Is the oxide La2Ba2Cu2Ti2O11 a layered perovskite? Effect of treatment on the concentration of defects and distortion of order

Abstract

A layered structure is the thermodynamically stable form of the perovskite Ln2Ba2Cu2Ti2O11 (Ln = La) prepared at 1100°C. But contrary to other derivatives with Ln = Nd-Tb variable degrees of order/disorder associated with the concentration of defects can be detected depending on the extension of the synthetic treatments. This oxide was prepared by the ceramic method with varying reaction times. Electron diffraction and HRTEM show the presence of an ap × ap × 4ap layered perovskite superstructure with a high concentration of defects in samples prepared during 48 h. Longer reaction times (11 days) result in a higher degree of order and a better defined superstructure. For samples reacted during 17 days the order is complete and identical to that found for other related derivatives such as Ln2Ba2Cu2Ti2O11 (Ln = Nd, Eu, Tb).