A high-pressure Raman study of yttrium vanadate (YVO 4) and the pressure-induced transition from the zircon-type to the scheelite-type structure

Abstract

The pressure dependences of the Raman active modes in yttrium vanadate (YVO 4) crystallizing in the zircon-type structure D 4 h 19 ( I4 1 amd ), have been studied using a diamond anvil cell up to 15 GPa. At room temperature the zircon-type structure transforms to the scheelite-type structure C 4 h 6( I4 1 a ) with a = 5.04 Å and c = 11.24 Å near 7.5 GPa. The density changes from 4.24 to 4.74 g cm 3 in the transition, and the corresponding volume decrease is Δ V = 5.07 cm 3 mole . The high-pressure phase is retained on release of pressure. The optical absorption edge shifts from 3.87 to 2.77 eV at the transition, presumably due to charge transfer, or due to V-O bond length change of the VO 4 tetrahedra. The internal mode frequencies of the VO 4 tetrahedra also decrease abruptly at the transition. The V-O bond stretching frequency decreases from 891 to 828 cm −1 in the scheelite-type phase, which suggests a fundamental change in the VO 4 unit. The general question of the stability of the zircon-type structure under high pressure is discussed in the light of the high-pressure behavior of a large number of rare earth vanadates and arsenates.