Abstract

We studied MgSiO 3 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 alpha and compressibility beta against T (in K): alpha T = 2.71 X 10 (super -5) +1.80 X 10 9 T-1.48 T 2 (Model 1) or alpha T = 2.13 X 10 (super -5) +7.57 X 10 (super -9) T-1.02 T 2 (Model 2), and alpha T = 3.735 X 10 (super -7) +3.27 X 10 (super -11) T+6.60 X 10 (super -15) T 2 . 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: alpha = 1.1 X 10 (super -5) , K 0 (bulk modulus) = 261 GPA, K' 0 = 4 and (theta K/theta T) = -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 alpha 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, C p , data for perovskite is given by either: C p = 110.8+8.031 X 10 (super -3) T-1.302 X 10 (super -7) T 2 -1.647 X 10 7 T 2 +2.755 X 10 9 T (super -3) +267.5 T (super -0.5) +9287 T (super -1) (Model 1) or C p = 121.33+2.77 X 10 (super -3) T-2.585 X 10 (super -6) T 2 -1.710 X 10 7 T+2.792 X 10 9 T (super -3) -169 T (super -0.5) +15782 T (super -1) (Model 2).

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