Polymorphism in Strontium Tungstate SrWO4under Quasi-Hydrostatic Compression.
The structural and vibrational properties of SrWO4have been studied experimentally up to 27 and 46 GPa, respectively, by angle-dispersive synchrotron X-ray diffraction and Raman spectroscopy measurements as well as using ab initio calculations. The existence of four polymorphs upon quasi-hydrostatic compression is reported. The three phase transitions were found at 11.5, 19.0, and 39.5 GPa. The ambient-pressure SrWO4tetragonal scheelite-type structure (S.G. I41/a) undergoes a transition to a monoclinic fergusonite-type structure (S.G. I2/a) at 11.5 GPa with a 1.5% volume decrease. Subsequently, at 19.0 GPa, another structural transformation takes place. Our calculations indicate two possible post-fergusonite phases, one monoclinic and the other orthorhombic. In the diffraction experiments, we observed the theoretically predicted monoclinic LaTaO4-type phase coexisting with the fergusonite-type phase up to 27 GPa. The coexistence of the two phases and the large volume collapse at the transition confirm a kinetic hindrance typical of first-order phase transitions. Significant changes in Raman spectra suggest a third pressure-induced transition at 39.5 GPa. The conclusions extracted from the experiments are complemented and supported by ab initio calculations. Our data provides insight into the structural mechanism of the first transition, with the formation of two additional W-O contacts. The fergusonite-type phase can be therefore considered as a structural bridge between the scheelite structure, composed of [WO4] tetrahedra, and the new higher pressure phases, which contain [WO6] octahedra. All the observed phases are compatible with the high-pressure structural systematics predicted for ABO4compounds using crystal-chemistry arguments such as the diagram proposed by Bastide.
Departamento de Física Aplicada-ICMUV, Universidad de Valencia , MALTA Consolider Team, Edificio de Investigación, C/Dr. Moliner 50, E-46100 Burjassot, Valencia, Spain.
David
D
Santamaria-Perez
Departamento de Física Aplicada-ICMUV, Universidad de Valencia , MALTA Consolider Team, Edificio de Investigación, C/Dr. Moliner 50, E-46100 Burjassot, Valencia, Spain.
Daniel
D
Errandonea
Departamento de Física, Instituto de Materiales y Nanotecnología, Universidad de La Laguna , MALTA Consolider Team, E-38206 La Laguna, Tenerife, Spain.
Placida
P
Rodriguez-Hernandez
Departamento de Física, Instituto de Materiales y Nanotecnología, Universidad de La Laguna , MALTA Consolider Team, E-38206 La Laguna, Tenerife, Spain.
Alfonso
A
Muñoz
Departamento de Física Aplicada-ICMUV, Universidad de Valencia , MALTA Consolider Team, Edificio de Investigación, C/Dr. Moliner 50, E-46100 Burjassot, Valencia, Spain.
Raul
R
Lacomba-Perales
IMPMC, Institut de Minéralogie, de Physique des Matériaux et de Cosmochimie, Sorbonne Universités , UMPC Université Paris 06, UMR CNRS 7590, F-75005 Paris, France.
Alain
A
Polian
HPCAT, Carnegie Institution of Washington , APS Bldg 434E, 9700 South Cass Avenue, Argonne IL60439, United States.
Yue
Y
Meng