Structure and physical properties ofYCoO3at temperatures up to1000K

Abstract

The crystal structure of perovskite $\mathrm{Y}\mathrm{Co}{\mathrm{O}}_{3}$ has been studied by neutron powder diffraction up to high temperatures. The orthorhombic $Pbnm$ symmetry is confirmed in the whole temperature range. A significant isotropic enlargement of $\mathrm{Co}{\mathrm{O}}_{6}$ octahedra is evidenced above $600\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ leading to unit cell expansion and increased octahedral tilting. Supported by complementary physical measurements, the origin of anomalous expansion is identified with a gradual transition of ${\mathrm{Co}}^{3+}$ ions from the diamagnetic low-spin $(S=0)$ ground state to excited magnetic states with spin $S=1$ or 2. The magnetic transition is closely followed by a broad resistivity transition of the insulator-metal type, centered at $750\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. The changes in magnetic susceptibility, electric resistivity, thermopower and thermal conductivity associated with transitions in $\mathrm{Y}\mathrm{Co}{\mathrm{O}}_{3}$ are discussed in comparison with similar data on related perovskite $\mathrm{La}\mathrm{Co}{\mathrm{O}}_{3}$.