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Distortions and stabilization of simple-cubic calcium at high pressure and low temperature
Vise andre og tillknytning
2010 (engelsk)Inngår i: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 107, nr 22, s. 9965-9968Artikkel i tidsskrift (Fagfellevurdert) Published
Abstract [en]

Ca-III, the first superconducting calcium phase under pressure, was identified as simple-cubic (sc) by previous X-ray diffraction (XRD) experiments. In contrast, all previous theoretical calculations showed that sc had a higher enthalpy than many proposed structures and had an imaginary (unstable) phonon branch. By using our newly developed submicrometer high-pressure single-crystal XRD, cryogenic high-pressure XRD, and theoretical calculations, we demonstrate that Ca-III is neither exactly sc nor any of the lower-enthalpy phases, but sustains the sc-like, primitive unit by a rhombohedral distortion at 300 K and a monoclinic distortion below 30 K. This surprising discovery reveals a scenario that the high-pressure structure of calcium does not go to the zero-temperature global enthalpy minimum but is dictated by high-temperature anharmonicity and low-temperature metastability fine-tuned with phonon stability at the local minimum.

sted, utgiver, år, opplag, sider
2010. Vol. 107, nr 22, s. 9965-9968
Emneord [en]
lattice-dynamics, phase, ca, vanadium, metals, sodium
HSV kategori
Identifikatorer
URN: urn:nbn:se:kth:diva-24635DOI: 10.1073/pnas.1005279107ISI: 000278246000013PubMedID: 20479266Scopus ID: 2-s2.0-77953466588OAI: oai:DiVA.org:kth-24635DiVA, id: diva2:352247
Merknad
QC 20100920Tilgjengelig fra: 2010-09-20 Laget: 2010-09-20 Sist oppdatert: 2024-03-18bibliografisk kontrollert
Inngår i avhandling
1. Theoretical Investigations of Compressed Materials
Åpne denne publikasjonen i ny fane eller vindu >>Theoretical Investigations of Compressed Materials
2010 (engelsk)Doktoravhandling, med artikler (Annet vitenskapelig)
Abstract [en]

The use of high pressure as a tool to design new materials as well as to investigatematerials properties has become increasingly important during last one decade. The maingoal of the present thesis is to enhance the significance of the high pressure method as aquantitative tool in solid state investigations. Virtually all of the properties of solids aredirectly determined by their electronic structure. Similarly, the changes in the propertiesof solids under pressure are determined by the changes in the electronic structure underpressure. We have attempted to provide a comprehensive description of the resulting theoryin a electronic structure and the properties of condensed matter.

The theoretical basis for these investigations is the density functional theory, in combinationwith ab initio method. The study of pressure induced phase transitions for thecompounds of CaF2, Cr2GeC, Ti3SiC2, as well as V at 0 K are presented. The latticeparameters, the phase transition pressures, the equation of states, the electronic structureshave been calculated and shown a good agreement with experimental results.

A lattices dynamic study of the body center cubic (bcc) Fe under high pressure andhigh temperature is presented. The bcc iron could dynamical stabilize in the Earth innercore conditions. The unusual phase transition of bcc V under high pressure is investigatedand it is shown that the driving mechanism is electron-phonon interaction.

Finally, a method based on the LDA+U approach has been applied to study spin statetransition in FeCO3. Our results show that magnetic entropy play a significant role in spinstate transition.

sted, utgiver, år, opplag, sider
Stockholm: KTH, 2010. s. 34
HSV kategori
Identifikatorer
urn:nbn:se:kth:diva-24641 (URN)9789174157352 (ISBN)
Disputas
2010-10-08, Sal D3, Lindstedtsvägen 5, KTH, Stockholm, 10:00
Opponent
Veileder
Merknad
QC 20100920Tilgjengelig fra: 2010-09-20 Laget: 2010-09-20 Sist oppdatert: 2022-06-25bibliografisk kontrollert

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