Pressure-induced phase-transition sequence in CoF2: An experimental and first-principles study on the crystal, vibrational, and electronic properties
| Autor: | Barreda Argüeso, José Antonio, López-Moreno, S., Sanz Ortiz, Marta Norah, Aguado Menéndez, Fernando, Valiente Barroso, Rafael, González Gómez, Jesús Antonio, Rodríguez González, Fernando, Romero, A. H., Muñoz, A., Nataf, L., Baudelet, F. |
|---|---|
| Přispěvatelé: | Universidad de Cantabria |
| Rok vydání: | 2013 |
| Předmět: | |
| Zdroj: | Physical review. B, Condensed matter and materials physics, vol. 88, iss. 21, art. num. 214108 (2013) UCrea Repositorio Abierto de la Universidad de Cantabria Universidad de Cantabria (UC) Physical review. B, 2013, 88, 214108 Physical review B, 2013, 88, 214108 |
| ISSN: | 2010-2127 |
| Popis: | 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. Financial support from the Spanish Ministerio de Economia y Competitividad (Projects No. MAT2010-21270-C04-03 and No. MAT2012-38664-C02-1) and MALTA INGENIOCONSOLIDER 2010 (Ref. No. CDS2007-0045) and a Technical Grant (Ref. No. PTA2011-5461-I) is acknowledged. |
| Databáze: | OpenAIRE |
| Externí odkaz: |
|