Distortions and stabilization of simple-cubic calcium at high pressure and low temperature
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
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.
lattice-dynamics, phase, ca, vanadium, metals, sodium
Engineering and Technology
IdentifiersURN: urn:nbn:se:kth:diva-24635DOI: 10.1073/pnas.1005279107ISI: 000278246000013ScopusID: 2-s2.0-77953466588OAI: oai:DiVA.org:kth-24635DiVA: diva2:352247
QC 201009202010-09-202010-09-202010-09-20Bibliographically approved