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1753328 
Journal Article 
On the crystal structure of pyrochlores: Mossbauer spectra of orthorhombic CsFe2F6 and X-ray single crystal studies of the cubic compounds CsMgGaF6, (CsMVF6)-V-II-F-III (M-II = Mn, Zn), (CsMFeF6)-Fe-II-F-III (M-II = Mn, Cu, Zn), and Cs4Cu5V3O2F19 
Baum, E; Dahlke, P; Kaiser, V; Molinier, M; Schmidt, RE; Pebler, J; Massa, W; Babel, D 
2006 
1 
Zeitschrift fuer Anorganische und Allgemeine Chemie
ISSN: 0044-2313 
632 
14 
2244-2250 
WOS:000241548700016 
Orthorhombic CsFe2F6 (a = 749.1(3), b = 723.8(3), c = 1043.1(6) pm; V = 565.6(9) angstrom(3), Z = 4, Imma ?) was prepared with strongly Fe-57 doped FeF3 and its Mossbauer spectra measured. It is in accordance with the spectra of a natural 57 Fe abundance sample, also with respect to the intensity ratio (FeFeIII)-Fe-II = 1:1. For the formation of an ordered pyrochlore structure in spite of quenching thus an electronically induced phase transition should be responsible, explaining the M-II/M-III order observed in all mixed valence pyrochlores A(I)M(II)M(III)F(6). By contrast, single crystals of CsMgGaF6 (a = 1021.6(1)pm), CsMnVF6 (a = 1058.9(1) pm), CsMnFeF6 (a = 1054.6(1) pm), CsZnVF6 (a = 1041.5(1) pm, CsZnFeF6 (a = 1042.1 (1) pm) and CsCuFeF6 (a = 1037.7(2) pm), obtained by solid state reaction and slow cooling, all exhibit the cubic pyrochlore structure of the RbNiCrF6 type (Z = 8, Fd (3) over barm), in which the cations M-II/M-III are disordered in position (16c). An oxidfluoride of approximate composition Cs4Cu5V3O2F19 (a = 1022.2(1) pm) has the same structure, but in addition it shows a disordered occupation of the position (48f) by lack of about 1/8 of anions. Structural relations and distances for the cubic crystal structures refined (R between 0.02 and 0.06) are discussed. 
structure determination; Mossbauer spectra; pyrochlore; disorder; cesium; copper; vanadium; iron; oxides; fluorides