Structural aspects in A-site ordered perovskite CaCu3Ti4O12: Colossal dielectric behavior and Ca/Cu disordering

Precise analysis of crystal structure of A-site ordered perovskite CaCu3Ti4O12 was studied at 298, 517 and 785 K, where Ca/Cu disordering is taken into account. The ratio of Ca/Cu disordering is 11% at 785 K, which decreases to 1.7 % at 298 K with decreasing temperature. This Ca/Cu dynamical disordering produces meta-stable intermediate atomic configurations which force to have a polar structure for TiO6 octahedra. This structural heterogeneity may induce an instantaneous dipolar fluctuations and results in a colossal dielectric response, while the average stable state is non-polar.