PRESSURE-INDUCED AMORPHIZATION OF GD2(MOO4)3 - A HIGH-PRESSURE RAMAN INVESTIGATION

High pressure Raman spectroscopic studies on Gd2(MoO4)3(GMO) have been carried out at ambient temperature in the diamond cell to 10 G Pa hydrostatic pressure. These experiments have revealed pressure-induced phase transitions in GMO near 2GPa and 6.0 GPa. The first transition is from Pba2(beta') phase to another undetermined crystalline phase, designated as phase II, and the second transition is to an amorphized state. On releasing pressure there is a partial reversion to the crystalline state. The Raman data indicate that the amorphization is due to disordering of the MoO4 tetrahedral units. Further, it is inferred from the nature of the Raman bands in the amorphized material that the Mo-O bond lengths and bond angles have a range of values, instead of a few set values. The results of the present study as well as previous high pressure-high temperature quenching experiments strongly support that pressure-induced amorphization in GMO is a consequence of the kinetically impeded beta to alpha phase transition. The system in frustration becomes disordered. The rare earth trimolybdates crystallizing in the beta' structure are all expected to undergo similar pressure-induced amorphization.