R2BaNiO5氧化物巨介電性質之研究 (R = Nd, Sm, Eu, Gd, Dy, Ho, Er, and Y)

Abstract

R2BaNiO5 (R = Nd, Sm, Eu, Gd, Dy, Ho, Er, and Y) 這一系列的化合物是用固態的方法於不同的鍛燒溫度(TA) 來作和成的. 我們量測它們的介電性質並觀察它們的晶體結構. 藉由使用 X-ray 粉末分析法, 我們發現此系列化合物都同擁有相同的單相斜方晶體結構. 而 SEM 告訴我們隨著鍛燒的溫度不同, particle 的大小和形狀會有顯著的變化. 我們以溫度和頻率作變數來量測介電常數(ε’), 介電損失(tan δ), 複數modulus (M’, M’’) 和 AC電導率這些化合物特性的值. 在室溫下, 每個樣品都可量到巨介電常數而且發現這和晶體的結構有強關聯性. 所有的樣品在ε’ (T) 的圖中, 介電常數皆呈階梯式增加, 並且皆對應一個峰值在 tan δ 圖中. 我們利用複數modulus 的計算來辨別出 grain 和 grain boundary 對整個介電系統的影響, 並發現在高溫時 grain boundary 對整個系統較 grain 佔有更大的影響. 目前在此篇論文的發現可能會對 R2BaNiO5 的其他介電性質提供更大的潛力來研究, 甚至因而發現其它新的擁有巨介電常數的化合物.

R2BaNiO5 (R = Nd, Sm, Eu, Gd, Dy, Ho, Er, and Y) ceramic samples were prepared by solid state reaction method at different annealing temperatures (TA), and the dielectric responses were evaluated together with the micro-structures. Powder X-ray analysis reveals the formation of a single-phase orthorhombic structure with Immm space group in all the samples. Micro-structural analysis, SEM, shows a significant change in the particle size and the morphology with TA. The dielectric constant (ε’), dielectric loss (tan δ), complex modulus (M’, M’’) and AC conductivity (σAC) were studied as a function of frequency and temperature for all the samples. The giant dielectric constant was obtained in all samples at room temperature, and strong processing and microstructure dependence of dielectric characteristics of the present ceramics was determined. All samples show a step type increase in ε’ (T) and corresponding peaks in tan δ curves. Complex modulus analysis was used to distinguish the grain and grain boundary contribution to the system, suggesting the dominance of grain boundary resistance at high temperature in all samples. The present findings would offer the great potential for enhancing dielectric constant in R2BaNiO5 ceramics by optimizing the microstructure and supplies an approach in searching for new giant dielectric constant material.