Temperature-Driven Multiferroic Phase Transitions and Structural Instability Evolution in Lanthanum-Substituted Bismuth Ferrite

Structural phase transition behavior of a material under temperature plays a key role in understanding its physical properties, instabilities, and design of new functions. However, there is extreme shortage of investigations on the temperature-driven phase transition behaviors of bismuth ferrite (BiFeO3). Herein, magnetic phase transitions within low-temperature regimes, ferroelectric phase transitions under high temperature, structural instability evolution, and spin-phonon coupling in 5% La-doped BiFeO3 ceramic (BFLa05) were systemically studied by employing X-ray diffraction, differential scanning calorimetry, Raman spectroscopy, and magnetic measurement, as well as the phenomenological theoretical analysis. Thanks to the outstanding stability of BFLa05 ceramic under high temperature, a complete phase transition sequence of α ↔ β ↔ γ was observed, simultaneously determining the crystalline symmetries for β and γ phases as orthorhombic Pnma and cubic Pm3m, respectively. Octahedral tilt as a typical str...