THERMOELASTIC PROPERTIES OF MGSIO3 PEROVSKITE DETERMINED BY IN-SITU X-RAY OBSERVATIONS UP TO 30 GPA AND 2000 K

In situ X ray experiments on MgSiO3 perovskite at pressures of 21 - 29 GPa and temperatures of 300 - 2000 K were carried out using an MA8-ty pe high-pressure apparatus, employing sintered diamond anvils, combine d with synchrotron radiation. The thermal expansion at 25 GPa up to 20 00 K was determined from interpolation of the P-V-T data obtained in t he present study. The 95% confidence level was estimated by taking all possible errors into account, including statistical error and systema tic error caused by uncertainty of pressure scales, etc. The thermal e xpansivity at 25 GPA is expressed as alpha(T,25) = a(25) + b(25)T - c( 25)T(2) with the bestfit parameters of a(25) = 2.11 x 10(-5) K-1, b(25 ) = 1.80x10(-9) K-2, and c(25) = 1.93 K. The equation of state of MgSi O3 perovskite has been determined using our new data combined with the lower-pressure data of Wang ed al. [1994] and Utsumi et al. [1995]. T he optimal set of parameters of the third-order Birch-Murnaghan equati on of state, which is expressed as P = (3/2)K-T,K-0[(V-T,V-0/V)(7/3) - (V-T,V-0/V)(5/3)]{1 - (3/4)(4 - K-T,K-0')[(V-T,V-0/V)(2/3) - 1]}, whe re K-T,K-0 = K300,0 +(partial derivative K-T,K-0/partial derivative T) (p)(T - 300), K-T,K-0 = K-300,K-0'' V-T,V-0 = V(0)exp integral(300)(T) alpha(T,0)dT, and alpha(T,0) = a(0) + b(0)T - c(0)T(-2), is K-300,K-0 = 261 GPa, K-300,K-0 = 4, a(0) = 1.982x10(-5) K-1, b(0) = 0.8L8x10(-8 ) K-2, c(0) = 0.474 K, and (partial derivative K-T,K-0/partial derivat ive T)(p) = -0.0280 GPa/K. The reliability of the result is discussed in detail.