Die Struktur einiger Fluoride, Oxide und Oxidfluoride: der RbNiCrF6‐Typ

Babel, D.; Pausewang, G.; Viebahn, W.

doi:10.1002/ange.19680800516

Cited by 4 publications

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“…To indicate the type of ordering the occupancies of the four equipoints will be written in the order 16(c)l16(4(48( f)/8(a), soth at the formula A2B2(X6)Y will refer to arrangement I, A2B2(X5Y)X to arrangement II, while A2B2-(X6Y) will represent a statistical distribution of X and Y over 48(f) + 8(a), type III. This symbolism is easily extended to compositions A2B2X7-.YC, 0 < E 5 7. In 'inverse' pyrochlore compositions of the type RbNiCrF6 = B2-B3+X6M1+ reported by Babel et al (14) For personal use only. investigation of thallium antimonates5) a large cation M = K, Rb, Cs is located in 8(a) while the 16(c) sites are vacant: C2B2(F6)M; a variety of P phases of this type have been investigated since (9,(17)(18)(19)(20)(21)(22).…”

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Pyrochlores. X. Madelung energies of pyrochlores and defect fluorites

Barker¹,

White²,

Knop³

1976

Can. J. Chem.

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KNOP. Can. 3. Chem. 54, 2316 (1976. Electrostatic (Madelung) lattice energies have been calculated for a wide range of compounds A2B2X6Y with the pyrochlore-type structure. The cases of disorder and partial disorder on the non-metal sites have been examined, as well as the inverse case. where Y is a positive ion. The results of the calculations are compared with those for defect fluorite structure and an attempt is made to relate them to the conditions under which the pyrochlore phase is found. The effect of the site potential in restricting the existence boundaries of the pyrochlore phase is examined, as the potential must have the correct sign relative to the charge occupying the site. Alternative pyrochlore arrangements in which the 8(b) or 32(e) equipoints are occupied have also been explored. Recent interest in synthetic pyrochlore (P) phases in which oxygen is partially replaced by fluorine (2-10) prompts us to report briefly the results of our Madelung energy calculations for such compounds as well as for purely oxidic and purely fluoride pyro~hlores.~ In the idealized crystal structure of a 'classical' pyrochlore A2B2X6Y (space group Fd3n1. origin at centre in 16(c); Sleight's (12) case Ao) the metal atoms are in 16(c) (0, 0, 0; etc.) and 16(d) (-:, -B, -4 ; etc.) and the nonmetal atoms in 8(a)

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“…I t was proposed again. independently, for P phases of other compositions only in 1967 (14). Unfortunately only a small portion of Schrewelius's results has been published (16).…”

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Pyrochlores. X. Madelung energies of pyrochlores and defect fluorites

Barker¹,

White²,

Knop³

1976

Can. J. Chem.

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“…The structural analogs of the A x MF 3 compounds [7] include: cubic perovskite (SrTiO 3 ) and rhenium oxide (ReO 3 ) (x = 1.0, γ phase, each belonging to space group Pm3m = #221) [20]; hexagonal tungsten bronze (HTB) (x = 0.167 to x = 0.31, α phase, space group P6 3 /mcm = #185) [21]; tetragonal tungsten bronze (TTB) (x = 0.45 to x = 0.60, β phase, space group P4/mbm = #127) [22] or hexagonal BaTa 2 O 6 (x = 0.43 to x = 0.52, β phase, space group P6/mmm = #191 [21], which is a structure similar to TTB [23]; and finally modified pyrochlore (MP) (x = 0.45 to x = 0.58, δ phase, space group Fd3m = #227) [24]. The value of x alone cannot discriminate between the β phase and the δ phase [7].…”

Section: Reconstructive Transitionsmentioning

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Descent in Symmetry during Solid State Transitions and Other Anomalies in Mixed Valence Compounds AxMxⅡM1-xⅢF3 (A = K, Rb, Cs; M = V, Cr; x = 0.0 - 1.0)

Boo¹,

Mattern²,

Metzger³

2019

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The scope of solid-state transitions, from melting temperatures down to 4.2 K, is described for six systems: K x VF 3 , Rb x VF 3 , Cs x VF 3 , K x CrF 3 , Rb x CrF 3 , and Cs x CrF 3 (for x = 0.0 to 1.0). Connections are drawn between the compounds' compositions and structures with the various transitions and ordering events. Upon solidification from the melt and gradual cooling to room temperature, a sequential descent of symmetry appears to occur, from high-symmetry perovskite phases, through possible reconstructive transitions, to phases designated α, β, and δ, within which ionic ordering finally sets in, forming many new lower-symmetry structures. Many stable new structures are seen at room temperature. Finally, at cryogenic temperatures, magnetic ordering sets in. Other anomalies for these systems are also described. The analysis underscores the overall correspondence of structure, composition, and magnetic properties in these compounds. This lowering of symmetry mirrors what has been chronicled for oxygen-bearing perovskites that have yielded so many high-temperature ceramic superconductors.

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“…Além dos pirocloros com estequiometria completa, são conhecidos diversos pirocloros de defeito, com estequiometria A 2 B 2 X 6 [2], AB 2 X 6 [9]- [12] e A 2 B 2 X 6 X 1−y [13], nos quais nem todos os sítios são ocupados. A Fig.…”

Section: A Estrutura De Piroclorounclassified

Pressure-induced Phase Transitions in Defect Pyrochlores

Prottoni¹,

Jornada²

2013

Sci. cum Ind.

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In this paper the influence of pressure and temperature on four compounds with defect pyrochlore structure (NH4NbWO6, RbNbWO6, CsNbWO6, and p-WO3) is explored by means of X-ray diffraction, vibrational (Raman and infrared absorption) spectroscopy and computer simulations. Several structural transitions were observed, including an unusual insertion reaction with volume increase at high pressures. This latter transition is further explored to reveal the influence on the transition pressure of the nature and ionic radius of the cation residing inside the cages formed by the pyrochlore framework. http://dx.doi.org/10.18226/23185279.v1iss1p24

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Die Struktur einiger Fluoride, Oxide und Oxidfluoride: der RbNiCrF₆‐Typ

Cited by 4 publications

References 0 publications

Pyrochlores. X. Madelung energies of pyrochlores and defect fluorites

Pyrochlores. X. Madelung energies of pyrochlores and defect fluorites

Descent in Symmetry during Solid State Transitions and Other Anomalies in Mixed Valence Compounds A<sub>x</sub>M<sub>x</sub><sup style="margin-left:-10px;">Ⅱ</sup>M<sub>1-x</sub><sup style="margin-left:-16px;">Ⅲ</sup>F<sub>3</sub> (A = K, Rb, Cs; M = V, Cr; x = 0.0 - 1.0)

Pressure-induced Phase Transitions in Defect Pyrochlores

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