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Title: In-situ measurement of texture development rate in CaIrO 3 post-perovskite

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Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
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Journal Article: Published Article
Journal Name:
Physics of the Earth and Planetary Interiors
Additional Journal Information:
Journal Volume: 257; Journal Issue: C; Related Information: CHORUS Timestamp: 2017-07-03 09:11:17; Journal ID: ISSN 0031-9201
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Citation Formats

Hunt, Simon A., Walker, Andrew M., and Mariani, Elisabetta. In-situ measurement of texture development rate in CaIrO 3 post-perovskite. Netherlands: N. p., 2016. Web. doi:10.1016/j.pepi.2016.05.007.
Hunt, Simon A., Walker, Andrew M., & Mariani, Elisabetta. In-situ measurement of texture development rate in CaIrO 3 post-perovskite. Netherlands. doi:10.1016/j.pepi.2016.05.007.
Hunt, Simon A., Walker, Andrew M., and Mariani, Elisabetta. 2016. "In-situ measurement of texture development rate in CaIrO 3 post-perovskite". Netherlands. doi:10.1016/j.pepi.2016.05.007.
title = {In-situ measurement of texture development rate in CaIrO 3 post-perovskite},
author = {Hunt, Simon A. and Walker, Andrew M. and Mariani, Elisabetta},
abstractNote = {},
doi = {10.1016/j.pepi.2016.05.007},
journal = {Physics of the Earth and Planetary Interiors},
number = C,
volume = 257,
place = {Netherlands},
year = 2016,
month = 8

Journal Article:
Free Publicly Available Full Text
Publisher's Version of Record at 10.1016/j.pepi.2016.05.007

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  • The rate of crystallographic preferred orientation (CPO) development during deformation of post-perovskite is crucial in interpreting seismic anisotropy in the lowermost mantle but the stability field of MgSiO 3 post-perovskite prevents high-strain deformation experiments being performed on it. Therefore, to constrain the rate of CPO development in post-perovskite, we deformed CaIrO 3, a low-pressure analogue of MgSiO 3 post-perovskite, in simple shear at 3.2 GPa and 400 °C to a shear strain (γ) of 0.81. From X-ray diffraction patterns acquired during deformation, we invert for CPO as a function of strain. By comparing the CPO that develops with visco-plastic self-consistentmore » (VPSC) models we constrain the critical resolved shear stresses (CRSS) of the non-primary slip-systems in CaIrO 3 to be of order 6 times stronger than the primary [100] (010) slip system. This value is significantly less than has been assumed by previous studies and if applicable to MgSiO 3 implies that seismic anisotropy in the D" layer develops slower than has previously been assumed.« less
  • At near ambient conditions, CaIrO{sub 3} is isostructural with the high-pressure polymorph MgSiO{sub 3} 'post-perovskite' (pPv). MgSiO{sub 3} pPv is thought to be a major phase in the earth's lowermost mantle. CaIrO{sub 3} can thus serve as an analog for studying deformation of the pPv phase under conditions achievable with a multi-anvil deformation apparatus. Here we study the rheologic behavior of CaIrO{sub 3} pPv at a variety of pressure and temperature conditions from 2 GPa to 6 GPa and 300 K to 1300 K and various strain rates. Sintered, polycrystalline CaIrO{sub 3} pPv, cylindrical in shape, was deformed in themore » D-DIA multi-anvil press in several shortening cycles up to 20% axial strain at each temperature and pressure. Shortening cycles were followed by lengthening back to 0% strain. Quantitative texture information was obtained using in-situ synchrotron X-ray diffraction and the Rietveld method to analyze images. In all cases we find that (010) lattice planes align perpendicular to the compression direction upon shortening, and that there is little change in texture with temperature or pressure. This texture pattern is consistent with slip on (010)[100]. The texture observed here is different from that produced in room temperature diamond anvil cell (DAC) experiments on MgGeO{sub 3} and MgSiO{sub 3} pPv which both display textures of (100) and {l_brace}110{r_brace} lattice planes at high angles to the compression direction. This implies that CaIrO{sub 3} pPv may not be a good analog for the plastic behavior of MgSiO{sub 3} pPv.« less
  • The electronic spin and valence states of Fe in post-perovskite ((Mg{sub 0.75}Fe{sub 0.25})SiO{sub 3}) have been investigated by synchrotron X-ray diffraction, Moessbauer and X-ray emission spectroscopy at 142 GPa and 300 K. Rietveld refinement of the X-ray diffraction patterns revealed that our sample was dominated by CaIrO{sub 3}-type post-perovskite. Combined Moessbauer and X-ray emission results show that Fe in post-perovskite is predominantly Fe{sup 2+} (70%) in the intermediate-spin state with extremely high quadrupole splitting of 3.77(25) mm/s. The remaining 30% Fe can be assigned to two sites. Compared with recent studies, our results indicate that the intermediate-spin Fe{sup 2+} ismore » stabilized in CaIrO{sub 3}-type post-perovskite over a wide range of Fe content, whereas the low-spin Fe{sup 3+} is more dominant in the 2 x 1 kinked post-perovskite structure. The characterization of these structural and compositional effects on the spin and valence states of Fe in post-perovskite can help in understanding the geochemical and geophysical behavior of the core-mantle region.« less
  • The dynamics of texture formation, changes in crystal structure and stress accommodation mechanisms are studied in R3c rhombohedral LaCoO3 perovskite during in-situ uniaxial compression experiment by neutron diffraction. The neutron diffraction revealed the complex crystallographic changes causing the texture formation and significant straining along certain crystallographic directions during in-situ compression, which are responsible for the appearance of hysteresis and non-linear ferroelastic deformation in LaCoO3 perovskite. The irreversible strain after the first loading was connected with the appearance of non-recoverable changes in the intensity ratio of certain crystallographic peaks, causing non-reversible texture formation. However in the second loading/unloading cycle the hysteresismore » loop was closed and no irreversible strain appears after deformation. The significant texture formation is responsible for increase in the Young s modulus of LaCoO3 at high compressive loads, where the reported values of Young s modulus increase from 76 GPa measured at the very beginning of the loading to 194 GPa at 900 MPa applied compressive stress measured at the beginning of the unloading curve.« less