Thermoelastic properties of periclase and magnesiowustite under high pressure and high temperature

A simple thermodynamic model for calculating the high-pressure and high-tem perature properties of MgO consistently is presented. The model explains ex perimental equation of state (EOS) to similar to 220 GPa at room temperatur e and shock-wave EOS to similar to 200 GPa very well. The calculated Hugoni ot temperature amounts to 3400 K at 200 GPa. The input parameters are the v olume of the unit cell, V-0,, bulk modulus, K-0, its pressure derivative, K '(0), Debye temperature, Theta(0), and a parameter relating to the shear mo dulus, f(44) all in the static lattice at zero pressure which are estimated from experimental data at room temperature and zero pressure. The calculat ed thermal expansivity, ct, and Anderson-Gruneisen parameters, delta(r) and delta(s) at zero pressure are in agreement with experimental data to 1000- 1250 K and those to 1800 K, respectively. Our model explains also experimen tal velocities upsilon(p) and upsilon(s) of compressional and shear waves t o 1800 K at zero pressure very well. The pressure-dependence of cu, u, and u, at room temperature agree reasonably with experimental data to 36 GPa at room temperature. Applying our model to magnesiowustite, we have calculate d the thermal EOS and shock-wave EOS in agreement with experimental data. T he implication of our result together with our previous one of magnesium-si licate perovskite for the composition of the lower mantle is briefly discus sed. (C) 1999 Elsevier Science B.V. All rights reserved.