Structural transformation in Mn-substituted Sr2Bi2Ta2TiO12 Aurivillius phase synthesized by hydrothermal method: A comparative study and dielectric properties

Abstract

In this study, a hydrothermal method was applied to synthesize the three-layer Aurivillius phase Sr2Bi2Ta2TiO12 (SBTTO) and Mn-substituted Sr1·5Bi2·5Ta2Ti0·5Mn0·5O12 (SBTTMO), with the use of NaOH as a mineralizer. The crystal structure, morphology, dielectric properties, and the correlation between the structural transformation and dielectric properties were investigated. The XRD data reveal that the SBTTO sample adopts a tetragonal crystal structure with the I4/mmm space group and is then transformed into an orthorhombic structure with the B2cb space group for SBTTMO. The morphology of both samples was observed by SEM, which showed anisotropic plate-like grains. With the Mn substitution, the ferroelectric transition temperature (Tc) significantly increases as the influence of the 6s2 lone pair of Bi3+ increases, and this in turn further induces the relaxor-ferroelectric behavior. Consequently, the increase in Tc confirms the structural transformation from the paraelectric-tetragonal to the ferroelectric-orthorhombic phase.