"Ba2ReMoO6化合物之介電性質研究 (Re = Sm, Eu, Nd, Gd, Dy, Y)"

Abstract

此篇論文主要探討Ba2ReMo6化合物的介電性質，這一系列的化合物都是採用固態反應法合成。藉由X-RAY分析可以知道此類化合物結構均為立方晶系，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’’)來分析這些化合物的特性。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。在Ba2SmMoO6樣品，我們發現在tan δ的兩個峰值，其中之一個峰值的溫度(~ 160 K)對應到此樣品磁相變附近的溫度，可以證實此唯一多鐵材料。此一多鐵材料可以提供後人對多鐵材料性質去做更深入探討及研究

The synthesis, characterization and dielectric properties of polycrystalline Ba2ReMoO6 (Re = lanthanide or Y ion) compounds were investigated in this thesis. Powder X-ray diffraction patterns reveal that all the samples are single phase cubic structure with Fm3m space group. The refined lattice parameters and volume obey the Lanthanide contraction rule. The dielectric properties of these compounds were studied in the frequency range from 20 Hz to 1 MHz between 20 K and 320 K. The Ba2SmMoO6 sample exhibits a high dielectric permittivity (ε' ~ 104) at room temperature with frequency dispersion. In addition, ε'(T) also show a two steps like increases at low temperature. The corresponding tanδ(T) curves exhibit two relaxations at T < 60 K and ~ 160 K. The peak temperature TP of tanδ(T) shifts to a higher temperature as the frequency increases in both relaxations. The overall behavior of high temperature ε' and tanδ is similar to that observed in giant dielectric constant materials. The dielectric properties of Re = Nd, Eu, and Y are also exhibits two relaxations. Whereas Re = Gd and Dy show only one dielectric relaxation. The observed giant dielectric response was explained in terms of internal (grain boundary) barrier layer capacitance (IBLC) [6] effect and relaxation at ~ 160 K is related to the development of long-range antiferromagnetic order.