"Fe2-xCrxO3氧化物之奈米微粒介電性質研究(x = 0, 0.3, 0.7,1, and 2)"

Abstract

本篇論文主要在討論關於Fe2-xCrxO3 ( x = 0, 0.3, 0.7, 1, and 2) 這一系列奈米顆粒的製備、特性及介電性質。這些奈米顆粒皆是以沉澱法製備。由 X-ray 粉末分析法可以得知，這系列樣本都擁有相同的菱形六面體結構，且皆為單相沒有雜質。平均的粒徑大小隨著燒結溫度上升而增加，大約落在30奈米至120奈米之間。而 SEM 的結果顯示隨著鍛燒的溫度不同，粒子的大小和形狀會有顯著的變化。這系列樣本皆以溫度和頻率作為變數來測量介電常數 e’(T) 、介電損耗 tanD、複數 modulus (M’, M”) 、 AC 電導率和磁化率。在室溫下除了 x = 2 的樣本以外，介電常數e’(T)皆隨著粒徑大小增加而上升，並且對應至介電損耗 tanD圖中的一個峰值。利用複數 modulus 的計算可辨別 grain 和 grain boundary 對整個介電系統的影響，並發現在室溫時 grain boundary 對整個系統的影響較 grain 顯著。 目前在此篇論文的發現可以使其他研究者對於反鐵磁 Fe2-xCrxO3 系統的介電性質有更深入的了解，甚至擴展至其他反鐵磁化合物及其應用。

The synthesis, characterization and dielectric properties of Corundum Fe2-xCrxO3 (x = 0, 0.3, 0.7, 1, and 2) nanoparticles were investigated. These nanoparticles were synthesized by co-precipitation method. The resulting X-ray diffraction patterns show that all these nanoparticles are single phase corundum structure. The average particle sizes were found to vary from ~ 30 nm to ~ 120 nm with increasing annealing temperature from 500 oC to 1000 oC. At room temperature, the real part of dielectric permittivity e'(T) increases with increasing particle size in all compositions except for x = 2. The corresponding loss tangent tanD(T) curves exhibits maxima. These peak positions shift to higher temperature as the measuring frequency increases, indicating thermally activated relaxation process. Complex modulus analysis was used to distinguish the grain and grain boundary contribution to these nanoparticles. The results suggest that the dominance of grain boundary resistance at room temperature in all compositions. So far, the discovery in this thesis may provide a better understanding of the dielectric properties of the antiferromagnetic Fe2-xCrxO3 system to other researchers. It might be even extended to other antiferromagnetc compounds and their applications.