Perovskite phase formation in pure and Sm- and La-substituted BiFeO ₃ thin films in isothermal and non-isothermal regimes

The prototype bismuth ferrite (BiFeO₃) has been considered a promising multiferroic material for next-generation devices due to its singular features. Still, several critical challenges that have not yet been overcome prevent its full implementation in commercial technologies. The kinetics of BiFeO₃ phase growth in thin films and the effects of trivalent rare earth substitution on the dynamics of phase formation in this system are among the important subjects to be studied. The present work reports a study on the phase formation kinetics in pure BiFeO₃, samarium-substituted BiFeO₃ (Bi_0.9Sm_0.1FeO₃), and lanthanum-substituted BiFeO₃ (Bi_0.9La_0.1FeO₃) thin films in isothermal and non-isothermal regimes using X-ray diffraction as an investigative tool. Pure BiFeO₃ was the first system to form the perovskite phase, followed by Sm-BiFeO₃ and La-BiFeO₃ films, indicating that the rare-earth cations influence the perovskite formation, and La³⁺ is the most effective at delaying the phase formation. The perovskite phase fractions formed as a function of the temperature of different samples were fitted using fourteen appropriate theoretical kinetic models. The data from the pure BiFeO₃ films were best fitted with the second-order model, while the third-order model resulted in better fits for the Sm- and La-substituted thin films. The activation energies determined through the Arrhenius relation were the lowest for pure BiFeO₃ films and the highest for La-BiFeO₃ films. The obtained results indicate that the transition of kinetic models along the system is due to the stoichiometry around the concentrations of the compound used in the synthesis.