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(2g)(5)e(g)(1) to a nonmagnetic low-spin ground state t(2g)(6) in LaCoO3 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 4.8x10(-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 Co3+ cation.