鈦酸鋇正溫度係數陶瓷電性研究

Abstract

本論文研究添加１莫耳百分率的氧化鎂、0.05莫耳百分率的二氧化錳及各 種不同濃度的氧化銻和氧化釔的鈦酸鋇陶瓷體。利用速率控制的燒結方法 比傳統方法可得到較均勻晶粒。鈦酸鋇陶瓷體的居里溫度可藉添加氧化銻 或氧化釔來改變。在鈦酸鋇陶瓷體中，鎂離子當作受體，而銻離子為施體 ，由於鎂離子的補償，使鈦酸鋇的半導性範圍移至較高的銻離子濃度。在 居里溫度和最大電阻率溫度的範圍內，介電係數和溫度乘積的倒數成線性 關係；能障高度可由圖中的斜率求出，本研究中發現能障高度隨銻離子濃 度遞增。由介電常數的倒數和溫度的關係圖中，發現介電係數只在一個小 溫度範圍內遵守居里偉斯定律( Curie-Weiss law ) ，此現象是由於受體 態位密度在高溫時逐漸減小的緣故。 Nonstoichiometric BaTiO3 ceramics with 1 mole% MgO, 0.05 mol % MnO2 and various amount of Sb2O3 and Y2O3 dopants are investi- gated. Specimens fired with a rate- controlled sintering profile exhibit a rather fine and uniform microstructure as compared to those processed by conventional sintering techniques. Curie tem- perature of BaTiO3-based ceramics is shifted with the addition of Sb2O3 and/or Y2O3. Magnesium ions acts as acceptors in the BaTiO3 lattice, while antimony, hence the doped-BaTiO3 semicon- ductive region is shifted to higher contents. Arrhenius plots of resistivity versus 1/εmT were found to give straight lines for Tc<T<Tmax. The height of potential ba- rriers at different temperatures, as calculated from the slopes of these plots, were found to increase with increasing Sb content. Plots of 1/εm vrsus temperature were found to follow the Curie -Weiss law only within a small temperature range (~60°C) above Curie temperature, giving a second region with smaller slope. This behaviour can be explained on the basis of the Heywang's model. The decrease of the surface states at high temperature re- sults in the narrowing of the grain boundary barrier layers.