Dielectric properties correlation with microstructure in ABi4Ti4O15 (A = Sr, Ba) bismuth layered ferroelectrics

Abstract

The bismuth layered ferroelectrics (BLFs) BaBi₄Ti₄O₁₅ and SrBi₄Ti₄O₁₅ were synthesized using solid-state-reaction technique and the impact of ‘thermal etching’ on their microstructure and dielectric and ferroelectric properties was thoroughly investigated. The phase formation and crystallization to the orthorhombic A2₁am phase was confirmed by XRD followed by Rietveld refinement. The thermally etched compounds depict the formation of highly uniform plate-like grain distribution with a reduced grain size. The effect of improved microstructure was also evident in the dielectric properties with a colossal change in the dielectric constant, ε′. Furthermore, the study suggests that the ferroelectric polarization can also be improved by thermal etching, reducing the contribution due to non-ferroelectric components. The impedance analysis using a brick-layer model shows that impedance is predominantly due to grains (bulk) with a relatively small contribution due to grain boundaries in these BLFs. The observed change in macroscopic properties was attributed to the modification in grain–grain boundary configuration post thermal etching.