Experimental and Theoretical Study of Zircon and Scheelite Phases of DyVO₄

Abstract

Polycrystalline zircon-type dysprosium orthovanadate, DyVO4, prepared from a single crystal grown by slow cooling from PbO/PbF2 ux, was studied by X-ray diraction. Rietveld renement provided the following unit cell size and oxygen atom coordinates: a = 7.14811(4) Å; c = 6.30825 (4) 2082(4) which are of a particularly high accuracy and show consistency with earlier reported values. Density functional theory calculations within the generalized gradient approximation for the exchange-correlation energy were also performed, providing values of structure parameters which dier by less than 2% from the experimental ones. The agreement between theory and experiment demonstrates the value of these calculations for understanding the structure of compounds of RVO4 family. In addition, density functional theory calculations were performed for the scheelite-type DyVO4; also for this polymorph the discrepancy with the only known set of lattice parameters is less than 2%. Values of oxygen atom coordinates have not been reported yet for this polymorph; here, the calculated ones are quoted.

Equation of state of zircon- and scheelite-type dysprosium orthovanadates: a combined experimental and theoretical study

“…With regard to the oxygen atomic position, at ambient pressure the theoretical coordinate values are in good agreement with those obtained from powder diffraction experiment [47]. Note that the present ab initio calculations provide the first report on the dependence of the oxygen position on pressure for DyVO 4 .…”

“…It is noteworthy that for some zircon-type RVO 4 crystals a trace amount of the scheelite-type phase has been reported to be formed during grinding of the zircon-type phase (see, e.g., [17]), but this phenomenon is not observed in the present study. The Rietveld refinement study based on the mentioned data provided accurate values of lattice parameters, a = 7.148 11(4) Å and c = 6.308 25(4) Å, with a unit cell volume V = 322.323 (3) Å3 , and refined atomic coordinates for O: y = 0.4300(4) and z = 0.2082(4) [47].…”

“…Phase analysis performed for laboratory powder x-ray diffraction data showed that the DyVO 4 crystal (the same as sample A) is a single phase of zircon type [47]. It is noteworthy that for some zircon-type RVO 4 crystals a trace amount of the scheelite-type phase has been reported to be formed during grinding of the zircon-type phase (see, e.g., [17]), but this phenomenon is not observed in the present study.…”