存在晶型转变的TiO2陶瓷的空间电荷偏析、势垒结构与老化性能

The degradation of TiO2 varistor ceramics are mainly caused by lower barrier height and higher Leakage current, which are induced via point defects complex and space charge migration in depletion layer at grain boundaries. Currently, relevance between the anatase to rutile crystallographic transformation（ARCT）and space charge segregation at grain boundaries is not researched systematically. In the project，promotion and inhibition of ARCT ,segregation mechanism of space charge，variation law of barrier structre and a method to improve aging properties are studied by a combination experients and theoretical calculation. . TiO2 ceramics samples are prepared by a traditional solid-state sintering method. Effects of sintering temperature and atmosphere on point defects concentration, ARCT, space charges segregation trend at grain boundaries, microstructure, barrier structure and aging properties of undoped, single-doped and codoped TiO2 ceramics are discussed. Segregation mechanism of space charge, chemistry defects principles of pore in TiO2 grains derived from oxygen vacanxies and formation mechanism of secondary phases are studied by material test techniques and point defects thermodynamic method.The barrier structure are calculated based on the electrical properties and thermoelectric emissions theory. Effects of temperature,time and electric field on degradation，barrier structure and space charge migration are investigated.Effect of crystallographic transformation on space charges segregation and grain boundaries barrier strcuture in TiO2 ceramic are also explored.

TiO2压敏陶瓷的老化主要是由晶界耗尽层中空间电荷的迁移、点缺陷复合引起势垒高度降低，漏电流增加所引起。目前，空间电荷的晶界偏析与锐钛矿向金红石结构的晶型转变（ARCT）的关联性缺乏系统研究。本项目将实验和理论计算相结合，研究ARCT的促进和抑制机理、空间电荷的晶界偏析机理、势垒结构的变化规律和改善老化特性的方法。 . 采用传统固相烧结工艺制备TiO2样品，研究烧结温度和气氛对不掺杂、单掺杂、共掺杂TiO2陶瓷的点缺陷的浓度、空间电荷晶界偏析趋势、ARCT、显微结构、势垒结构和老化特性的影响。由结构检测和点缺陷热力学研究空间电荷的偏析机理、氧空位形成晶粒内气孔的缺陷化学原理、第二相形成机制。基于电学性能和热电子发射理论计算势垒结构。考查样品在温度、时间和电场作用下的老化特性和空间电荷的迁移规律，ARCT对空间电荷偏析和晶界势垒结构的影响。

TiO2作为一种重要的功能材料，其相变机理及其影响TiO2晶型转变的因素，晶型对于TiO2材料的光催化性能和TiO2陶瓷的压敏性能的影响都是影响TiO2应用领域的重要因素之一。本项目研究了TiO2的本征缺陷和点缺陷的形成能，确定了各点缺陷对于电子结构的贡献，研究表明：氧空位是TiO2中的主要缺陷之一，并研究了不同氧空位浓度对于电子结构的影响。研究了掺杂TiO2的键合特征，表明Cu掺杂TiO2中存在取代固溶掺杂和间隙固溶掺杂。采用第一性原理计算了La，Nb单掺杂和共掺杂的晶界偏析能，结果表明：La掺杂偏析趋势明显。XRD和EDS检测表明:La大量在晶界偏析然后形成第二相。第二相对TiO2陶瓷的显微结构、势垒结构和老化性能有明显的影响。不同金属离子掺杂对于TiO2粉体和TiO2压敏陶瓷的物相组成、形貌和性能均有明显的影响。晶型转变对于（Bi，Nb）掺杂TiO2压敏陶瓷的第二相的形成和掺杂离子在晶界的偏析有明显影响。（Bi，Nb）掺杂金红石TiO2压敏陶瓷具有较为稳定的晶界势垒结构，这主要是稳定的金红石结构导致TiO2晶格中Nb固溶降低和增加了Bi在晶界偏析趋势所致。