Defect Structure of the High-Dielectric-Constant Perovskite Cacu3ti4o12

TL;DR

This study uses transmission electron microscopy to analyze the defect structures in CaCu3Ti4O12, revealing dislocations, cation disorder, and grain boundary defects that may explain its high dielectric response.

Contribution

It provides detailed TEM-based insights into defect structures in CaCu3Ti4O12, supporting a morphological model involving conducting and blocking regions.

Findings

High density of dislocations with Burger vector [110] in single crystals

Presence of grain boundary oxygen deficiency in polycrystalline samples

Defect structures likely contribute to the material's large dielectric response

Abstract

Using transmission electron microscopy (TEM) we studied CaCu3Ti4O12, an intriguing material that exhibits a huge dielectric response, up to kilohertz frequencies, over a wide range of temperature. Neither in single crystals, nor in polycrystalline samples, including sintered bulk- and thin-films, did we observe the twin domains suggested in the literature. Nevertheless, in the single crystals, we saw a very high density of dislocations with a Burger vector of [110], as well as regions with cation disorder and planar defects with a displacement vector 1/4[110]. In the polycrystalline samples, we observed many grain boundaries with oxygen deficiency, in comparison with the grain interior. The defect-related structural disorders and inhomogeneity, serving as an internal barrier layer capacitance (IBLC) in a semiconducting matrix, might explain the very large dielectric response of the material. Our TEM study of the structure defects in CaCu3Ti4O12 supports a recently proposed morphological model with percolating conducting regions and blocking regions.