Crystal Structural Analysis of New Phases Formed Under Mantle Conditions in Geological Systems

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LeinenweberEAR-0074089High pressure silicate and titanate crystals are being grown using a multianvil apparatus at pressures from 5 GPa to over 20 GPa, and the structures solved using single-crystal x-ray diffraction, in order to understand more about how the atomic structures of rock-forming minerals change during high pressure phase transitions in the Earth's mantle. The targets in this study include magnesium- and calcium-bearing silicates and titanates with H2O and/or fluorine, and so the basic idea is to extend the understanding of minerals under pressure to include more diverse compositions than are currently understood. The study takes advantage of the multianvil facility at Arizona State University for high pressure synthesis, along with a new single-crystal x-ray diffractometer installed in the Chemistry Department. New methods of crystal growth, in particular the growth of large crystals using unusual high pressure liquids such as molten Ca(OH)2 as a growth medium, are being used to produce the samples. Also, in some cases the samples must be recovered in liquid nitrogen (-196 degrees Centigrade), because they will not survive decompression at room temperature. Materials such as CaSiO3 perovskite behave this way, and this material in particular will be targeted for this type of treatment. The crystals will be transferred over to the diffractometer cold, and the diffractometer has a liquid nitrogen attachment so the sample stays cold while it is studied. The knowledge of the existence of these high pressure silicates and their atomic structures will be used to help understand what happens to elements in the Earth's mantle; what kind of structures they can occur in, and how they might be transported during dynamic processes.