THERMAL-EXPANSION AND MOLAR VOLUME OF MGO, PERICLASE, FROM 5 TO 2900 K

Thermal expansion and molar volume of periclase are important paramete rs for thermodynamic modeling of the earth's interior. We have critica lly reviewed the available data and have found wide variations in the literature for MgO lattice parameters at room and high temperatures. E arlier Reeber (1975) developed an empirical quasi-harmonic model (QHM) that provides an excellent representation of thermal expansion from n ear 0 to 1200 K. Wang & Reeber (1995a) show for alkali halides that ab ove a temperature T-L,T- the approximate temperature where all lattice modes are effectively excited, experimentally measured thermal expans ion is slightly higher than an extrapolation of this empirical relatio nship. This difference is approximated with a 2nd order term that give s excellent quantitative agreement with experiment for alkali halides and cesium halides (Wang & Reeber, 1995b) to approximately 90% of the melting temperature. The existing literature for periclase is evaluate d within the constraints of the modified quasi-harmonic model (MQHM) a nd x-ray measurements at room temperature. At very high temperatures w here experimental data is not available the MQHM provides a method to estimate high temperature thermal expansion. Our best estimate of the lattice parameter at 0 K is 4.20565 Angstrom and at 298 K 4.21154 Angs trom.