Topochemical conversion of the discontinuous-zone-axis to form bismuth titanate oriented polycrystal nanocomposites

Abstract

Bismuth titanate based materials have wide potential applications in the fields of dielectrics, piezoelectrics, ferroelectrics, catalysis and energy storage. In this study, a two dimensional (2-D) layered H_1.07Ti_1.73O₄·nH₂O (HTO) crystal was used as a precursor to prepare 2-D bismuth titanate oriented polycrystal nanocomposites using two kinds of Bi³⁺ sources. The chemical reaction mechanisms for the formation of bismuth titanates are proposed, and the crystal structures and their conversions are also identified. The formation mechanism of the discontinuous-zone-axis is revealed. The obtained bismuth titanates are oriented polycrystals constructed from the orientation nanocrystals. In the process of forming the oriented polycrystal, the zone axis of the bismuth titanates obtained under different reaction conditions can vary even if the same reactants are used in the reaction. The certain topological correspondences among the oriented polycrystal, the precursor, and the intermediate, as well as the formation of bismuth titanates with a discontinuous-zone-axis based on a topochemical mesocrystal conversion reaction, were proposed. The special arrangement structure of the TiO₆ octahedral layers accommodating in the HTO crystal is the main reason for the constant change of the zone axis of the bismuth titanate nanocomposite. However, based on the crystallographic investigation of the reaction mechanism involved in the formation process of construction of the bismuth titanate oriented polycrystal nanocomposite from the HTO crystal, it is found that the topochemical mesocrystal conversion reaction with a discontinuous-zone-axis is different from the conventional topochemical reactions. This may be attributed to the combination of the HTO matrix and Bi³⁺. It is vital to study the controllable preparation of bismuth titanate based nanocomposites and further understand the topochemical reaction.