Amorphization and structural evolution of αα-HfMo2O8HfMo2O8 and its high density polymorph ββ-HfMo2O8HfMo2O8 at high pressures

The high pressure and high temperature structural investigations on αα and ββ phases of HfMo2O8HfMo2O8 are reported. αα-HfMo2O8HfMo2O8 transforms to a monoclinic (δδ) phase, followed by a second transition to a triclinic (εε) phase at 1.30(5) and 2.70(5) GPa, respectively. αα-HfMo2O8HfMo2O8 undergoes pressure induced amorphization above 24 GPa due to kinetically hindered phase transition to its high density polymorph ββ phase. The ββ-HfMo2O8HfMo2O8 also undergoes a complete pressure induced amorphization above 35 GPa due to the kinetic hinderance to decomposition. When annealed at ambient pressure, ββ-HfMo2O8HfMo2O8 reconverts to the trigonal αα phase above 700 °C.