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Distortions and stabilization of simple-cubic calcium at high pressure and low temperature
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2010 (English)In: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 107, no 22, 9965-9968 p.Article in journal (Refereed) 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.

Place, publisher, year, edition, pages
2010. Vol. 107, no 22, 9965-9968 p.
Keyword [en]
high pressure, phase transition, superconductivity
National Category
Physical Sciences
URN: urn:nbn:se:uu:diva-136068DOI: 10.1073/pnas.1005279107ISI: 000278246000013OAI: oai:DiVA.org:uu-136068DiVA: diva2:376138
Available from: 2010-12-10 Created: 2010-12-09 Last updated: 2012-04-02Bibliographically approved

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Luo, WeiAhuja, Rajeev
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Department of Physics and Astronomy
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