Thermal evolution of the crystal structure of the orthorhombic perovskite LaFeO3

Abstract

The thermal evolution of the crystal structure of the prototypical orthorhombic perovskite LaFeO3 has been studied in detail by powder neutron diffraction in the temperature range 25<T<1285K. A conventional bond length/bond angle analysis, combined with an analysis in terms of symmetry-adapted modes, allows key aspects of the thermal behavior to be understood. In particular, the largest-amplitude symmetry modes (viz. in-phase and out-of-phase octahedral tilts, and A-site cation displacements) are shown to display relatively ‘normal’ behavior, increasing with decreasing temperature, which contrasts with the anomalous behavior previously shown by the derivative Bi0.5La0.5FeO3. However, an unexpected behavior is seen in the nature of the intra-octahedral distortion, which is used to rationalize the unique occurrence of a temperature dependent crossover of the a and c unit cell metrics in this compound.