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

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    URI: http://hdl.handle.net/10902/4391
    DOI: 10.1103/PhysRevB.88.214108
    ISSN: 1098-0121
    ISSN: 1550-235X
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    Author
    Barreda Argüeso, José AntonioAutoridad Unican; López Moreno, S.; Sanz Ortiz, Marta NorahAutoridad Unican; Aguado Menéndez, FernandoAutoridad Unican; Valiente Barroso, RafaelAutoridad Unican; González Gómez, Jesús AntonioAutoridad Unican; Rodríguez González, FernandoAutoridad Unican; Romero, Aldo H.; Muñoz González, Alfonso; Nataf, Lucie; Baudelet, Francois
    Date
    2013-12
    Derechos
    © 2013 American Physical Society
    Publicado en
    Physical review B, 2013, 88, 214108
    Publisher
    American Physical Society
    Enlace a la publicación
    http://dx.doi.org/10.1103/PhysRevB.88.214108
    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.
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    • D29 Artículos [194]
    • D29 Proyectos de Investigación [147]

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    UNIVERSIDAD DE CANTABRIA

    Repositorio realizado por la Biblioteca Universitaria utilizando DSpace software
    Contact Us | Send Feedback
    Metadatos sujetos a:licencia de Creative Commons Reconocimiento 3.0 España