Single-crystal metastable high-temperature C2/c clinoenstatite quenched rapidly from high temperature and high pressure.
Single-crystal metastable high-temperature C2/c clinoenstatite quenched rapidly from high temperature and high pressure.
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DOI：
10.1107/s2052519213028248
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发表时间：
2013-12
期刊：
影响因子：
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通讯作者：
A. Yoshiasa;A. Nakatsuka;M. Okube;T. Katsura
中科院分区：
文献类型：
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作者：
A. Yoshiasa;A. Nakatsuka;M. Okube;T. Katsura
高温斜顽火辉石（HT-CEn）是最重要的MgSiO 3辉石多晶型物之一，但其结构和稳定性的细节一直不确定。在15-16 GPa和1173-2173 K的压力下，采用压温急冷法首次合成了C2/cHT-CEn端元单晶。单晶X射线衍射分析表明，不寻常的键距和静态无序的原子冻结在这个亚稳结构。对于HT-CEn，硅酸盐四面体链的扭结度为175°。HP-CEn的链角基本上较小（135°），但L-CEn的角在相反方向上为-160°（= 200°）。对于从HT-CEn到L-CEn的过渡，扭结程度通过弯曲超过180°而增加。对于从膨胀到拉伸的反向变化，在连续点处存在一个势垒。结果表明：HT-CEn单晶是由高压C2/c斜顽辉石（HP-CEn）经等对称相变形成的。天然岩石中HP-CEn中HT-CEn的存在是淬火历史的指示，这导致它存在于冲击陨石和撞击材料中的可能性。
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 1173-2173 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 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.