PRESSURE-INDUCED INTERMEDIATE-TO-LOW SPIN STATE TRANSITION IN LACOO3

Synchrotron x-ray powder-diffraction experiments reveal that the transition from a magnetic intermediate spin (IS) state t 5 2ge 1 g to a nonmagnetic low-spin ground state t 6 2g in LaCoO 3 normally observed when cooling manifests itself under pressure by an anomalously low bulk modulus of 150(2) GPa and an initially very large Co-O bond compressibility of 4.8×10 - 3 GPa - 1 which levels off near 4 GPa. The continuous depopulation of the IS state is driven by an increased crystal-field splitting resulting in an effective reduction of the size of the Co 3 + cation.