Hydrothermal synthesis of ABi2Ta2O9Aurivillius phase: A comparative study of A-site cation size on structure, dielectric, optical properties

Abstract

In this study, the double-layered Aurivillius phases CaBi2Ta2O9 (CBT) and PbBi2Ta2O9 (PBT) were prepared through a hydrothermal route with NaOH as a mineralizer. XRD analysis confirmed that the CBT and PBT compounds were successfully formed and adopted an orthorhombic crystal structure with an A21am symmetry. Le Bail refinements of XRD data indicated that the unit cell volume of CBT was smaller than PBT and is associated with the smaller ionic radius of Ca2+ compared to Pb2+. The surface morphology of both samples, as determined using SEM, demonstrated plate-like grains with anisotropic grain growth. It was found that the different ionic radii of A-site cations (Ca2+ and Pb2+) strongly affected the structural, optical and electrical properties of the Aurivillius phase. The occupation of smaller Ca2+ cations induced a higher structural distortion, which resulted in higher bandgap (Eg) energy and ferroelectric transition temperature (Tc) of CBT, compared to those of PBT.