Orthovanadates have recently emerged as promising optical materials for birefringent solid-state laser applications. They can be also used in a number of applications including cathodoluminescent materials, thermophosphors, scintillators, and nuclear waste storage. Given the technological importance of zircon-type orthovanadates, their electronic and optical properties have been extensively studied but their mechanical properties, which are of interest in several areas of materials research, are less well known. Scientists from Universidad de Valencia have been using the extreme conditions beamline at Diamond to study the structure of several zircon-type orthovanadates at high pressures and see how these change under compression. This work has been published in Physical Review B.
The group carried out room temperature angle-dispersive x-ray diffraction measurements on zircon-type EuVO4, LuVO4, and ScVO4 up to pressures of 27 GPa. Previous structural studies have shown that both YVO4 and LuVO4 orthovanadates experience a phase transition from a zircon-type structure to a scheelite-type structure at around 8.5 GPa. For LuVO4 a second transition was also observed at 16 GPa, to a monoclinic fergusonite-type structure. This experiment aimed to establish whether this sequence of zircon – scheelite – fergusonite transitions could be generalised for zircon-type oxides under high pressure.
|Structural reordering of orthovanadates|
In all the three compounds there was evidence of a pressure-induced structural phase transformation from zircon to a scheelite-type structure. The onset of the transition is near 8 GPa, but the transition is sluggish and there appears to be a coexistence region for the low- and high-pressure phases of up to 10 GPa in all three materials. In EuVO4 and LuVO4 a second transition to a M-fergusonite-type phase was found near 21 GPa. The equations of state for the zircon and scheelite phases were also determined. Among the three studied compounds, ScVO4 was found to be less compressible than EuVO4 and LuVO4, being the most incompressible orthovanadate studied to date.
This study contributes to a deeper understanding of pressure effects on the crystal structure of zircon-type oxides of both technological and geophysical importance. Daniel Errandonea led the study.
“By squeezing orthovanadates at pressures hundred of thousand times greater than atmospheric pressure we tested their structural and mechanical properties. Our experiments confirmed that pressure induces a gradual lowering of symmetry (zircon-scheelite-fergusonite structural sequence). This finding, and the accurate characterization of the role played by different atomic bonds upon compression, offer insight in the compressibility and structural stability of orthovanadates. We hope this will lead to a better understanding of the physical properties of other minerals having the same geometric structural arrangement – e.g. orthosilicates, orthophosphates, and orthoarsenates."
Daniel Errandonea, Universidad de Valencia
High-pressure structural investigation of several zircon-type Orthovanadates, D. Errandonea, R. Lacomba-Perales, J. Ruiz-Fuertes, A. Segura, S. N. Achary and A. K. Tyagi Physical Review B, Volume 79 (18), 184104, May 2009
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