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

The pressure dependence of the Raman active modes in yttrium vanadate (YVO sub 4) crystallizing in the zircon-type structure D 19 above 4h (I4 sub 1 / amd), has been studied using a diamond anvil cell up to 15 GPa. At room temperature the zircon-type structure transforms to the scheelite-type structure C6 above 4h (I4 sub 1 / a) with a=5.04angstroms and c=11.24angstroms near 7.5 GPa. The density changes from 4.24 gm/cc to 4.74 gms/cc in the transition, and the corresponding volume decrease is DELTA V = 5.07 cc/mole. The high pressure phase is retained on release of pressure. The optical absorption edge shifts from 3.87eV to 2.77eV at the transition, presumably due to charge transfer, or due to V-O bond length change of the VO sub 4 tetrahedra. The internal mode frequencies of the VO sub 4 tetrahedra also decrease abruptly at the transition. The V-O bond stretching frequency decreases from 891 cm sup (-1) to 828 cm sup (-1) in the scheelite-type phase, which suggests a fundamental change in the VO sub 4 unit.