Novel potentials for modelling defect formation and oxygen vacancy migration in Gd2Ti2O7 and Gd2Zr2O7 pyrochlores

Gunn, David S. D.; Allan, Neil L.; Foxhall, Henry R.; Harding, John H.; Purton, John A.; Smith, William R.; Stein, Michael J.; Todorov, Ilian T.; Travis, Karl P.

doi:10.1039/c2jm15264a

Cited by 41 publications

(17 citation statements)

References 33 publications

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“…29, we compare to calculations performed with a recent parameterization by Gunn et al, 41 and referred to here simply as "Gunn". The results from simulations performed using the Gunn parameterization are presented in Fig.…”

Section: Comparison With Another Potential Parameterizationmentioning

confidence: 99%

Structural vs. intrinsic carriers: contrasting effects of cation chemistry and disorder on ionic conductivity in pyrochlores

Perriot

Uberuaga

2015

J. Mater. Chem. A

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We use molecular dynamics simulations to investigate the role of cation disorder on oxygen diffusion in Gd 2 Zr 2 O 7 (GZO) and Gd 2 Ti 2 O 7 (GTO) pyrochlores, a class of complex oxides which contain a structural vacancy relative to the basic fluorite structure. The introduction of disorder has distinct effects depending on the chemistry of the material, increasing the mobility of structural carriers by up to four orders of magnitude in GZO. In contrast, in GTO, there is no mobility at zero or low disorder on the ns timescale, but higher disorder liberates the otherwise immobile carriers, allowing diffusion with rates comparable to GZO for the fully disordered material. We show that the cation disorder enhances the diffusivity by both increasing the concentration of mobile structural carriers and their individual mobility.The disorder also influences the diffusion in materials containing intrinsic carriers, such as additional vacancies V O or oxygen interstitials O I . While in ordered GZO and GTO the contribution of the intrinsic carriers dominates the overall diffusion of oxygen, O I in GZO contributes along with structural carriers, and the total diffusion rate can be calculated by assuming simple additive contributions from the two sources. Although the disorder in the materials with intrinsic defects usually enhances the diffusivity as in the defect-free case, in low concentrations, cation antisites A B or B A , where A ¼ Gd and B ¼ Zr or Ti, can act as traps for fast intrinsic defects. The trapping results in a lowering of the diffusivity, and causes a non-monotonic behavior of the diffusivity with disorder. By contrast, in the case of slow intrinsic defects, the main effect of the disorder is to liberate the structural carriers, resulting in an increase of the diffusivity regardless of the defect trapping.

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Section: Comparison With Another Potential Parameterizationmentioning

confidence: 99%

Structural vs. intrinsic carriers: contrasting effects of cation chemistry and disorder on ionic conductivity in pyrochlores

Perriot

Uberuaga

2015

J. Mater. Chem. A

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“…31 DL-FIND is distributed with ChemShell but is also available as a standalone open source library with a well-defined interface for use with other codes. It has been interfaced to QM codes such as GAMESS-UK, CRYSTAL, and CASTEP as well as MM routines from DL_POLY 32 and Tinker. 33…”

Section: Geometry Optimization With Dl-findmentioning

confidence: 99%

ChemShell—a modular software package for QM/MM simulations

Metz

Kästner

Sokol

et al. 2013

WIREs Comput Mol Sci

437

228

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1ChemShell is a modular computational chemistry package with a particular focus on hybrid quantum mechanical/molecular mechanical (QM/MM) simulations. A core set of chemical data handling modules and scripted interfaces to a large number of quantum chemistry and molecular modeling packages underpin a flexible QM/MM scheme. ChemShell has been used in the study of small molecules, molecular crystals, biological macromolecules such as enzymes, framework materials including zeolites, ionic solids, and surfaces. We outline the range of QM/MM coupling schemes and supporting functions for system setup, geometry optimization, and transition-state location (including those from the open-source DL-FIND optimization library). We discuss recently implemented features allowing a more efficient treatment of long range electrostatic interactions, X-ray based quantum refinement of crystal structures, free energy methods, and excited-state calculations. ChemShell has been ported to a range of parallel computers and we describe a number of options including parallel execution based on the message-passing capabilities of the interfaced packages and taskfarming for applications in which a number of individual QM, MM, or QM/MM calculations can performed simultaneously. We exemplify each of the features by brief reference to published applications. C

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“…The local structure of synthetic pyrochlore-type materials have been extensively studied by Raman spectroscopy and the observed Raman signals could be assigned to certain phonon modes on the basis of model calculations [6,7,10,45,48,49,52,[58][59][60][61][62][63][64][65][66][67][68][69][70][71].…”

Section: Hementioning

confidence: 99%

Thermal annealing of natural, radiation-damaged pyrochlore

Zietlow

Beirau

Mihailova

et al. 2016

Zeitschrift Für Kristallographie - Crystalline Materials

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Radiation damage in minerals is caused by the α-decay of incorporated radionuclides, such as U and Th and their decay products. The effect of thermal annealing (400-1000 K) on radiation-damaged pyrochlores has been investigated by Raman scattering, X-ray powder diffraction (XRD), and combined differential scanning calorimetry/thermogravimetry (DSC/TG). The analysis of three natural radiation-damaged pyrochlore samples from Miass/Russia [6.4 wt% Th, 23.1 · 10 18 α-decay events per gram (dpg)], Panda Hill/Tanzania (1.6 wt% Th, 1.6 · 10 18 dpg), and Blue River/Canada (10.5 wt% U, 115.4 · 10 18 dpg), are compared with a crystalline reference pyrochlore from Schelingen (Germany). The type of structural recovery depends on the initial degree of radiation damage (Panda Hill 28 %, Blue River 85 % and Miass 100 % according to XRD), as the recrystallization temperature increases with increasing degree of amorphization. Raman spectra indicate reordering on the local scale during annealing-induced recrystallization. As Raman modes around 800 cm −1 are sensitive to radiation damage . The most radiation damaged pyrochlore (Miass) shows an abrupt recovery of both, its short-(Raman) and long-range order (X-ray) between 800 and 850 K, while the weakly damaged pyrochlore (Panda Hill) begins to recover at considerably lower temperatures (near 500 K), extending over a temperature range of ca. 300 K, up to 800 K (Raman). The pyrochlore from Blue River shows in its initial state an amorphous X-ray diffraction pattern superimposed by weak Bragg-maxima that indicates the existence of ordered regions in a damaged matrix. In contrast to the other studied pyrochlores, Raman spectra of the Blue River sample show the appearance of local modes above 560 K between 700 and 800 cm −1 resulting from its high content of U and Ta impurities. DSC measurements confirmed the observed structural recovery upon annealing. While the annealing-induced ordering of Panda Hill begins at a lower temperature (ca. 500 K) the recovery of the highly-damaged pyrochlore from Miass occurs at 800 K. The Blue-River pyrochlore shows a multi-step recovery which is similarly seen by XRD. Thermogravimetry showed a continuous mass loss on heating for all radiation-damaged pyrochlores (Panda Hill ca. 1 %, Blue River ca. 1.5 %, Miass ca. 2.9 %).

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Novel potentials for modelling defect formation and oxygen vacancy migration in Gd2Ti2O7 and Gd2Zr2O7 pyrochlores

Cited by 41 publications

References 33 publications

Structural vs. intrinsic carriers: contrasting effects of cation chemistry and disorder on ionic conductivity in pyrochlores

Structural vs. intrinsic carriers: contrasting effects of cation chemistry and disorder on ionic conductivity in pyrochlores

ChemShell—a modular software package for QM/MM simulations

Thermal annealing of natural, radiation-damaged pyrochlore

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