Spin Crossover Phenomena in $\mathrm{SmCo}_{0.5}\mathrm{Ga}_{0.5}\mathrm{O}_{3}$

Abstract

Single-phase samarium cobaltite-gallate $\mathrm{SmCo}_{0.5}\mathrm{Ga}_{0.5}\mathrm{O}_{3}$ with the orthorhombic Pbnm perovskite structure was synthesized for the first time by solid state reactions technique. No symmetry-related structural changes were observed in a broad temperature range of 310–1100 K by using in situ X-ray synchrotron powder diffraction. The temperature-dependent synchrotron powder diffraction measurements of $\mathrm{SmCo}0.5 \mathrm{Ga}_{0.5}\mathrm{O}_{3}$ revealed pronounced deviation from a “normal” lattice expansion, which are manifested in nonmonotonic temperature dependence of the unit cell dimensions and abnormal increase of thermal expansion coefficients with broad maxima near 780 K. These anomalies, as well as detectable deviations in the temperature dependencies of the intraoctahedral bond length and octahedra tilt angles are associated with the temperature induced spin state transitions of Co3+ and coupled insulator-metal transitions occurred in $\mathrm{SmCo}_{0.5}\ \mathrm{Ga}_{0.5}\ \mathrm{O}_{3}$ at the elevated temperatures.