Tolerance factor for pyrochlores and related structures

Mouta, Rodolpho; Silva, R. X.; Paschoal, C. W. A.

doi:10.1107/s2052519213020514

Cited by 58 publications

(39 citation statements)

References 88 publications

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“…However, if these displacements are due to A / B cation size mismatch they exist in all pyrochlores and not only resolve several long standing issues, such as the discrepancy between experimental and calculated pyrochlore lattice parameters 5, 48–51 , but also many recently contested issues 11, 25, 42 . Since the A -Oʹ bond distance appears longer, these conclusions indicate that the bond valence sums, which were revised for the bonding coordination in these compounds 52 , may need to be updated.…”

Section: Discussionmentioning

confidence: 99%

Universal geometric frustration in pyrochlores

et al. 2018

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Materials with the pyrochlore/fluorite structure have diverse technological applications, from magnetism to nuclear waste disposal. Here we report the observation of structural instability present in the pyrochlores A2Zr2O6Oʹ (A = Pr, La) and Yb2Ti2O6Oʹ, that exists despite ideal stoichiometry, ideal cation-ordering, the absence of lone pair effects, and a lack of magnetic order. Though these materials appear to have good long-range order, local structure probes find displacements, of the order of 0.01 nm, within the pyrochlore framework. The pattern of displacements of the A2Oʹ sublattice mimics the entropically-driven fluxional motions characteristic of and well-known in the silica mineral β-cristobalite. The universality of such displacements within the pyrochlore structure adds to the known structural diversity and explains the extreme sensitivity to composition found in quantum spin ices and the lack of ferroelectric behavior in pyrochlores.

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Section: Discussionmentioning

confidence: 99%

Universal geometric frustration in pyrochlores

et al. 2018

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“…A recent analysis of the pyrochlore structural data 15 allowed introducing a new empirical tolerance factor for the representatives of this group of compounds. So, modeling of the crystal lattice constants and structures has never stopped and still appears to be an interesting and attractive problem fundamental and applied importance.…”

Section: Introductionmentioning

confidence: 99%

Lattice Parameters and Stability of the Spinel Compounds in Relation to the Ionic Radii and Electronegativities of Constituting Chemical Elements

2014

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A thorough consideration of the relation between the lattice parameters of 185 binary and ternary spinel compounds, on one side, and ionic radii and electronegativities of the constituting ions, on the other side, allowed for establishing a simple empirical model and finding its linear equation, which links together the above-mentioned quantities. The derived equation gives good agreement between the experimental and modeled values of the lattice parameters in the considered group of spinels, with an average relative error of about 1% only. The proposed model was improved further by separate consideration of several groups of spinels, depending on the nature of the anion (oxygen, sulfur, selenium/tellurium, nitrogen). The developed approach can be efficiently used for prediction of lattice constants for new isostructural materials. In particular, the lattice constants of new hypothetic spinels ZnRE 2 O 4 , CdRE 2 S4, CdRE 2 Se 4 (RE=rare earth elements) are predicted in the present paper. In addition, the upper and lower limits for the variation of the ionic radii, electronegativities and certain their combinations were established, which can be considered as stability criteria for the spinel compounds. The findings of the present paper offer a systematic overview of the structural properties of spinels and can serve as helpful guides for synthesis of new spinel compounds.3

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“…Such structural evolution is due to the difference in their ionic radii of metal cations [30]. From the literature survey, there are different structural reports are available for BBFO viz., Rhombohedral (R3c) [13,14], Tetragonal (P4 mm) [12,31] and Cubic (Pm-3m) [29].…”

Section: X-ray Diffraction (Xrd)mentioning

confidence: 99%