LAUSR

Crystal and electronic structure of ${\mathrm{Co}}_{3}{\mathrm{O}}_{4}$ spinel have been investigated by x-ray absorption near edge structure (XANES) at the Co $K$ edge up to 58.5 GPa and Raman scattering up to 65 GPa. Several transitions have been observed upon pressurization, and the original structure was recovered on decompression. Experimental and theoretical XANES and Raman data are compatible with the occurrence of a monoclinic $P{2}_{1}/c$ phase above $\ensuremath{\sim}52.7$ GPa. Vibrational modes analyzed in details by Raman scattering indicate that two other subtle transitions take place above $\ensuremath{\sim}21.9$ GPa (orthorhombic $Fddd$) and $\ensuremath{\sim}43.0$ GPa (monoclinic $C2/m$), in agreement with the previous x-ray diffraction experiments. Our combined experimental XANES and multiple scattering calculations indicate clear evidence of a tetrahedral to octahedral coordination crossover at the ${\mathrm{Co}}^{2+}$ sites, being completed upon transition to the monoclinic $P{2}_{1}/c$ phase. The valence and spin states at two different $\mathrm{Co}$ sites remained unchanged at least up to the transition onset to the monoclinic $P{2}_{1}/c$ phase ruling out the possibility of charge transfer and spin crossover in the intermediate phases as proposed previously.