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Dive into the research topics where C. David Martin is active.

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Featured researches published by C. David Martin.


American Mineralogist | 2006

Rietveld structure refinement of perovskite and post-perovskite phases of NaMgF3 (Neighborite) at high pressures

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

Compression, thermal expansion, structure, and instability of CaIrO3, the structure model of MgSiO3 post-perovskite

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

Quantitative high-pressure pair distribution function analysis of nanocrystalline gold

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

Effect of A-site cation radius on ordering of BX6 octahedra in (K,Na)MgF3 perovskite

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

Studies of Local and Intermediate Range Structure in Crystalline and Amorphous Materials at High Pressure Using High-Energy X-rays

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

High-pressure structure and bonding in CaIrO3: The structure model of MgSiO3 post-perovskite investigated with time-of-flight neutron powder diffraction

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

Crystal chemistry of NaMgF3 perovskite at high pressure and temperature

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

Phase transitions and compressibility of NaMgF3 (Neighborite) in perovskite- and post-perovskite-related structures

C. David Martin; Wilson A. Crichton; Haozhe Liu; Vitali B. Prakapenka; Jiuhua Chen; John B. Parise


Geophysical Research Letters | 2007

Equation of state and high-pressure stability of Fe3P-schreibersite: Implications for phosphorus storage in planetary cores

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

Structure constraints and instability leading to the post-perovskite phase transition of MgSiO3

C. David Martin; John B. Parise

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Jiuhua Chen

Florida International University

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Haozhe Liu

Argonne National Laboratory

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Peter J. Chupas

Argonne National Laboratory

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Peter L. Lee

Argonne National Laboratory

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S. D. Shastri

Argonne National Laboratory

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Wilson A. Crichton

European Synchrotron Radiation Facility

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