MICROSCOPIC ANHARMONICITY AND EQUATION OF STATE OF MGSIO3- PEROVSKITE

The effect of temperature on the Raman spectrum of MgSiO3-perovskite i s investigated between 77 and 300 K. The data, combined with those obt ained at high pressure, are used to infer microscopic anharmonic param eters (a(i)) It is shown that only two low-frequency Raman modes are s ignificantly anharmonic. The small volume dependency of the a(i) param eters allows a quasi-harmonic calculation of the thermal pressure from a simplified density of states of the vibrational modes without other a priori informations. The calculated high-temperature EOS reproduces to within +/- 0.4 % the experimental molar volume obtained in the 0.1 MPa-36 GPa and 77-2000 K range. A softening of a low-frequency mode w ith decreasing temperature is also observed.