Phase transition of hafnon, HfSiO4, at high pressure

Abstract

AbstractThe high‐pressure behavior of hafnon has been systematically investigated by combining in situ synchrotron X‐ray diffraction, Raman, high‐resolution transmission electron microscopy (HRTEM) techniques, and theoretical simulations. Hafnon starts phase transition at 26.6 GPa and completes the transition to an irreversible scheelite phase (, Z = 4, a0 = 4.712 Å, and c0 = 10.378 Å) at ∼45 GPa. The HRTEM observation of an interface between hafnon and scheelite phases allows atomic scale understanding of the transition process with a relationship of (200)h‖(112)s, //, and . Hafnon shows a significantly lower transition pressure (∼12.6 GPa), as calculated from the relative enthalpies, than the measured pressure (∼26 GPa), indicating a kinetically hindered process involved in the transition. A high pressure low symmetry phase in hafnon () is identified by the simultaneous appearance of two Raman modes (∼75 and 450 cm−1) at 26.6 GPa and their subsequent simultaneous disappearance at 36.7 GPa. These results are important to understanding the mechanism of the zircon‐scheelite transition for both zircon and hafnon.