First-principles calculations of the stability of hydrous alumino-silicates under deep-Earth conditions
stability of crystal structures
Gibbs free energy
degrees of freedom
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Publisher:The Ohio State University
Series/Report no.:The Ohio State University. School of Earth Sciences Senior Theses; 2010
The percent disorder affects many properties which control mineral behavior. This study used density functional theory to calculate the disorder and its effects on the energy of formation, the bulk modulus and its pressure derivative, and the minimization of the Gibbs free energy. The fully ordered structures of Phase Egg and Topaz-OH have Zero-pressure volumes (Vo = 205.4 Ǻ3 and Vo = 346.8 Ǻ3 respectively) are within 3.5% and 0.5% of reported values. Both the bulk modulus and Zero-pressure follow a linear trend with respect to the percent disorder. The Gibbs free energy for Phase Egg has a minimum at 50% disorder and Topaz-OH shows and even higher favoring of disorder at 60%. At higher pressure regimes the formation of phase Egg is energetically favorable compared to the formation of topaz-OH and stishovite.
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