Inorganic Nonstoichiometric Crystalline Systems and Atomic Ordering

Smith, Mark E.

doi:10.1002/9780470034590.emrstm1044

Cited by 2 publications

(1 citation statement)

References 40 publications

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“…The chemical shift interaction is typically very sensitive to the coordination number, the nature of the next-nearest neighbour (NNN) environment and the local geometry. 13,14 Although a rich source of information, the complex spectra that result (particularly when more than one crystallographically-distinct species is present) are difficult to interpret, and in recent years there has been increasing interest in the use of density functional theory (DFT) calculations alongside experimental work. [15][16][17] The use of codes that exploit the inherent periodicity and translational symmetry of the solid state avoid the need to model a solid as a ''cluster'', breaking bonds and perturbing the local environment (and, consequently, varying the calculated NMR parameters).…”

Section: Introductionmentioning

confidence: 99%

New insights into phase distribution, phase composition and disorder in Y₂(Zr,Sn)₂O₇ ceramics from NMR spectroscopy

Ashbrook

Mitchell

Sneddon

et al. 2015

Phys. Chem. Chem. Phys.

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A combination of (89)Y and (119)Sn NMR spectroscopy and DFT calculations are used to investigate phase evolution, local structure and disorder in Y2Zr2-xSnxO7 ceramics, where a phase change is predicted, from pyrochlore to defect fluorite, with increasing Zr content. The ability of NMR to effectively probe materials that exhibit positional and compositional disorder provides insight into the atomic-scale structure in both ordered and disordered phases and, by exploiting the quantitative nature of the technique, we are able to determine detailed information on the composition of the phase(s) present and the average coordination number (and next-nearest neighbour environment) of the cations. In contrast to previous studies, a more complex picture of the phase variation with composition emerges, with single-phase pyrochlore found only for the Sn end member, and a single defect fluorite phase only for x = 0 to 0.6. A broad two-phase region is observed, from x = 1.8 to 0.8, but the two phases present have very different composition, with a maximum of 13% Zr incorporated into the pyrochlore phase, whereas the composition of the defect fluorite phase varies throughout. Preferential ordering of the anion vacancies in the defect fluorite phase is observed, with Sn only ever found in a six-coordinate environment, while remaining vacancies are shown to be more likely to be associated with Zr than Y. Our findings are then discussed in the light of those from previous studies, many of which utilize diffraction-based approaches, where, in most cases, a single phase of fixed composition has been assumed for the refinement procedure. The significant and surprising differences encountered demonstrate the need for complementary approaches to be considered for a detailed and accurate picture of both the long- and short-range structure of a solid to be achieved.

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Section: Introductionmentioning

confidence: 99%

New insights into phase distribution, phase composition and disorder in Y₂(Zr,Sn)₂O₇ ceramics from NMR spectroscopy

Ashbrook

Mitchell

Sneddon

et al. 2015

Phys. Chem. Chem. Phys.

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¹¹⁹Sn MAS NMR and first-principles calculations for the investigation of disorder in stannate pyrochlores

Mitchell

Reader

Johnston

et al. 2011

Phys. Chem. Chem. Phys.

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The local structure and cation disorder in Y(2)Ti(2-x)Sn(x)O(7) pyrochlores, materials proposed for the encapsulation of lanthanide- and actinide-bearing radioactive waste, is studied using (119)Sn (I = 1/2) NMR spectroscopy. NMR provides an excellent probe of disorder, as it is sensitive to the atomic scale environment without the need for any long-range periodicity. However, the complex and overlapping spectral resonances that often result can be difficult to interpret. Here, we demonstrate how (119)Sn DFT calculations can be used to aid the spectral interpretation and assignment, confirming that Sn occupies only the six-coordinate pyrochlore B site, and that the Sn chemical shift is sensitive to the number of Sn/Ti on the neighbouring B sites. Although distinct resonances are resolved experimentally when the Ti content is low, there is significant spectral overlap for Ti-rich compositions. We establish that this is a result of two competing contributions to the Sn chemical shift; an upfield shift resulting from the incorporation of the more polarizing Ti(4+) cation onto the neighbouring B sites, and a concomitant downfield shift arising from the decrease in unit cell size. Despite the considerably easier spectral acquisition, the lower resolution in the (119)Sn spectra hinders the extraction of the detailed structural information previously obtained using (89)Y NMR. However, the spectra we obtain are consistent with a random distribution of Sn/Ti on the pyrochlore B sites. Finally, we consider whether an equilibrium structure has been achieved by investigating materials that have been annealed for different durations.

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Inorganic Nonstoichiometric Crystalline Systems and Atomic Ordering

Cited by 2 publications

References 40 publications

New insights into phase distribution, phase composition and disorder in Y₂(Zr,Sn)₂O₇ ceramics from NMR spectroscopy

New insights into phase distribution, phase composition and disorder in Y₂(Zr,Sn)₂O₇ ceramics from NMR spectroscopy

¹¹⁹Sn MAS NMR and first-principles calculations for the investigation of disorder in stannate pyrochlores

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Inorganic Nonstoichiometric Crystalline Systems and Atomic Ordering

Cited by 2 publications

References 40 publications

New insights into phase distribution, phase composition and disorder in Y2(Zr,Sn)2O7 ceramics from NMR spectroscopy

New insights into phase distribution, phase composition and disorder in Y2(Zr,Sn)2O7 ceramics from NMR spectroscopy

119Sn MAS NMR and first-principles calculations for the investigation of disorder in stannate pyrochlores

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New insights into phase distribution, phase composition and disorder in Y₂(Zr,Sn)₂O₇ ceramics from NMR spectroscopy

New insights into phase distribution, phase composition and disorder in Y₂(Zr,Sn)₂O₇ ceramics from NMR spectroscopy

¹¹⁹Sn MAS NMR and first-principles calculations for the investigation of disorder in stannate pyrochlores