Combining theoretical and experimental methods to study some zircon-type orthovanadates at high pressure.*

Many studies of zircon-type orthovanadates under high pressure have been performed. Some of these experiments using methanol-ethanol-water as pressure transmission medium report a zircon-to-monazite phase transition. In this work, we will focus on the study of the zircon-to-scheelite phase transition of some orthovanadates, combining high pressure experimental hydrostatic studies and ab initio simulations. Our approach provides information on the structural, electronic, dynamical, and elastic properties of these compounds. From our simulations, we found that around the transition pressure the zircon phase becomes dynamically unstable due to the softening of one B_1u silent mode. Our study of the elastic constants and the analysis of the generalized mechanical stability criteria show a mechanical instability also appears near the transition pressure. We will also report on the new high pressure phase that appear after the zircon-to-scheelite transition.