Single-crystal metastable high-temperature C2/c clinoenstatite quenched rapidly from high temperature and high pressure

Akira Yoshiasa, Akihiko Nakatsuka, Maki Okube, Tomoo Katsura

Research output: Contribution to journalArticlepeer-review

3 Citations (Scopus)

Abstract

The high-temperature clinoenstatite (HT-CEn) is one of the most important MgSiO3 pyroxene polymorphs, but the details of its structure and stability have been uncertain. The single crystal of the C2/c HT-CEn end-member is firstly synthesized by rapid pressure-temperature quenching from 15-16 GPa and 1173-2173K. The single-crystal X-ray diffraction analysis shows unusual bonding distances and static disorder of the atoms frozen in this metastable structure. The degree of kinking of the silicate tetrahedral chains is 175° for HT-CEn. The chain angle for HP-CEn is substantially smaller (135°), but the angle for L-CEn is in the opposite direction at -160° (= 200°). The degree of kinking increases by being curved by more than 180° for the transition from HT-CEn to L-CEn. As for the reverse change from the expansion to the stretch, a potential barrier exists at the point of the continuity. It is suggested that the reason why a structure can be quenched under ambient conditions is as follows: the present HT-CEn single crystal has been formed by the isosymmetric phase transition from the high-pressure C2/c clinoenstatite (HP-CEn). The presence of HT-CEn from HP-CEn in natural rocks is an indicator of quenching history, which leads to the possibility that it exists in shocked meteorites and impact materials.

Original languageEnglish
Pages (from-to)541-546
Number of pages6
JournalActa Crystallographica Section B: Structural Science, Crystal Engineering and Materials
Volume69
Issue number6
DOIs
Publication statusPublished - 2013 Dec 1

Keywords

  • clinoenstatite
  • phase transitions
  • polymorphism
  • pressure-temperature quenching

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Atomic and Molecular Physics, and Optics
  • Metals and Alloys
  • Materials Chemistry

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