HR: 1340h
AN: MR43C-1525    [Abstracts]
TI: Structure Investigation of CaSiO₃ Perovskite at 91 GPa
AU: * Martin, C
EM: c.dave.martin@gmail.com
AF: X-ray Science Division, Advanced Photon Source, Argonne National Laboratory 9700 S. Cass Avenue, Argonne, IL 60439, United States
AU: Prakapenka, V
EM: prakapenka@cars.uchicago.edu
AF: GeoSoil and EnviroCARS(GSECARS), Advanced Photon Source, Argonne National Laboratory 9700 S. Cass Avenue, Argonne, IL 60439, United States
AU: Parise, J B
EM: jparise@notes.cc.sunysb.edu
AF: Geosciences Department, 255 Earth and Space Sciences Building, Stony Brook University, Stony Brook, NY 11794-2100, United States
AB: The crystallographic structure of CaSiO₃ perovskite at 91(2) GPa is investigated using monochromatic X-ray diffraction and the laser-heated diamond anvil cell with a graphite gasket-insert to increase the volume of the sample under diffraction conditions. We report observations of weak X-ray reflections at d-spaces matching a perovskite super-structure, which appear in addition to splitting of diffraction from the cubic sub-structure. Considering this data in context with the space groups (SGs) of all perovskite structures observed experimentally and recorded in the Inorganic Crystal Structure Database, CaSiO₃ perovskite adopts one of two possible tetragonal structures ( P4/ mbm, SG #127, rather than I4/ mcm, SG #123) after cooling from 2000(300) K at this pressure if an orthorhombic or monoclinic unit cell is discounted. When an orthorhombic perovskite structure is considered, reflections from the perovskite super-structure discount Imam (SG #74) and could favor Cmcm (SG #74) above Pbnm (SG #62). The raw diffraction data from CaSiO₃ and our analysis are presented in addition to a detailed procedure for the construction of the graphite gasket-insert used during the high pressure experiment. In brief, graphite is machined from a monochromator by electronic discharge and placed within a conventional tungsten gasket. Oriented with its a-axis perpendicular to the direction of force in the diamond anvil cell, a sample chamber is machined within the graphite-insert after indenting with the diamond anvils.
DE: 3924 High-pressure behavior
DE: 3954 X-ray, neutron, and electron spectroscopy and diffraction
DE: 3994 Instruments and techniques
SC: Mineral and Rock Physics [MR]
MN: 2007 Fall Meeting