Raman and optical absorption studies of the pressure-induced zircon to scheelite structure transformation in TbVO 4 and DyV0 4

Abstract

The pressure-induced phase transition in terbium vanadate (TbVO 4) and dysprosium vanadate (DyVO 4) from the zircon-type structure D 19 4 h to the scheelite-type structure C 6 4 h 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 TbVO 4 and 10 GPa in DyVO 4. From these data the transition pressures are found to be 6.6 ± 0.6 GPa for TbVO 4 and 6.5 ± 0.3 GPa for DyVO 4. 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 d E g /d P is linear to 30 GPa, with slopes of −37 meV GPa -1 for TbVO 4 and −33meV GPa -1 for DyVO 4. 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.