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 Fd3¯m structure to tetragonal I41/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 K0 = 189(2) GPa, K0′=7.2(3) and V0 = 578.68(4) Å3, consistent with theoretical calculations. The EOS of the high pressure tetragonal phase was also obtained as K0 = 191(8) GPa and V0 = 279(1) Å3 when K0′ = 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.

► Both Raman and X-ray diffraction data show a phase transition for magnesiochromite (MgCr2O4) at about 20 GPa.
► A distorted spinel structure (I41/amd) was found for the high pressure phase of MgCr2O4.
► The equations of state of both low and high pressure phases were determined.