Premium
Single‐crystal metastable high‐temperature C 2/ c clinoenstatite quenched rapidly from high temperature and high pressure
Author(s) -
Yoshiasa Akira,
Nakatsuka Akihiko,
Okube Maki,
Katsura Tomoo
Publication year - 2013
Publication title -
acta crystallographica section b
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.604
H-Index - 33
eISSN - 2052-5206
pISSN - 2052-5192
DOI - 10.1107/s2052519213028248
Subject(s) - metastability , quenching (fluorescence) , crystallography , crystal (programming language) , materials science , diffraction , degree (music) , single crystal , thermodynamics , chemistry , physics , optics , organic chemistry , computer science , acoustics , fluorescence , programming language
The high‐temperature clinoenstatite (HT‐CEn) is one of the most important MgSiO 3 pyroxene polymorphs, but the details of its structure and stability have been uncertain. The single crystal of the C 2/ c HT‐CEn end‐member is firstly synthesized by rapid pressure–temperature quenching from 15–16 GPa and 1173–2173 K. 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 C 2/ 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.