Journal ArticleDOI
Cation ordering and structural variations with temperature in MgAl2O4 spinel: An X-ray single-crystal study
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TLDR
In this paper, the equilibrium distribution of Mg and Al between the tetrahedral and octahedral sites of a flux grown, stoichiometric MgAl2O4 spinel was investigated between 600 and 1100 °C by single-crystal X-ray diffraction of quenched samples.Abstract:
The equilibrium distribution of Mg and Al between the tetrahedral and octahedral sites of a flux grown, stoichiometric MgAl2O4 spinel was investigated between 600 and 1100 °C by single-crystal X-ray diffraction of quenched samples. The cation distribution for both ordering and disordering runs was obtained by minimizing accurate crystallographic parameters and effective ionic radii. Along with the variation of the degree of inversion from 0.18 to 0.29 between 600 and 1100 °C, both unit cell and oxygen positional parameter decreased linearly. Multiple non-linear least-squares fit of our data with the thermodynamic model of O’Neill and Navrotsky (1983) gave α = 23 ± 2 KJ/mol and β = 13 ± 4 KJ/mol. The influence of both cation inversion and thermal expansion on T-O and M-O bond length variation was determined by comparison of our data with previous in situ studies. In the thermal interval investigated, the inversion accounts for change of −0.014 A for T-O and +0.007 A for M-O. Mean linear polyhedral thermal expansion coefficients of 6.5 × 10−6 °C−1 and 8.9 × 10−6 °C−1 were calculated for T and M sites, respectively.read more
Citations
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Fifty Years of Research and Development Coming to Fruition; Unraveling the Complex Interactions during Processing of Transparent Magnesium Aluminate (MgAl2O4) Spinel
TL;DR: In this paper, the state-of-the-art in transparent polycrystalline spinel fabrication is presented, and the interaction between these key variables during processing is discussed.
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Raman spectroscopy of minerals and mineral pigments in archaeometry
TL;DR: A detailed knowledge of the mineral phases is crucial to solve archaeological problems: Raman spectroscopy is a powerful investigation technique and has been applied extensively in the last 30 years on mineral identification and on pigment degradation as mentioned in this paper.
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Critical thermodynamic evaluation and optimization of the MgO-Al2O3, CaO-MgO-Al2O3, and MgO-Al2O3-SiO2 Systems
TL;DR: In this article, a complete literature review, critical evaluation, and thermodynamic modeling of the phase diagrams and phase properties of all oxide phases in the MgO-Al2O3, CaO-MgOAl 2O3-SiO2 systems at 1 bar total pressure is presented.
Journal ArticleDOI
Melting of Peridotites through to Granites: A Simple Thermodynamic Model in the System KNCFMASHTOCr
TL;DR: In this article, a new set of thermodynamic models for calculating phase relations in bulk compositions extending from peridotite to granite, from 0·001 to 70 kbar and from 650°C to peridotsite liquidus temperatures, in the system K2O-Na2O-,CaO-FeO-MgO-Al2O3-SiO2-H2O,TiO2 -Fe2O)-Fe2-Fe3-Cr2O 3 (KNCFMASHTOCr).
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Prediction of ground-state structures and order-disorder phase transitions in II-III spinel oxides: A combined cluster-expansion method and first-principles study
TL;DR: In this paper, the ground states of six I-III spinel oxides were predicted by combining the cluster expansion method and first principles calculations, and their transition temperatures were evaluated using Monte Carlo simulations.
References
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Journal ArticleDOI
Revised effective ionic radii and systematic studies of interatomic distances in halides and chalcogenides
TL;DR: The effective ionic radii of Shannon & Prewitt [Acta Cryst. (1969), B25, 925-945] are revised to include more unusual oxidation states and coordinations as mentioned in this paper.
Journal Article
Simple spinels; crystallographic parameters, cation radii, lattice energies, and cation distribution
TL;DR: In this article, a set of cation radii optimized to best fit spinel lattice parameters is presented, where the size of a cation is important in determining its site preference.
Journal Article
Cation distributions and thermodynamic properties of binary spinel solid solutions.
TL;DR: In this article, a general model is presented to enable the calculation of the cation distribution and thermodynamic properties of any binary solid solution between oxide spinels containing 2+,3+ and 4+ cations, including the effect of disordering enthalpy which depends linearly on the degree of disorder.
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An internally consistent model for the thermodynamic properties of Fe−Mg-titanomagnetite-aluminate spinels
Richard O. Sack,Mark S. Ghiorso +1 more
TL;DR: In this article, a model for the thermodynamic properties of Fe2+−Mg2+-aluminate-titanate-ferrite spinels of space group Fd3m was developed.
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Thermodynamics and kinetics of cation ordering in MgAl2O4 spinel up to 1600 °C from in situ neutron diffraction
TL;DR: In this paper, the temperature dependence of the cation distribution in synthetic spinel (MgAl 2O4) was determined using in-situ time-of-flight neutron powder diffraction.