Crystal structure, compressibility and possible phase transitions in e-FeSi studied by ®rstprinciples pseudopotential calculations

Lidunka VocÏadlo, Geoffrey D. Price and I. G. Wood*

 Research School of Geological and Geophysical Sciences, University College London, Gower Street, London WC1E 6BT, England.

E-mail: wood@crystal.geol.ucl.ac.uk

(Received 4 September 1998; accepted 22 January 1999 )


Abstract:

An investigation of the relative stability of the FeSi structure and of some hypothetical polymorphs of FeSi has been made by ®rst-principles pseudopotential calculations. It has been shown that the observed distortion from ideal sevenfold coordination is essential in stabilizing the FeSi structure relative to one of the CsCl type. Application of high pressure to FeSi is predicted to produce a structure having nearly perfect sevenfold coordination. However, it appears that FeSi having a CsCl-type structure will be the thermodynamically most stable phase for pressures greater than 13 GPa. Fitting of the calculated internal energy vs volume for the FeSi structure to a third-order Birch± Murnaghan equation of state led to values, at T = 0 K, for the bulk modulus, K0, and for its ®rst derivative with respect to pressure, K0 0 , of 227 GPa and 3.9, respectively.


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