Point Defects in Solids: Physics, Chemistry, and Thermodynamics

Kröger, F. A.

doi:10.1029/gm031p0001

Cited by 7 publications

(1 citation statement)

References 88 publications

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“…However, another possible co-precipitation mechanism is the incorporation of the foreign ion into a preexisting defect in the crystal structure. Crystalline solids in thermodynamic equilibrium all contain defects due to local disorder, non-stoichiometry, and the presence of aliovalent impurity ions (KRÖGER, 1985). One example of such a point defect is a vacancy.…”

Section: Incorporation and Defectsmentioning

confidence: 99%

Uranyl (VI) and neptunyl (V) incorporation in carbonate and sulfate minerals: Insight from first-principles

Walker

Becker

2015

Geochimica et Cosmochimica Acta

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The incorporation of radionuclides into low-temperature mineral hosts may strongly influence the concentration and migration of radioactive contaminants in the subsurface. One difficulty in evaluating the thermodynamics of incorporation is that experiments are often performed at high supersaturations and typically do not reach equilibrium. An alternative way to obtain the equilibrium thermodynamics is the quantum-mechanical analysis of the mineral host and the incorporated species before and after incorporation. In this contribution, density functional theory is used to calculate the energetics, resulting structures, and electronic configuration of uranyl (UO 2 2+) and neptunyl (NpO 2 +) incorporation into sulfate and carbonate minerals. In each host mineral, gypsum (CaSO 4 2H 2 O), anhydrite (CaSO 4), anglesite (PbSO 4), celestine (SrSO 4), barite (BaSO 4), calcite (CaCO 3), aragonite (CaCO 3), cerussite (PbCO 3), strontianite (SrCO 3), and witherite (BaCO 3), a divalent cation is replaced with either UO 2 2+ or NpO 2 + (in the case of neptunyl, charge balance is maintained with an additional hydrogen ion). The source of the actinyl ion and the sink for the host cation are modeled as both solid and aqueous phases, the latter of which requires an expansion of previous descriptions of incorporation. By combining periodic and cluster computational methods, this newly-developed approach enables the quantum-mechanical simulation of reactions between charged, aqueous molecular species and solid mineral phases. Among the host minerals considered, gypsum and aragonite are the most favorable hosts for both uranyl and neptunyl uptake (∆E ୷୮,ୟ୯

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Section: Incorporation and Defectsmentioning

confidence: 99%

Uranyl (VI) and neptunyl (V) incorporation in carbonate and sulfate minerals: Insight from first-principles

Walker

Becker

2015

Geochimica et Cosmochimica Acta

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Solute carbon and carbon segregation in magnesium oxide single crystals ? a secondary ion mass spectrometry study

Freund

1986

Phys Chem Minerals

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Electrical properties of fine‐grained olivine: Evidence for grain boundary transport

et al. 2004

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[1] To investigate the mechanisms responsible for electrical conduction and deduce the relation between grain size and conductivity, the electrical conductivity of synthetic polycrystalline forsterite, with grain sizes between 1.1 ± 0.4 and 4.7 ± 2.4 mm, was measured at temperatures up to 1470°C and at 0.1 MPa pressure. The complex impedance plots display one clear arc, indicating a single dominant conduction mechanism. Bulk conductivity is inversely proportional to the grain size of the different samples. This relation suggests that the electrical conductivity of the samples is controlled by grain boundary diffusion of the charge carriers. The apparent activation energy (Q) for diffusion of the charge carriers between 1180°and 1470°C lies between 315 ± 39 and 323 ± 15 kJ/mol. This resembles previous data on grain boundary diffusion of Mg in forsterite. A geometrical model of less-conducting cubic grains and more-conducting grain boundaries agrees well with the experimental data. This model is applied to predict the conductivity contrast between fine-grained shear zones and less-deformed regions in the lithosphere. Upper mantle shear zones are predicted to have 1.5-2 orders of magnitude higher conductivity than less-deformed regions in the lithosphere. This means grain boundary transport probably has an important role in the existence of anomalously high conductivity zones in the upper mantle and that fine-grained shear zones might be detected using magnetotelluric methods.

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Point Defects in Solids: Physics, Chemistry, and Thermodynamics

Cited by 7 publications

References 88 publications

Uranyl (VI) and neptunyl (V) incorporation in carbonate and sulfate minerals: Insight from first-principles

Uranyl (VI) and neptunyl (V) incorporation in carbonate and sulfate minerals: Insight from first-principles

Solute carbon and carbon segregation in magnesium oxide single crystals ? a secondary ion mass spectrometry study

Electrical properties of fine‐grained olivine: Evidence for grain boundary transport

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