Raman and optical absorption studies of the pressure-induced zircon to scheelite structure transformation in TbVO₄ and DyV0₄

Abstract

The pressure-induced phase transition in terbium vanadate (TbVO₄) and dysprosium vanadate (DyVO₄) from the zircon-type structure D¹⁹_4h to the scheelite-type structure C⁶_4h has been studied at room temperature by high-pressure Raman spectroscopy in a diamond anvil cell. The pressure dependencies of the Raman active modes are presented up to 18 GPa in TbVO₄ and 10 GPa in DyVO₄. From these data the transition pressures are found to be 6.6 ± 0.6 GPa for TbVO4 and 6.5 ± 0.3 GPa for DyVO₄. X-ray powder diffraction studies confirm that the high-pressure phase, quenchable in polycrystalline form to atmospheric pressure in both cases, has the scheelite-type structure. The effect of pressure on the optical absorption edge was also investigated. It is found that dE_g/dP is linear to 30 GPa, with slopes of −37 meV GPa^-1 for TbVO₄ and −33meV GPa^-1 for DyVO₄. These results are discussed in terms of the phase transition kinetics, and changes in the electronic structure both at the transition and in the scheelite-type phase.