Pressure-induced phase transition study of magnesiochromite (MgCr2O4) by Raman spectroscopy and X-ray diffraction

Pressure-induced phase transition in magnesiochromite (MgCr2O4) was studied by in situ Raman spectroscopy and X-ray diffraction to 50 and 60 GPa, respectively. A polymorphic phase transition from cubic Fd (3) over barm structure to tetragonal I4(1)/amd structure was observed at pressures above 20 GPa and this transition is complete at 23.5 GPa. The volume data for magnesiochromite fitted to Birch-Murnaghan equation of state (EOS) yield K-0 = 189(2) GPa, K-0', = 7.2(3) and V-0 = 578.68(4) angstrom(3), consistent with theoretical calculations. The EOS of the high pressure tetragonal phase was also obtained as K0 = 191(8) GPa and V-0 = 279(1) angstrom(3) when K-0', = 4 (fixed). The volume reduction at phase transition is about 4.4%. The high pressure phase is unquenchable and transformed back to magnesiochromite with little hysteresis upon release of pressure. (C) 2012 Elsevier B.V. All rights reserved.