Phase stability of YbVO4 under pressure: In situ x-ray and Raman spectroscopic investigations

Abstract

The phase stability of YbVO4 under pressure has been investigated using synchrotron based angle dispersive x-ray diffraction and Raman spectroscopic techniques up to 34.5 and 26.5 GPa, respectively. The results indicate that the compound transforms from the ambient pressure zircon structure to the scheelite structure above 5.9 GPa with 11.8% volume discontinuity. The coexistence of the two phases is observed over a large pressure range. At 15.8 GPa, the (011) peak of the scheelite phase develops asymmetry, and the pattern at further high pressures could be fitted to a fergusonite-type monoclinic structure. On reducing the pressure, the fergusonite phase reverses back to the scheelite phase; the latter phase could be recovered as a metastable phase at ambient pressure. The refined structural parameters along with the equation of state are given for various phases of YbVO4. Changes in the vibrational properties across these transitions, particularly across the scheelite↔fergusonite transition, have been investigated using Raman spectroscopy.

In situhigh-pressure synchrotron x-ray diffraction study of CeVO4and TbVO4up to 50 GPa

“…Orthovanadates with small A cations have been observed to undergo an irreversible zircon-to-scheelite (space group: I4 1 /a, Z = 4) phase transition [3]. In some compounds like LuVO 4 and EuVO 4 a second transition induced by pressure has been detected. The second transition is from the tetragonal scheelite-type structure to a monoclinic fergusonite-like structure (space group: I2/a, Z = 4).…”

“…However, in CeVO 4 , a compound with a large rare-earth cation, a different structural sequence has been observed. According with Raman experiments, under compression CeVO 4 transforms from zircon to monazite under quasi-hydrostatic conditions [4]. In contrast under non-hydrostatic conditions the zircon-to-scheelite transition has been detected.…”

“…Both factors deserve to be further studied into detail. Here, in order to shed more light on the understanding of the mechanical and structural properties of zircon-type oxides, we report in situ highpressure (HP) room-temperature (RT) x-ray diffraction studies of TbVO 4 and CeVO 4 up to a pressure of 50 GPa using neon (Ne) to create quasi-hydrostatic conditions. The present work contributes to deeper the understanding of pressure effects on the crystal structure of zircon-type oxides of both technological and geophysical importance.…”

“…The main potential applications include host matrices for immobilization of certain types of radioactive wastes. The rare-earth orthovanadates AVO 4 (where A is a lanthanide) crystallize in the tetragonal zircon-type structure (space group: I4 1 /amd, Z = 4) at ambient conditions [1], with exemption of dimorphic LaVO 4 , which has a zircon-type structure or a monoclinic monazite-type structure (space group: P2 1 /n, Z = 4) depending on the mode of preparation [2]. In the zircon structure, the vanadium atom is tetrahedrally coordinated, while the trivalent lanthanide is coordinated by eight oxygen atoms, forming a bidisphenoid.…”

“…During the last decade, intensive investigations have been carried out on the structural evolution of the zircon-type vanadates under extreme conditions. In particular, x-ray diffraction [3 -6], optical [7,8], and Raman scattering measurements [4,6,8,9,10], and theoretical calculations [5,6,10,11] have been carried out to understand the structural modifications induced by pressure. Orthovanadates with small A cations have been observed to undergo an irreversible zircon-to-scheelite (space group: I4 1 /a, Z = 4) phase transition [3].…”