High pressure phase transitions in BaWO4

Abstract

Using in-situ angle dispersive X-ray diffraction, we have shown that barium tungstate, which exists in scheelite phase at ambient conditions, transforms to a new phase at , 7^0.3 GPa. Analysis of our data based on Le Bail refinement suggests that this phase could be fergusonite and not HgMoO 4 type, which was proposed earlier from the Raman investigations. Beyond , 14 GPa, this compound undergoes another phase transformation to a significantly disordered structure. Both the phase transitions are found to be reversible. q

Determination of the high-pressure crystal structure ofBaWO4andPbWErrandonea1, Pellicer‐Porres2, Manjón3 et al. 2006Phys. Rev. B100191031View full textAdd to dashboardCite

“…Evidence of the occurrence of a second pressure-induced phase transition was previously observed by Panchal et al [16] albeit at the larger pressure of 14 GPa.…”

“…We think that the onset of this transition was previously overestimated in Ref. [16]. The occurrence of this kind of pressure-induced amorphization is sometimes related to a However, we have also observed some reversible changes on the features of the diffraction pattern at 15.6 GPa.…”

“…The existence of high-pressure (HP) high-temperature (HT) phases in BaWO 4 and PbWO 4 transforms to a high-pressure phase at 7 GPa and on the basis of the quality of the unitcell fit these authors suggested that the structure of this phase could be fergusonite and not HgWO 4 -type [16]. They also found evidence that beyond 14 GPa BaWO 4 undergoes another transition to an unidentified new phase.…”

First-order character of the displacive structural transition in BaWO 4

“…In any case, from the view of hydrostatic condition, there may be another scientific cause that a slight difference of hydrostatic circumstance would induce first or second-order competitive phase transitions in BaWO 4 . Nevertheless, on the basis of our own consistent diffraction and Raman experiments and the work of Jayaraman et al [11] and Panchal et al [9] using methanol-ethanol-water or methanol-ethanol mixture as a pressure medium, we support that the scheeliteto-fergusonite transition in BaWO 4 is of the first order. …”

“…Based on the continuous changes of lattice constants and volume with pressure, a second order 086201-7 nature of the phase transition is concluded. The authors also debated the difference between these results and Panchal et al's, [9] and considered that due to the restricted XRD measurement performed by Panchal et al, the lower resolution and the smaller access to the reciprocal space would lead to a larger uncertainty in the lattice parameters. Recently, Lacomba-Perales et al [15] pointed out that the different behaviours observed in different experiments could be related to the existence of pressure gradients in the particular experimental set up.…”