Stoichiometry, Stability and Phase Equilibria of CaCu3Ti4O12 (CCTO) High Permittivity Ceramics

目前人们对CaCu3Ti4O12、CCTO、陶瓷的电学性能非常感兴趣，因为它们是具有半导体晶芯和绝缘晶或畴边界的非均质材料，这取决于它们的制造方法。这种不寻常的电微观结构产生了与绝缘区域的几何尺寸相关的非常高的有效介电常数，以及在电陶瓷中应用的可能性，例如，一种新型电容器材料。对CCTO的科学兴趣仍在继续，特别是要了解电非均质性的原因，并通过成分控制或掺杂来改变其性质。本提案旨在阐明CCTO材料科学的四个基本特征：第一，它的真正化学计量，因为有相当多的证据表明它要么是非化学计量的，要么存在于一系列阳离子组成中；其次，它的高温稳定性，特别是它的熔化行为，以及在这之前是否会从晶格中损失Cu2O；其三，其固有的电学性质作为温度和大气的函数，特别是，从活化跳变到局域电子运动随温度降低的转变性质和这种现象对组成的依赖；第四，控制其陶瓷微观结构的因素，特别是某些样品在烧制过程中出现的导致双相结构的异常晶粒生长。鉴于对CCTO性能的持续极大兴趣，这项基础材料科学研究对于提供基础信息以允许以各种形式制造CCTO并优化其性能控制至关重要。

There is much current interest in the electrical properties of CaCu3Ti4O12, CCTO, ceramics, since they are, depending on their method of fabrication, heterogeneous materials with semiconducting grain cores and insulating grain or domain boundaries. This unusual electrical microstructure gives rise to a very high effective permittivity associated with the geometric dimensions of the insulating regions and the possibility of applications in electroceramics as, for instance, a novel capacitor material. Scientific interest in CCTO continues, in particular to gain understanding of the reasons for the electrical heterogeneity and to modify its properties by compositional control or doping. This proposal aims to clarify four basic features of the materials science of CCTO: first its true stoichiometry since there is considerable evidence that it is either non-stoichiometric or exists over a range of cation compositions; second, its high temperature stability and in particular, its melting behaviour and whether or not this is preceded by loss of Cu2O from the crystal lattice; third, its intrinsic electrical properties as a function of temperature and atmosphere, and in particular, the nature of the transition from activated hopping to localised electron motion with decreasing temperature and the dependence of this phenomenon on composition; fourth, the factors that control its ceramic microstructure and in particular, the occurrence of anomalous grain growth leading to a duplex structure on the firing of certain samples. Given the continuing great interest in the properties of CCTO, this fundamental material science study is essential to provide underpinning information to allow the fabrication of CCTO in various forms and to optimise control of its properties.