The oxygen positional parameter in pyrochlores and its dependence on disorder

Minervini, Licia; Grimes, Robin W.; Tabira, Yasunori; Withers, Raymond; Sickafus, Kurt E.

doi:10.1080/01418610208240001

Cited by 77 publications

(43 citation statements)

References 32 publications

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“…[16][17][18][19] While not shown, we observe that our calculated x parameters for zirconate, hafnate, titanate, and stannate pyrochlores decrease monotonically and linearly with increasing A 3+ size, which is in agreement with our previous study. 32 Assuming ideal configurational entropy of mixing for the Remarkably, the experimentally observed ranking of T O−D ͑Gd 2 Zr 2 O 7 Ͻ Sm 2 Zr 2 O 7 Ͻ Tb 2 Hf 2 O 7 Ͻ Nd 2 Zr 2 O 7 Ϸ Gd 2 Hf 2 O 7 ͒ is correctly predicted by our calculations, although on average we underestimate the experimental data by ϳ250 K. This good agreement confirms the suitability of using the SQS approach to model the disordered state of pyrochlores. The remaining quantitative discrepancy may be due to experimental uncertainties, the inaccuracies of GGA, or to the neglect of nonconfigurational ͑vibrational, electronic, etc.͒ entropies in our estimations.…”

Section: Lattice Vectorsmentioning

confidence: 97%

First-principles prediction of disordering tendencies in pyrochlore oxides

et al. 2009

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Using first-principles calculations, we systematically predict the order-disorder energetics of series of zirconate ͑A 2 Zr 2 O 7 ͒, hafnate ͑A 2 Hf 2 O 7 ͒, titanate ͑A 2 Ti 2 O 7 ͒, and stannate ͑A 2 Sn 2 O 7 ͒ pyrochlores. The disordered defect-fluorite structure is modeled using an 88-atom two-sublattice special quasirandom structure ͑SQS͒ that closely reproduces the most relevant near-neighbor intrasublattice and intersublattice pair-correlation functions of the random mixture. The order-disorder transition temperatures of these pyrochlores estimated from our SQS calculations show overall good agreement with existing experiments. We confirm previous studies suggesting that the bonding in pyrochlores is not purely ionic and thus electronic effects also play a role in determining their disordering tendencies. Our results have important consequences for numerous applications, including nuclear waste forms and fast ion conductors.A 2 B 2 O 7 pyrochlores are an important class of oxide materials that are being considered for nuclear applications including the immobilization of actinides in nuclear waste 1-3 and inert matrix fuel. 4,5 The pyrochlore structure ͑space group Fd3m͒ is closely related to the fluorite structure ͑space group Fm3m͒ and can be considered as an ordered fluorite derivative, i.e., BO 2 fluorite with half of the tetravalent B 4+ cations replaced by trivalent A 3+ accompanied by chargecompensating structural oxygen vacancies. Here both the cations and anions are fully ordered such that each A 3+ ͑B 4+ ͒ cation is coordinated by eight ͑six͒ nearest-neighbor oxygen atoms. The pyrochlore structure can be transformed into the disordered defect-fluorite structure by randomly distributing the cations and anions on their respective sublattices.As a nuclear material, the host must be highly resistant to radiation damage. This is because irradiation will create atomic scale defects, which with time will accumulate, possibly leading to amorphization and/or microcracking of the crystalline structure. The two most important atomistic defects that are created in A 2 B 2 O 7 pyrochlore oxides when exposed to displacive radiation damage conditions are cation antisite defects ͑0 → A B + B A ͒ and anion Frenkel pairs ͑0 → V O +O i ͒. 6,7 Interestingly, these defects are precisely the ones that are responsible for the pyrochlore to fluorite orderdisorder transformation. In other words, radiation damage inherently involves disordering processes ͑for example, neutron-diffraction measurements showed that the Mg and Al sublattices in MgAl 2 O 4 spinel are fully disordered after high-fluence neutron irradiation 8 ͒. Our earlier studies 2,3 found that oxides that show a natural propensity to accommodate lattice disorder will be less susceptible to detrimental radiation damage effects such as amorphization. Therefore, the order-disorder phase transition under equilibrium condition is the focus of this work. An understanding of structural disorder is also important for other properties such as ionic conductivity. 9,10 A...

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Section: Lattice Vectorsmentioning

confidence: 97%

First-principles prediction of disordering tendencies in pyrochlore oxides

et al. 2009

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“…The NDZ parameters are taken from Minervini et al [13] The Mg-O parameters were determined for this study by Professor Robin Grimes, and specifically designed to be compatible with the NDZ parameters, thereby allowing the simulation of MgO-NDZ cercers, the subject of ongoing work. The interatomic potentials are fitted to the experimental lattice parameters at room-temperature for MgO and NDZ.…”

Section: Thermal Expansion Of Mgo and Ndzmentioning

confidence: 99%

Thermal transport properties of MgO and Nd2Zr2O7 pyrochlore by molecular dynamics simulation

Shukla

Watanabe

Nino

et al. 2008

Journal of Nuclear Materials

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“…Alternatively, if the antisite defect is large (e.g., Gd 2 Ti 2 O 7 ) then there is an irradiation-induced crystalline to amorphous transition. The cation antisite defect energies are smaller the closer these ions are in size [35,36].…”

Section: The Potential Parameters For O-o Ti-o Gd-o and Zr-o Collementioning

confidence: 99%

Use of massively parallel molecular dynamics simulations for radiation damage in pyrochlores

et al. 2007

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DL_POLY_3 is a general purpose molecular dynamics (MD) simulation package designed to simulate systems of the order of tens of millions of particles and beyond by efficiently harnessing the power of modern computer clusters. Here we discuss the package design, functionality and report on performance and capability limits. We then report the application of DL_POLY_3 to study radiation cascades in Gd 2 Ti 2 O 7 and Gd 2 Zr 2 O 7 , potential materials for high-level radioactive waste storage and discuss problems associated with the analysis of the cascades. We see little direct amorphisation but rather the start of a transition to the fluorite structure which is more pronounced for the Zr than the Ti compound.

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The oxygen positional parameter in pyrochlores and its dependence on disorder

Cited by 77 publications

References 32 publications

First-principles prediction of disordering tendencies in pyrochlore oxides

First-principles prediction of disordering tendencies in pyrochlore oxides

Thermal transport properties of MgO and Nd2Zr2O7 pyrochlore by molecular dynamics simulation

Use of massively parallel molecular dynamics simulations for radiation damage in pyrochlores

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