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Pressure-induced phase-transition sequence in CoF2: An experimental and first-principles study on the crystal, vibrational, and electronic properties

Abstract: We report a complete structural study of CoF2 under pressure. Its crystal structure and vibrational and electronic properties have been studied both theoretically and experimentally using first-principles density functional theory (DFT) methods, x-ray diffraction, x-ray absorption at Co K-edge experiments, Raman spectroscopy, and optical absorption in the 0?80 GPa range. We have determined the structural phase-transition sequence in CoF2 and corresponding transition pressures. The results are similar to other transition-metal difluorides such as FeF2 but different to ZnF2 and MgF2, despite that the Co2+ size (ionic radius) is similar to Zn2+ and Mg2+. We found that the complete phase-transition sequence is tetragonal rutile (P42/mnm)?CaCl2 type (orthorhombic Pnnm)?distorted PdF2 (orthorhombic Pbca) + PdF2 (cubic Pa3) in coexistence ¯ ? fluorite (cubic Fm3¯m) ? cotunnite (orthorhombic Pnma). It was observed that the structural phase transition to the fluorite at 15 GPa involves a drastic change of coordination from sixfold octahedral to eightfold cubic with important modifications in the vibrational and electronic properties. We show that the stabilization of this high-pressure cubic phase is possible under nonhydrostatic conditions since ideal hydrostaticity would stabilize the distorted-fluorite structure (tetragonal I4/mmm) instead. Although the first rutile ? CaCl2-type second-order phase transition is subtle by Raman spectroscopy, it was possible to define it through the broadening of the Eg Raman mode which is split in the CaCl2-type phase. First-principles DFT calculations are in fair agreement with the experimental Raman mode frequencies, thus providing an accurate description for all vibrational modes and elastic properties of CoF2 as a function of pressure.

Otras publicaciones de la misma revista o congreso con autores/as de la Universidad de Cantabria

 Autoría: Barreda-Argüeso J.A., López-Moreno S., Sanz-Ortiz M.N., Aguado F., Valiente R., González J., Rodríguez F., Romero A.H., Muñoz A., Nataf L., Baudelet F.,

 Fuente: Physical review. B, 2013, 88, 214108

Editorial: American Physical Society

 Año de publicación: 2013

Nº de páginas: 15

Tipo de publicación: Artículo de Revista

 DOI: 10.1103/PhysRevB.88.214108

ISSN: 1098-0121,1550-235X,2469-9950,2469-9969

Proyecto español: MAT2010-21270-C04-03

Url de la publicación: http://doi.org/10.1103/PhysRevB.88.214108

Autores/as

JOSE ANTONIO BARREDA ARGÜESO

LÓPEZ-MORENO, S.

MUÑOZ, A.

NATAF, L.

BAUDELET, F.