Molecular dynamics simulations of the phase transition between low-temperature and high-temperature clinoenstatites |
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| Authors: | N Shimobayashi A Miyake M Kitamura E Miura |
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| Institution: | Department of Geology and Mineralogy, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan?E-mail: shimo@kueps.kyoto-u.ac.ip?Tel.: +81-75-753-4156?Fax: +81-75-753-4189, JP
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| Abstract: | Phase transition between low-temperature clinoenstatite (LT-CEn) and high-temperature clinoenstatite (HT-CEn) was studied
by using molecular dynamics (MD) simulations, based on empirical potential parameters. Starting from LT-CEn, the MD calculations
were carried out at atmospheric pressure and at elevated pressures (1–6 GPa). At elevated temperatures the transformation
from the starting LT-CEn to HT-CEn occurred at any pressure. It was confirmed that the HT-CEn has the same space group C2/c as diopside but the M2 site is six-coordinated, unlike diopside. A significant difference in the MD-simulated cell volumes
between LT-CEn and HT-CEn was also observed, showing a first-order transition. In addition, there were some temperature ranges
where LT-CEN and HT-CEn would be coexistent and very small thermal hystereses between increasing and decreasing temperatures
during the transition. These behaviors are consistent with the characteristic of a thermoelastic-martensitic transformation.
The phase boundary between LT-CEn and HT-CEn was determined for the first time. Its positive dT/dP slope strongly shows that the high-pressure clinoenstatite is a significantly distinct phase from HT-CEn although the both
phases have the same space group, C2/c.
Received: 8 November 2000 / Accepted: 28 April 2001 |
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| Keywords: | Molecular dynamics simulation Clinoenstatite Polymorph Phase transformation |
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