C. David Martin
Stony Brook University
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Featured researches published by C. David Martin.
American Mineralogist | 2006
C. David Martin; Wilson A. Crichton; Haozhe Liu; Vitali B. Prakapenka; Jiuhua Chen; John B. Parise
Abstract Neighborite (NaMgF3) with the perovskite structure, transforms to a post-perovskite (ppv) phase between 27 and 30 GPa. The ppv phase is observed to the highest pressures achieved (56 GPa) at room temperature and transforms to an as yet unknown phase upon heating. Rietveld structure refinement using monochromatic synchrotron X-ray diffraction data provide models for the perovskite and postperovskite structures at high pressure. The refined models at 27(1) GPa indicate some inter-octahedral F-F distances rival the average intra-octahedral distance, which may cause instability in the perovskite structure and drive the transformation to the post-perovskite phase. The ratio of A-site to B-site volume (VA/VB) in perovskite structured NaMgF3 (ABX3), spans from 5 in the zero-pressure high-temperature cubic perovskite phase to 4 in this high-pressure perovskite phase at 27(1) GPa, matching the VA/VB value in post-perovskite NaMgF3. Using Rietveld refinement on post-perovskite structure models, we observe discrepancies in pattern fitting, which may be described in terms of development of sample texture in the diamond-anvil cell, recrystallization, or a change of space group to Cmc21, a non-isomorphic subgroup of Cmcm-the space group describing the structure of CaIrO3.
American Mineralogist | 2007
C. David Martin; Karena W. Chapman; Peter J. Chupas; Vitali B. Prakapenka; Peter L. Lee; S. D. Shastri; John B. Parise
Abstract Analysis of pressure-temperature dependent monochromatic X-ray powder diffraction data yield the bulk modulus [KT = 180.2(28) GPa] and thermal expansion coeficients [α0 = 2.841(34) × 10-5 K-1; α1 = 3.37(48) × 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.
Applied Physics Letters | 2005
C. David Martin; Sytle M. Antao; Peter J. Chupas; Peter L. Lee; S. D. Shastri; John B. Parise
Using a diamond anvil cell with high-energy monochromatic x rays, we have studied the total scattering of nanocrystalline gold to 20A−1 at pressures up to 10GPa in a hydrostatic alcohol pressure-medium. Through direct Fourier transformation of the structure function [S(Q)], pair distribution functions (PDFs) [G(r)] are calculated without Kaplow-type iterative corrections. Quantitative high-pressure PDF (QHP-PDF) analysis is performed via full-profile least-squares modeling and confirmed through comparison of Rietveld analysis of Bragg diffraction. The quality of the high pressure PDFs obtained demonstrates the integrity of our technique and suggests the feasibility of future QHP-PDF studies of liquids, disordered solids, and materials at phase transition under pressure.
American Mineralogist | 2005
C. David Martin; Santanu Chaudhuri; Clare P. Grey; John B. Parise
Abstract We present a structural model for (K,Na)MgF3 perovskite using results from high-resolution synchrotron X-ray powder diffraction and nuclear magnetic resonance (NMR) spectroscopy. (K,Na)MgF3 perovskite is found to transition from orthorhombic (Pbnm) to tetragonal (P4/mbm) to cubic (Pm3̅m) as potassium concentration is increased. These phase transitions are not accompanied by a discontinuity in pseudo-cubic unit-cell volume and occur close to compositions (K0.37Na0.63)MgF3 and (K0.47Na0.53)MgF3, respectively. 19F NMR spectra indicate that the Na+ and K+ cations do not occupy the A cation site at random and end-member local environments are favored for all compositions. Based on results from both X-ray diffraction and NMR, we propose that diffuse diffraction is the result of strain between coexisting regions of different octahedra (MgF6) tilts brought about by the ionic radius mismatch of Na+ and K+ cations. We suggest A-site cations group with like cations as neighbors to reduce excess volume and total strain.
Powder Diffraction | 2007
Lars Ehm; Sytle M. Antao; Jiuhua Chen; Darren R. Locke; F. Marc Michel; C. David Martin; Tony Yu; John B. Parise; Peter L. Lee; Peter J. Chupas; S. D. Shastri; Quanzhong Guo
The method of high-energy total elastic X-ray scattering to determine the atomic structure of nanocrystalline, highly disordered, and amorphous materials is presented. The current state of the technique, its potential, and limitations are discussed with two successful studies on the pressure induced phase transition in mackinawite (FeS) and the high-pressure behavior of liquid gallium.
American Mineralogist | 2007
C. David Martin; Ronald I. Smith; William G. Marshall; John B. Parise
Abstract The structure of CaIrO3 (Cmcm) has been refined at high pressure and at low temperature using time-of-flight neutron powder diffraction data. Evidence supporting deviation from space group Cmcm to Cmc21 is inconclusive. As CaIrO3 (Cmcm) unit-cell volume changes, refinements indicate deformation of cation-centered coordination polyhedra, rather than tilting. Structure models demonstrate Ca2+-centered polyhedra are an order of magnitude more compressible than Ir4+-centered octahedra. Bond valence sums show significant chemical strain (over-bonding) of calcium and oxygen at ambient conditions. Implications for structure change in MgSiO3 post-perovskite are discussed and a method for predicting the Clapeyron slope between perovskite and post-perovskite phases is proposed based on extrapolation of the volume-ratio between cation-centered polyhedra.
American Mineralogist | 2005
Jiuhua Chen; Haozhe Liu; C. David Martin; John B. Parise; Donald J. Weidner
Abstract The crystal structure of NaMgF3 perovskite (neighborite) has been studied at 4 GPa and temperatures up to 1000 °C using the Rietveld structure-refinement method. In situ synchrotron X-ray powder diffraction data was collected using monochromatic radiation. The orthorhombic (Pbnm) to cubic (Pm3̅ m) transition was observed when the temperature increased from 900 to 1000 °C. Structure refinements show that the ratio of polyhedral volumes of the A and B sites (VA/VB) of the orthorhombic phase increases with temperature, approaching the ideal value (5) for the cubic structure. However, this ratio becomes smaller at 4 GPa compared to the result from previous studies at the same temperature but ambient pressure, indicating that pressure makes it more difficult to transform from the orthorhombic phase to the cubic phase in this kind of perovskite.
Geophysical Research Letters | 2006
C. David Martin; Wilson A. Crichton; Haozhe Liu; Vitali B. Prakapenka; Jiuhua Chen; John B. Parise
Geophysical Research Letters | 2007
Henry P. Scott; Sabrina Huggins; Mark R. Frank; Steven J. Maglio; C. David Martin; Javier D. Santillan; Quentin Williams
Earth and Planetary Science Letters | 2008
C. David Martin; John B. Parise