High pressure Raman spectroscopic study of spinel MgCr 2 O 4

An in situ Raman spectroscopic study was conducted to investigate the pressure induced phase transformation of MgCr2O4 spinel up to pressures of 76.4 GPa. Results indicate that MgCr2O4 spinel undergoes a phase transformation to the CaFe2O4 (or CaTi2O4) structure at 14.2 GPa, and this transition is complete at 30.1 GPa. The coexistence of two phases over a wide range of pressure implies a sluggish transition mechanism. No evidence was observed to support the pressure-induced dissociation of MgCr2O4 at 5.7-18.8 GPa, predicted by the theoretical simulation. This high pressure MgCr2O4 polymorphism remains stable upon release of pressure, but at ambient conditions, it transforms to the spinel phase