Effect of pressure on La-2(WO4)(3) with a modulated scheelite-type structure

We have studied the effect of pressure on the structural and vibrational properties of lanthanum tritungstate La2(WO4)3. This compound crystallizes under ambient conditions in the modulated scheelite-type structure known as the α phase. We have performed x-ray diffraction and Raman scattering measurements up to a pressure of 20 GPa, as well as ab initio calculations within the framework of the density functional theory. Up to 5 GPa, the three methods provide a similar picture of the evolution under pressure of α-La2(WO4)3. At 5 GPa, we begin to observe some structural changes, and above 6 GPa we find that the x-ray patterns cannot be indexed as a single phase. However, we find that a mixture of two phases with C2/c symmetry accounts for all diffraction peaks. Our ab initio study confirms the existence of several C2/c structures, which are very close in energy in this compression range. According to our measurements, a state with medium-range order appears at pressures above 9 and 11 GPa, from x-ray diffraction and Raman experiments, respectively. Based upon our theoretical calculations we propose several high-pressure candidates with high cationic coordinations at these pressures. The compound evolves into a partially amorphous phase at pressures above 20 GPa.We acknowledge the financial support of the Spanish Ministerio de Economia y Competitividad under Grants MAT2010-21270-C04-02/03/04, CTQ2009-14596-C02-01, CSD2007-00045 and the Comunidad de Madrid and European Social Fund S2009/PPQ-1551-4161893. Access to the MALTA Cluster Computer (Universidad de Oviedo), the Atlante Super-computer (Instituto Tecnologico de Canarias, Red Espanola de Supercomputacion), and the MALTA Xcalibur Diffractometer (Universidad Complutense de Madrid) is gratefully acknowledged. C. G. A. wishes to thank the Agencia Canaria de Investigacion, Innovacion y Sociedad de la Informacion, and the European Social Fund of the Gobierno de Canarias for a fellowship. J.A.S. acknowledges financial support through the Juan de la Cierva fellowship program.Sabalisck, N.; Lopez Solano, J.; Guzmán-Afonso, C.; Santamaría Pérez, D.; González-Silgo, C.; Mújica, A.; Muñoz, A.... (2014). Effect of pressure on La-2(WO4)(3) with a modulated scheelite-type structure. Physical Review B (Condensed Matter). 89:1741121-17411211. https://doi.org/10.1103/PhysRevB.89.174112S17411211741121189Maczka, M., Souza Filho, A. G., Paraguassu, W., Freire, P. T. C., Mendes Filho, J., & Hanuza, J. (2012). Pressure-induced structural phase transitions and amorphization in selected molybdates and tungstates. Progress in Materials Science, 57(7), 1335-1381. doi:10.1016/j.pmatsci.2012.01.001Boulahya, K., Parras, M., & González-Calbet, J. M. (2005). A Structural Study of the Solid Solution Eu2(Mo1-xWx)3O12. 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Effect of pressure on La2(WO4)3 with a modulated scheelite-type structure

We have studied the effect of pressure on the structural and vibrational properties of lanthanum tritungstate La2(WO4)3. This compound crystallizes under ambient conditions in the modulated scheelite-type structure known as the α phase. We have performed x-ray diffraction and Raman scattering measurements up to a pressure of 20 GPa, as well as ab initio calculations within the framework of the density functional theory. Up to 5 GPa, the three methods provide a similar picture of the evolution under pressure of α-La2(WO4)3. At 5 GPa, we begin to observe some structural changes, and above 6 GPa we find that the x-ray patterns cannot be indexed as a single phase. However, we find that a mixture of two phases with C2/c symmetry accounts for all diffraction peaks. Our ab initio study confirms the existence of several C2/c structures, which are very close in energy in this compression range. According to our measurements, a state with medium-range order appears at pressures above 9 and 11 GPa, from x-ray diffraction and Raman experiments, respectively. Based upon our theoretical calculations we propose several high-pressure candidates with high cationic coordinations at these pressures. The compound evolves into a partially amorphous phase at pressures above 20 GPa