE model模擬樣品中的等校電阻，更進一步計算其電阻值與電容值。

The samples of Ba2LnRuO6 (Ln = La, Pr and Nd) were prepared by solid state method and the structure characterized by X-ray diffraction (XRD), Scanning electron microscopy (SEM), measureing the dielectric and impedance is to explore the properties of the system. The double perovskite of Ba2LnRuO6 have been confirmed with the cubic crystal structure. The dielectric properties were studied in the range of 20 Hz – 1 MHz, the constant ε' exhibited 10 ~ 103 from 10 K to 300 K. The steps of ε^' (T) correspond to the peaks of tanδ(T) exhibited relaxations, and it shifted to higher temperature as the frequency increases. In addition, the different calcination process made the result distinct, we could find the impedances came from grain and grain boundary obviously which the sample sintered with quench, or there is just one semi-circle in Cole - Cole plot that represents only grain contribution. Furthermore, we could find the phase transition that at high temperature there are grain and grain boundary, as the temperature drop only grain exist due to have not enough thermal energy to make grain boundary activated. We calculated the activated energy of the samples according the Arrhenius’s law, and simulated the equivalent circuit of impedances by CPE model and Debye model, further to calculated the values of capacitances and resistances in various temperatures.