ChemInform Abstract: Preparation and Crystal Structure of the Calcium Rhenate(VI, VII) Ca5Re3O15‐x.

Jeitschko, Wolfgang; Mons, Horst A.; Rodewald, Ute Ch.

doi:10.1002/chin.200016008

Cited by 3 publications

(3 citation statements)

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“…As shown in Figure , a 45° rotation of an SbO 6 octahedron will move 4 of the 6 oxygen atoms into interstitial positions while simultaneously vacating all four of the neighboring perovskite anion sites. Such 45° rotations of smaller B ′O 6 octahedra are known to occur in several anion stoichiometric double-perovskite compounds which also have very large size differences between the B and the B ′ cations and small tolerance factors. − One such compound is the closely related Sr 3 WO 6 . In such compounds the 45° rotations serve to increase the coordination numbers of the larger B -site cations.…”

Section: Resultsmentioning

confidence: 99%

Drastic Differences between the Local and the Average Structures of Sr₂MSbO_5.5 (M = Ca, Sr, Ba) Oxygen-Deficient Double Perovskites

2012

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For many disordered materials, knowing their average crystal structure is insufficient for explaining and predicting their macroscopic properties. It has been found that a description of the short-range atomic arrangements is needed to understand such materials. In order to understand the conduction pathways in ionic conductors which have random distributions of vacancies it is imperative to know the local structures which are present. In this study the local structures of three oxygen-deficient double perovskites, Sr(2)MSbO(5.5) (M = Ca, Sr, Ba), have been investigated by neutron pair distribution function analysis. The ions in these compounds are all found to have local coordination environments which are radically different than those given by their average structures. While there is no long-range ordering of the oxygen vacancies in these compounds, a considerable amount of short-range order does exist. The conditions which drive the short-range ordering are discussed as are the possible mechanisms for achieving it. It is proposed that the SbO(5) polyhedra form distorted trigonal bipyramids by moving oxygen atoms into interstitial positions. In the M = Sr compound 45° rotations of SbO(6) octahedra are also present, which add additional oxygen atoms into the interstitial sites. Large displacements of the Ca(2+), Sr(2+), and Ba(2+) cations are also present, the directions of which are correlated with the occupancies of the interstitial oxygen sites. Reverse Monte Carlo modeling of the pair distribution function data has provided the actual bond length distributions for the cations.

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Section: Resultsmentioning

confidence: 99%

Drastic Differences between the Local and the Average Structures of Sr₂MSbO_5.5 (M = Ca, Sr, Ba) Oxygen-Deficient Double Perovskites

2012

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“…This serves to increase the coordination environment of the larger B cations to values greater than 6. Other compounds which are known to display such patterns of noncooperative octahedral tilting include Rb 2 KCrF 6 , Rb 2 KGaF 6 , K 3 MoO 3 F 3 , Sr 3 WO 6 , Sr 3 TeO 6 , Ba 3 TeO 6 , and A 11 B 4 O 24 (A = Ca, Sr; B = Re, Os; some of the A-sites are vacant). − …”

Section: Introductionmentioning

confidence: 99%

The High-Temperature Polymorphs of K₃AlF₆

et al. 2011

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The crystal structures of the three high-temperature polymorphs of K(3)AlF(6) have been solved from neutron powder diffraction, synchrotron X-ray powder diffraction, and electron diffraction data. The β-phase (stable between 132 and 153 °C) and γ-phase (stable between 153 to 306 °C) can be described as unusually complex superstructures of the double-perovskite structure (K(2)KAlF(6)) which result from noncooperative tilting of the AlF(6) octahedra. The β-phase is tetragonal, space group I4/m, with lattice parameters of a = 13.3862(5) Å and c = 8.5617(3) Å (at 143 °C) and Z = 10. In this phase, one-fifth of the AlF(6) octahedra are rotated about the c-axis by ∼45° while the other four-fifths remain untilted. The large ∼45° rotations result in edge sharing between these AlF(6) octahedra and the neighboring K-centered polyhedra, resulting in pentagonal bipyramidal coordination for four-fifths of the K(+) ions that reside on the B-sites of the perovskite structure. The remaining one-fifth of the K(+) ions on the B-sites retain octahedral coordination. The γ-phase is orthorhombic, space group Fddd, with lattice parameters of a = 36.1276(4) Å, b = 17.1133(2) Å, and c = 12.0562(1) Å (at 225 °C) and Z = 48. In the γ-phase, one-sixth of the AlF(6) octahedra are randomly rotated about one of two directions by ∼45° while the other five-sixths remain essentially untilted. These rotations result in two-thirds of the K(+) ions on the B-site obtaining 7-fold coordination while the other one-third remain in octahedral coordination. The δ-phase adopts the ideal cubic double-perovskite structure, space group Fm ̅3m, with a = 8.5943(1) Å at 400 °C. However, pair distribution function analysis shows that locally the δ-phase is quite different from its long-range average crystal structure. The AlF(6) octahedra undergo large-amplitude rotations which are accompanied by off-center displacements of the K(+) ions that occupy the 12-coordinate A-sites.

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“…This structure is commonly written as A , all containing 4d and 5d transition metals in an exiguous structural family that, yet, presents a highly desirable framework for tuning chemical and physical properties. [18][19][20][21][22][23] Thereby, recently we have prepared and studied a novel Mocontaining framework with a strongly defective Sr 11 Mo 4 O 23 stoichiometry. 24,25 This material performs as an oxide-ion conductor, with a moderate ionic conductivity compared with conventional electrolyte oxides, but it opens up new possibilities on where to search for novel electrolyte materials.…”

Section: Introductionmentioning

confidence: 99%

Structural origin of the enhanced ionic conductivity upon Nb doping in Sr₁₁Mo₄O₂₃ defective double perovskite

et al. 2017

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We report a substantial enhancement of the oxide-ion conductivity in SrMoO achieved by Nb doping the Mo sites. This series responds to the formula: SrMoNbO (with x = 0.0, 0.5 and 1.0). The original structure can be related to the conventional double perovskite; however, it presents a broken corner sharing connectivity of the octahedral framework, hence leading to a complex and highly defective network. The samples were prepared via citrate precursor method, followed by thermal treatments at 1300 °C for 12 hours in air. The crystal structures were refined from X-ray and neutron powder diffraction (NPD) data. A phase transition from tetragonal to cubic symmetry is identified in a temperature-dependent NPD study, driven by an oxygen delocalization effect. The ionic conductivity measured by impedance spectroscopy is enhanced upon Nb-doping; the x = 1 doped phase exhibits a threefold increase compared to the pristine SrMoO oxide, with conductivity values of 7.6 × 10 and 2.7 × 10 S·cm at 650 and 800 °C, which are even greater than for YSZ in the 650-800 °C temperature range, and close to those reported for other state-of-the art solid-oxide electrolytes.

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ChemInform Abstract: Preparation and Crystal Structure of the Calcium Rhenate(VI, VII) Ca₅Re₃O_15‐x.

Cited by 3 publications

References 1 publication

Drastic Differences between the Local and the Average Structures of Sr₂MSbO_5.5 (M = Ca, Sr, Ba) Oxygen-Deficient Double Perovskites

Drastic Differences between the Local and the Average Structures of Sr₂MSbO_5.5 (M = Ca, Sr, Ba) Oxygen-Deficient Double Perovskites

The High-Temperature Polymorphs of K₃AlF₆

Structural origin of the enhanced ionic conductivity upon Nb doping in Sr₁₁Mo₄O₂₃ defective double perovskite

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ChemInform Abstract: Preparation and Crystal Structure of the Calcium Rhenate(VI, VII) Ca5Re3O15‐x.

Cited by 3 publications

References 1 publication

Drastic Differences between the Local and the Average Structures of Sr2MSbO5.5 (M = Ca, Sr, Ba) Oxygen-Deficient Double Perovskites

Drastic Differences between the Local and the Average Structures of Sr2MSbO5.5 (M = Ca, Sr, Ba) Oxygen-Deficient Double Perovskites

The High-Temperature Polymorphs of K3AlF6

Structural origin of the enhanced ionic conductivity upon Nb doping in Sr11Mo4O23 defective double perovskite

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ChemInform Abstract: Preparation and Crystal Structure of the Calcium Rhenate(VI, VII) Ca₅Re₃O_15‐x.

Drastic Differences between the Local and the Average Structures of Sr₂MSbO_5.5 (M = Ca, Sr, Ba) Oxygen-Deficient Double Perovskites

Drastic Differences between the Local and the Average Structures of Sr₂MSbO_5.5 (M = Ca, Sr, Ba) Oxygen-Deficient Double Perovskites

The High-Temperature Polymorphs of K₃AlF₆

Structural origin of the enhanced ionic conductivity upon Nb doping in Sr₁₁Mo₄O₂₃ defective double perovskite