We present the study of the structural changes of cobalt oxide ${\text{Co}}_3{\text{O}}_4$ under high pressure. At room temperature and atmospheric pressure, ${\text{Co}}_3{\text{O}}_4$ crystallizes in a cubic $Fd-3m$ structure. We found that within the pressure range 0–60 GPa the system undergoes three phase transitions, which take place at 23, 45, and 52 GPa. In the first one, the original cubic structure distorts to an $Fddd$ orthorhombic lattice. At 45 GPa, a first order phase transition induces a distortion to a monoclinic phase with $C2/m$ space group and a volume per formula unit reduction of 4%. This phase has not been reported in the literature previously. Finally, at 52 GPa the orthorhombic phase disappears and a phase transition towards the formation of $P{2}_1/c$ crystal structure is evidenced. This last phase coexists with the $C2/m$ phase up to 55 GPa. From the diffractograms measured at 57 GPa it was possible to solve the structure of the $P{2}_1/c$ phase. Results showed the layered character of the structure and a change in the ${\mathrm{Co}}^{+2}$ coordination number from 4 to 6.

• Received 3 May 2019
• Revised 2 August 2019

DOI:https://doi.org/10.1103/PhysRevB.100.054111