Structural distortions in rare-earth transition-metal oxide perovskites under high pressure

Abstract

Owing to their structural complexity and wide range of possible chemical combinations, perovskite oxides exhibit many technically important physical properties. Pressure is a thermodynamic parameter which is useful for tuning physical properties; however, the response of the complex crystal structure to high pressure has not been thoroughly studied and rationalized. This study focuses on in situ high-pressure x-ray diffraction of the orthorhombic perovskite oxides ${A}^{3+}{B}^{3+}{\mathrm{O}}_{3}$, commonly found for the rare-earth transition-metal oxides of the $RM{\mathrm{O}}_{3}$ formula. Each of the four families of $RM{\mathrm{O}}_{3}$ ($M=\mathrm{Ti}$, Cr, Mn, Fe) perovskites in this study all crystallize in the same orthorhombic perovskite structure with the Pbnm space group. The lanthanide contraction in these materials leads to varying degrees of orthorhombic distortions that are primarily associated with octahedral site rotations. The pressure-induced change of the lattice parameters demonstrates an evolution from a suppression to an enlargement of the orthorhombic distortion for substitution of the rare-earth element from $R=\mathrm{La}$ to Lu in $RM{\mathrm{O}}_{3}$ perovskites. This unusual crossover of the lattice parameters' dependence on pressure contradict the results from first-principles calculation but can be rationalized by the intrinsic distortion of the perovskite structure.