Abstract
It has been reported that the intermediate spin state becomes the ground state of Co ions in perovskite-type cobalt oxides and that peculiar spin-crossover phenomena occur in the oxides. The experimental facts and their interpretation on the spin state and the spin crossover phenomena of LaCoO3 and Pr0.5Ca0.5CoO3 are introduced in comparison with those in spin-crossover complexes. The spin crossover phenomena of the perovskite-type cobalt oxides are correlated with the change in electrical resistivity. It has been considered that the correlation originates from the strong Co 3d eg-O2p hybridization connecting with the intermediate spin state. In addition, many facts imply that the roles of vibrational and magnetic energies to the spin-crossover phenomena are different between perovskite-type cobalt oxides and spin-crossover complexes.
