Modeling the Thermodynamic Parameters of Orthorhombic Perovskites from Vibrational Data
Abstract
Detailed knowledge of thermodynamic parameters allow consistency checks of phase equilibrium data and evaluation of Earth models once the properties of candidate minerals are known. Orthorhombic perovskites are a major lower mantle constituent whose properties are well studied and still controversial. While end member properties have been most studied, the effects of the addition of other elements such as iron and aluminum are less known. We have undertaken the study of several orthorhombic perovskites in order to develop a sensible thermodynamic model. Heat capacities, entropies, thermal pressure and thermal expansion may be calculated using vibrational data at ambient and high pressures. Heat capacities and entropies of six orthorhombic (Pbca) perovskites (CaGeO3, SrCeO3, BaCeO3, SrZrO3, CaZrO3, and YAlO3) were calculated using densities of states modeled after MgSiO3 perovskite from our previous work but modified based Raman and infrared data. We obtained excellent agreement between the available calorimetric and vibrational modeling heat capacities, which allows a general form for orthorhombic perovskites roughly based on unit cell volume. None of the perovskites in this study contain atoms with d or f electrons, so electronic properties were not considered. Results for thermal expansivity and thermal pressures for calcium germanate, yttrium aluminate and strontium zirconate perovskites from high pressure spectroscopic data will also be presented.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2006
- Bibcode:
- 2006AGUFMMR34A..02C
- Keywords:
-
- 3611 Thermodynamics (0766;
- 1011;
- 8411);
- 3924 High-pressure behavior;
- 3934 Optical;
- infrared;
- and Raman spectroscopy;
- 3939 Physical thermodynamics;
- 3949 Thermal expansivity