Formation kinetics and thermodynamic stability of the Aurivillius compounds in Bi4Ti3O12–BiFeO3 system

Abstract

AbstractThe Aurivillius compounds in the Bi2O3–Fe2O3–TiO2 system, combining ferroelectric, semiconducting, and ferromagnetic properties, have attracted particular interest. Formation kinetics and thermodynamic stability are the fundamental knowledge needed for modeling and predicting the temporal microstructure and property evolution during materials processing but have not yet been addressed by quantitative experimental measurement. This article focuses on the Bin+1Fen–3Ti3O3n+3 Aurivillius compounds on the Bi4Ti3O12–BiFeO3 tie‐line to elucidate the mechanisms and thermodynamic controls responsible for phase formation of compounds with various perovskite‐like layers. Five high‐purity Aurivillius compounds Bi4Ti3O12, Bi5FeTi3O15, Bi6Fe2Ti3O18, Bi7Fe3Ti3O21, and Bi8Fe4Ti3O24 with integer n = 3–7 values were synthesized and their phase transformation properties and enthalpies of formation were studied by X‐ray diffraction in situ, high temperature differential scanning calorimetry, and high temperature oxide melt solution calorimetry. Thermodynamic stability of the compounds decreases with increasing n, and formation kinetics gradually slow down, demonstrating the inherent difficulty to synthesize pure Aurivillius compounds with n larger than 8. This difficulty was confirmed by an impurity phase coexisting with Bi9Fe5Ti3O27.