Does Local Disorder Occur in the Pyrochlore Zirconates?

Blanchard, Peter E. R.; Clements, R.; Kennedy, Brendan J.; Ling, Chris D.; Reynolds, Emily; Avdeev, Maxim; Stampfl, A. P. J.; Zhang, Zhaoming; Jang, Ling‐Yun

doi:10.1021/ic301677b

Cited by 104 publications

(118 citation statements)

References 52 publications

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“…In both the lowest-energy A 2 B 2 O 7 -fluorite and weberite-type structures the average number of oxygen ions surrounding Zr (Ho) is 6.5 (7.5), compared to the number of 7 that would characterize a random distribution. This preference for lower (higher) coordination around the B 4+ (A 3+ ) cation is consistent with reverse Monte Carlo (RMC) analysis from neutron total scattering7 and X-ray absorption experiments2930 on zirconate and hafnate systems (i.e., A 2 B 2 O 7 , B=Zr, Hf), with a general trend towards increasing (decreasing) oxygen ion coordination of B (A) as the A cation size decreases (this trend is discussed in further detail in the next section). Similar coordination behavior was also found for titanate systems31; however, the local order was found to be pyrochlore, which is distinctly different compared to the preferred weberite-type configuration found here and in ref.…”

Section: Resultssupporting

confidence: 79%

Chemical ordering in substituted fluorite oxides: a computational investigation of Ho2Zr2O7 and RE2Th2O7 (RE=Ho, Y, Gd, Nd, La)

Solomon

Shamblin

Lang

et al. 2016

Sci Rep

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Fluorite-structured oxides find widespread use for applications spanning nuclear energy and waste containment, energy conversion, and sensing. In such applications the host tetravalent cation is often partially substituted by trivalent cations, with an associated formation of charge-compensating oxygen vacancies. The stability and properties of such materials are known to be influenced strongly by chemical ordering of the cations and vacancies, and the nature of such ordering and associated energetics are thus of considerable interest. Here we employ density-functional theory (DFT) calculations to study the structure and energetics of cation and oxygen-vacancy ordering in Ho2Zr2O7. In a recent neutron total scattering study, solid solutions in this system were reported to feature local chemical ordering based on the fluorite-derivative weberite structure. The calculations show a preferred chemical ordering qualitatively consistent with these findings, and yield values for the ordering energy of 9.5 kJ/mol-cation. Similar DFT calculations are applied to additional RE2Th2O7 fluorite compounds, spanning a range of values for the ratio of the tetravalent and trivalent (RE) cation radii. The results demonstrate that weberite-type order becomes destabilized with increasing values of this size ratio, consistent with an increasing energetic preference for the tetravalent cations to have higher oxygen coordination.

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Section: Resultssupporting

confidence: 79%

Chemical ordering in substituted fluorite oxides: a computational investigation of Ho2Zr2O7 and RE2Th2O7 (RE=Ho, Y, Gd, Nd, La)

Solomon

Shamblin

Lang

et al. 2016

Sci Rep

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“…However, most of these pyrochlores are known to form disordered fluorite at high temperatures (see also Fig. 2 and the relevant text) and show experimental evidence for partial disordering [57], which is rather consistent with our result. The clear correlation of the smallness and negativeness of the AFP DFEs with the formation of the disordered fluorite strongly suggests that the easiness of defect formation on the oxygen sublattice is essential to the disordering of the pyrochlores and for subsequent formation of disordered fluorites.…”

supporting

confidence: 91%

Defect formation energies in A 2 B 2 O 7 pyrochlores

Kowalski

Beridze

et al. 2015

Scripta Materialia

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“…Small deformations of the Bragg peaks have nevertheless been observed by means of diffuse neutron scattering experiments, which correspond to a local volume variation at the Pr site of about 1‰. These inhomogeneities, even small, could affect the magnetic properties, due to the sensitivity of non-Kramers doublets to local perturbations [4,[40][41][42]. Further studies are ongoing to investigate in details these inhomogeneities and their consequences.…”

Section: A Crystal Growthmentioning

confidence: 99%

Antiferroquadrupolar correlations in the quantum spin ice candidatePr2Zr2O7

et al. 2016

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(2016) Antiferroquadrupolar correlations in the quantum spin ice candidate Pr2Zr2O7. Physical Review B, 94 (16). 165153 Permanent WRAP URL: http://wrap.warwick.ac.uk/87826 Copyright and reuse:The Warwick Research Archive Portal (WRAP) makes this work by researchers of the University of Warwick available open access under the following conditions. Copyright © and all moral rights to the version of the paper presented here belong to the individual author(s) and/or other copyright owners. To the extent reasonable and practicable the material made available in WRAP has been checked for eligibility before being made available.Copies of full items can be used for personal research or study, educational, or not-for-profit purposes without prior permission or charge. Provided that the authors, title and full bibliographic details are credited, a hyperlink and/or URL is given for the original metadata page and the content is not changed in any way. Publisher statement: © 2016 American Physical Society A note on versions:The version presented here may differ from the published version or, version of record, if you wish to cite this item you are advised to consult the publisher's version. Please see the 'permanent WRAP URL' above for details on accessing the published version and note that access may require a subscription. We present an experimental study of the quantum spin ice candidate pyrochlore compound Pr 2 Zr 2 O 7 by means of magnetization measurements, specific heat, and neutron scattering up to 12 T and down to 60 mK. When the field is applied along the [111] and [110] directions, k = 0 field-induced structures settle in. We find that the ordered moment rises slowly, even at very low temperature, in agreement with macroscopic magnetization. Interestingly, for H [110], the ordered moment appears on the so-called α chains only. The spin excitation spectrum is essentially inelastic and consists in a broad flat mode centered at about 0.4 meV with a magnetic structure factor which resembles the spin ice pattern. For H [110] (at least up to 2.5 T), we find that a well-defined mode forms from this broad response, whose energy increases with H , in the same way as the temperature of the specific-heat anomaly. We finally discuss these results in the light of mean field calculations and propose an interpretation where quadrupolar interactions play a major role, overcoming the magnetic exchange. In this picture, the spin ice pattern appears shifted up to finite energy because of those interactions. We then propose a range of acceptable parameters for Pr 2 Zr 2 O 7 that allow to reproduce several experimental features observed under field. With these parameters, the actual ground state of this material would be an antiferroquadrupolar liquid with spin-ice-like excitations.

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Does Local Disorder Occur in the Pyrochlore Zirconates?

Cited by 104 publications

References 52 publications

Chemical ordering in substituted fluorite oxides: a computational investigation of Ho2Zr2O7 and RE2Th2O7 (RE=Ho, Y, Gd, Nd, La)

Chemical ordering in substituted fluorite oxides: a computational investigation of Ho2Zr2O7 and RE2Th2O7 (RE=Ho, Y, Gd, Nd, La)

Defect formation energies in A 2 B 2 O 7 pyrochlores

Antiferroquadrupolar correlations in the quantum spin ice candidatePr2Zr2O7

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