Complex high-pressure polymorphism of barium tungstate

O. Gomis (1) , J. A. Sans (2, 3) , R. Lacomba-Perales (2) , D. Errandonea (2) , Y. Meng (4) , J. C. Chervin (5) , A. Polian (5)

1 Departamento de Física Aplicada—ICMUV
2 Departamento de Fısica Aplicada-ICMUV
3 Instituto de Diseno para la Fabricacion y Produccion Automatizada, MALTA Consolider Team, Universitat Politecnica de Valencia
4 HPCAT, Carnegie Institution of Washington
5 IMPMC - Institut de minéralogie et de physique des milieux condensés

We have studied BaWO4 under compression at room temperature by means of x-ray diffraction and Raman spectroscopy. When compressed with neon as a pressure-transmitting medium (quasihydrostatic conditions), we found that BaWO4 transforms from its low-pressure tetragonal structure into a much denser monoclinic structure. This result confirms our previous theoretical prediction based on ab initio calculations that the scheelite to BaWO4-II transition occurs at room temperature if kinetic barriers are suppressed by pressure. However, our experiment without any pressure-transmitting medium has resulted in a phase transition to a completely different structure, suggesting nonhydrostaticity may be responsible for previously reported rich polymorphism in BaWO4. The crystal structure of the low- and high-pressure phases from the quasihydrostatic experiments has been Rietveld refined. Additionally, for the tetragonal phase the effects of pressure on the unit-cell volume and lattice parameters are discussed. Finally, the pressure evolution of the Raman modes of different phases is reported and compared with previous studies.

Domaines: Autre [cond-mat.other]

O. Gomis, J. A. Sans, R. Lacomba-Perales, D. Errandonea, Y. Meng, et al.. Complex high-pressure polymorphism of barium tungstate. Physical Review B: Condensed Matter and Materials Physics (1998-2015), 2012, 86, pp.054121. ⟨10.1103/PhysRevB.86.054121⟩. ⟨hal-00739950⟩