Equation of state of MgSiO3 with the perovskite structure based on experimental measurement

• Published in: The American mineralogist 1999-03, Vol.84 (3), p.226-232
• Main Authors: Saxena, Surendra K, Dubrovinsky, Leonid S, Tutti, Faramarz, Le Bihan, Tristan
• Format: Article
• Language: English
• Subjects: Geophysics; high pressure; high temperature; mantle; Mineralogy; Minerals; Optics; perovskite structure; phase transitions; physical properties; pressure; related to mantle; temperature; thermodynamic properties; Thermodynamics; X-ray diffraction; X-rays
• ISSN: 0003-004X; 1945-3027
• DOI: 10.2138/am-1999-0303

We studied MgSiO3 with the perovskite structure heated to temperatures up to 1500 K at pressures between 36 and 110 GPa with in-situ X-ray diffraction. The new pressure-volume-temperature (P-V-T) data were combined with literature data to provide thermal expansivity α and compressibility β against T (in K): αT = 2.71 × 10-5+1.80 × 109 T-1.48 T2 (Model 1) or αT = 2.13 × 10-5+7.57 × 10-9 T-1.02 T2 (Model 2), and αT = 3.735 × 10-7+3.27 × 10-11 T+6.60 × 10-15 T2. Model 1 yields physical properties of perovskite that confirm Anderson's (1998) Debye approach; the model is valid for extrapolation to 3000 K or more. The parameters at 300 K are: α = 1.1 × 10-5, K0 (bulk modulus) = 261 GPA, K'0 = 4 and (θK/θT) = -0.027. Thermal expansivity from this model does not fit the data of Funamori et al. (1996) at high temperature for P = 25 GPa. Model 2 uses an equation for α based on the data of Funamori et al. (1996), fits the available experimental data closely, and maintains conformity with Anderson's Debye approach. Heat capacity, Cp, data for perovskite is given by either: Cp = 110.8+8.031 × 10-3 T-1.302 × 10-7 T2-1.647 × 107 T2+2.755 × 109 T-3+267.5 T-0.5+9287 T-1 (Model 1) or Cp = 121.33+2.77 × 10-3 T-2.585 × 10-6 T2-1.710 × 107 T+2.792 × 109 T-3-169 T-0.5+15782 T-1 (Model 2).