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American Mineralogist; July 2007; v. 92; no. 7; p. 1048-1053; DOI: 10.2138/am.2007.2473
© 2007 Mineralogical Society of America
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Compression, thermal expansion, structure, and instability of CaIrO3, the structure model of MgSiO3 post-perovskite

C. David Martin1,*, Karena W. Chapman2, Peter J. Chupas2, Vitali Prakapenka3, Peter L. Lee2, Sarvjit D. Shastri2 and John B. Parise1,4

1 Geosciences Department, 255 Earth and Space Sciences Building, Stony Brook University, Stony Brook, New York 11794-2100, U.S.A.
2 X-ray Science Division, Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois 60439, U.S.A.
3 GeoSoil and EnviroCARS (GSECARS), Sector 13, Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois 60439, U.S.A.
4 Chemistry Department, Stony Brook University, Stony Brook, New York 11794-3400, U.S.A.

Correspondence: * E-mail: chmartin{at}ic.sunysb.edu

Analysis of pressure-temperature dependent monochromatic X-ray powder diffraction data yield the bulk modulus [KT = 180.2(28) GPa] and thermal expansion coefficients [{alpha}0 = 2.841(34) x 10–5 K–1; {alpha}1 = 3.37(48) x 10–9 K–2] of CaIrO3, the structure model for post-perovskite MgSiO3. CaIrO3 is orthorhombic (Cmcm, space group 63, Z = 4) with best-fit unit-cell parameters, a = 3.14147(5) Å, b = 9.87515(19), c = 7.29711(11), and V = 226.3754(78) Å3 at 1 bar and 300 K. The c-axis of CaIrO3 has a small compressibility and a large thermal expansion when compared to the other principal axes. Rietveld structure refinement reveals changes in CaIrO3 as a function of temperature in terms of IrO6 octahedra distortion. Dissociation of CaIrO3 at high temperature has possible implications for the post-perovskite MgSiO3 structure, Earth’s lower mantle, and D’’ layer.

Key Words: Post-perovskite • CaIrO3 • pressure • temperature • structure • X-rays • Rietveld refinement • D'' layer




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C. D. Martin, R. I. Smith, W. G. Marshall, and J. B. Parise
High-pressure structure and bonding in CaIrO3: The structure model of MgSiO3 post-perovskite investigated with time-of-flight neutron powder diffraction
American Mineralogist, November 1, 2007; 92(11-12): 1912 - 1918.
[Abstract] [Full Text] [PDF]


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