Pyrochlore Structural Chemistry: Predicting the Lattice Constant by the Ionic Radii and Electronegativities of the Constituting Ions

Brik, M.G.; Srivastava, A.M.

doi:10.1111/j.1551-2916.2012.05115.x

Cited by 73 publications

(54 citation statements)

References 14 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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“…Their unique properties such as magnetic behavior, conductivity31 and phase tolerance32 renderenormous applications in magnetic devices33, Li-O 2 battery34, solid state high temperature fuel cells (SOFC)35, nuclear waste immobilization36 and water splitting32 and so on. There are many pyrochlore iridates (A 2 Ir 2 O 7-δ ), but A when lanthanides (Nd-Yb) show a metal insulator or a metal insulator transition as a function of temperature33, thus they are out of our considerationas the electrical conductivity of a material is the fundamental factorfor an electrocatalyst.…”

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confidence: 99%

OER activity manipulated by IrO6 coordination geometry: an insight from pyrochlore iridates

Sun

Liu

Gong

et al. 2016

Sci Rep

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The anodic reaction of oxygen evolution reaction (OER), an important point for electrolysis, however, remains the obstacle due to its complicated reaction at electrochemical interfaces. Iridium oxide (IrO2) is the only currently known 5d transition metal oxide possessing admirable OER activity. Tremendous efforts have been carried out to enhance the activity of iridium oxides. Unfortunately there lies a gap in understanding what factors responsible for the activity in doped IrO2 or the novel crystal structure. Based on two metallic pyrochlores (Bi2Ir2O7 and Pb2Ir2O6.5) and IrO2. It has been found that there exists a strong correlation between the specific OER activity and IrO6 coordination geometry. The more distortion in IrO6 geometry ascends the activity of Ir sites, and generates activity order of Pb-Ir > IrO2 > Bi-Ir. Our characterizations reveal that distorted IrO6 in Pb-Ir induces a disappearance of J = 1/2 subbands in valence band, while Bi-Ir and IrO2 resist this nature probe. The performed DFT calculations indicated the distortion in IrO6 geometry can optimize binding strength between Ir-5d and O-2p due to broader d band width. Based on this insight, enhancement in OER activity is obtained by effects that change IrO6 octahedral geometry through doping or utilizing structural manipulation with nature of distorted octahedral coordination.

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“…X=tetravalent cation, Y=F, Cl, Br, I) 13 and cubic pyrochlores 14 were modeled with achieving good agreement between the predicted and experimental LCs values. A recent analysis of the pyrochlore structural data 15 allowed introducing a new empirical tolerance factor for the representatives of this group of compounds.…”

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

Self Cite

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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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Pyrochlore Structural Chemistry: Predicting the Lattice Constant by the Ionic Radii and Electronegativities of the Constituting Ions

Cited by 73 publications

References 14 publications

Universal geometric frustration in pyrochlores

Universal geometric frustration in pyrochlores

OER activity manipulated by IrO6 coordination geometry: an insight from pyrochlore iridates

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

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