Quasi-harmonic computer simulations of the structural behaviour and EOS of pyrope at high pressure and high temperature |
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| Authors: | A Pavese |
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| Institution: | (1) Dipartimento di Scienze della Terra, Università di Milano, via Botticelli 23, I-20133 Milano, Italy e-mail: pavese@p8000.terra.unimi.it, IT |
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| Abstract: | Numerical simulations, using empirical interatomic potentials within the framework of lattice dynamics and quasi-harmonic
approximation, have been carried out to model the behaviour of the structure and of some thermoelastic properties of pyrope
at high pressure and high temperature conditions (0–50 GPa, 300–1500 K). Comparison with observed data, available as a function
either of P or of T, suggests that the pressure effects are satisfactorily modelled, whilst the effect of T on the simulations is underestimated. The cell edge, bond lengths and polyhedral volumes have been studied as a function
of P along five isotherms, spaced by 300 K steps. These isotherms tend to converge at high pressure, which demonstrates that the
pressure effects become dominant compared to those of thermal origin in affecting the structural properties far from ambient
conditions. The cell parameter, bond distances, and other structural and thermoelastic quantities determined through simulations
have been parametrised as a function of P and T by polynomial expansions. Bulk modulus and thermal expansion have been discussed in the light of the high-temperature-Birch-Murnaghan
and of the Vinet P – V – T equations of state. The predictions of the bulk modulus versus P and T from the present calculations and from the Vinet-EOS agree up to 10 GPa, but they differ at higher pressure.
Received: 23 October, 1998 / Revised, accepted: 23 April, 1999 |
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