Novel pressure-induced phase transitions in Co3O4

Co3O4 represents an intriguing strongly correlated system since it is a spin liquid originating from A-site magnetic frustration. We conducted in-situ high pressure synchrotron x-ray diffraction experiments on Co3O4, and found two new monoclinic phases with the P121/c1 and C12/m1 structures. These high pressure phases are distinct from the high pressure structures that were previously reported for other 3d transition metal spinel oxides. The charge transfer does not drive the normal spinel to transform into a symmetry equivalent inverse spinel, and instead we observe transformations into the new monoclinic phases which have two distinct Co2+ and Co3+ octahedral sites.