Compression tuned crystalline and amorphous phases of Gd2Si2O7: Raman spectroscopic and first-principles studies

Abstract

Compounds that have polymorphism at ambient conditions exhibit interesting structural transitions under different thermodynamic conditions. The compound Gd2Si2O7 is an interesting silicate that exhibits polymorphism at ambient conditions. We have investigated high pressure behavior of orthorhombic Gd2Si2O7 using Raman spectroscopy and identified structural changes at pressures 2 and 8 GPa followed by transformation to a disordered/glassy phase above 13 GPa. While the transitions are reversible from 12 GPa, releasing from higher pressures leads to recovery of a glassy phase. We have carried out density functional theory (DFT) simulations for the high-pressure structural optimization of the different phases of Gd2Si2O7. The enthalpy cross over as obtained from DFT simulations predicts the high-pressure phase above 2 GPa to be triclinic and the phase above 8 GPa to be monoclinic Gd2Si2O7 which support the experimental findings. The random change of Si-O bond length above 20 GPa points towards possible amorphization for the monoclinic phase.