科研之友
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摘要
We calculated the thermodynamic and thermoelastic properties of periclase and ferropericlase, the latter having a stoichiometric composition of (Fe0.03Mg0.97)O, at pressures and temperatures which are typical of the Earth%26apos;s lower mantle. The static lattice energies and vibrational frequencies were derived through ab initio calculations carried out at the hybrid HF/DFT level. The thermodynamic properties were calculated by following a standard statistical-thermodynamics approach, within the limit of the quasi-harmonic approximation. A third-order Birch-Murnaghan equation of state fit to the static E(V) data of periclase yielded K (0) = 163.8 GPa, K%26apos; = 4.3, and V (0) = 75.09 (3). The fit at 300 K and 0.1 MPa on the P(V) data yielded K (0) = 160.1 GPa, K%26apos; = 4.2, and V (0) = 75.99 (3). Such results successfully reproduced the best available experimental and previous computational data. The presence of iron with low-spin configuration in the structure had the effects (1) to reduce the cell volume, both at the static (74.19 (3)) and at the ambient conditions (75.14 (3)); (2) to increase the bulk modulus (respectively 172.2 GPa at the static limit, and 167.4 GPa at 298 K and 0.1 MPa), and (3) to decrease the thermal expansion (2.79 * 10(-5) K-1 for periclase and 2.60 * 10(-5) K-1 for ferropericlase at 300 K). Since the discussed parameters were also calculated at high pressure and temperature conditions simultaneously, the reliability of the quasi-harmonic approximation was tested by evaluating the shape of the potential energy curve, at conditions which simulate those of the Earth%26apos;s lower mantle. Such test confirmed the applicability of this approximation over all the P/T range considered.
- 出版日期2012-9
