Ab Initio Study of Structure and Compressibility of Garnets
The structure and properties of anhydrous end-members of the garnet family (ugrandite and pyralspite garnets) have been investigated as a function of applied pressure. We also calculated properties of hydrogrossular and hydropyrope at ambient and high pressure and explained the experimentally observed difference in the stability of the hydrogarnet substitution in grossular and pyrope. The study has been performed with the density-functional theory code CASTEP that uses pseudopotentials and plane-wave basis set.
The geometrical parameters of the unit cells containing in excess of 80 atoms have been fully optimised. The calculated static geometry, bulk modulus and its pressure derivative are in good agreement with the available experimental data. It is shown that the framework distortion achieved through the bending of the angle between the octahedra and tetrahedra is the main compression mechanism for all garnets studied.
KeywordsBulk Modulus Pressure Derivative Garnet Structure Si04 Tetrahedron Neutron Powder Diffraction Study
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