51681-88-0Relevant articles and documents
Fluorination of Bi1.8Fe1.2SbO7 pyrochlore solid solutions
Egorysheva,Ellert,Gaitko,Brekhovskikh,Zhidkova,Maksimov, Yu. V.
, p. 962 - 968 (2017)
A technique has been developed for fluorinating the pyrochlore oxide Bi1.8Fe0.2FeSbO7, and a compound with the composition Bi1.8Fe1.2SbO7–x/2Fx has been obtained. The synthesized oxyfluoride also has the pyrochlore structure (sp. gr. Fd3m), with a lattice parameter a = 10.4443(1) ? (Rwp = 5.2). It has been shown that the charge balance upon fluorine substitution for oxygen is maintained not through partial reduction of Fe3+ to Fe2+ but through the incorporation of fluorine into oxygen vacancies. The magnetic behavior of the fluorinated pyrochlore phase is determined by the persisting frustration of the octahedral sublattice, which is responsible for the development of a spin glass state below Tf = 12 K. The fluorination-induced changes in the anion sublattice led to an increase in the antiferromagnetic exchange interaction between neighboring Fe3+ ions and changes in the dynamic properties of the spin glass phase.
The first example of a mixed valence ternary compound of silver with random distribution of Ag(i) and Ag(ii) cations
Mazej, Zoran,Micha?owski, Tomasz,Goreshnik, Evgeny A.,Jagli?i?, Zvonko,Ar?on, Iztok,Szyd?owska, Jadwiga,Grochala, Wojciech
, p. 10957 - 10968 (2015/06/25)
The reaction between colourless AgSbF6 and sky-blue Ag(SbF6)2 (molar ratio 2:1) in gaseous HF at 323 K yields green Ag3(SbF6)4, a new mixed-valence ternary fluoride of silver. Unlike in all other Ag(i)/Ag(ii) systems known to date, the Ag+ and Ag2+ cations are randomly distributed on a single 12b Wyckoff position at the 4ˉ axis of the I4ˉ3d cell. Each silver forms four short (4 × 2.316(7) ?) and four long (4 × 2.764(6) ?) contacts with the neighbouring fluorine atoms. The valence bond sum analysis suggests that such coordination would correspond to a severely overbonded Ag(i) and strongly underbonded Ag(ii). Thorough inspection of thermal ellipsoids of the fluorine atoms closest to Ag centres reveals their unusual shape, indicating that silver atoms must in fact have different local coordination spheres; this is not immediately apparent from the crystal structure due to static disorder of fluorine atoms. The Ag K-edge XANES analysis confirmed that the average oxidation state of silver is indeed close to +1 1/3. The optical absorption spectra lack features typical of a metal thus pointing out to the semiconducting nature of Ag3(SbF6)4. Ag3(SbF6)4 is magnetically diluted and paramagnetic (μeff = 1.9 μB) down to 20 K with a very weak temperature independent paramagnetism. Below 20 K weak antiferromagnetism is observed (Θ = -4.1 K). Replacement of Ag(i) with potassium gives K(i)2Ag(ii)(SbF6)4 which is isostructural to Ag(i)2Ag(ii)(SbF6)4. Ag3(SbF6)4 is a genuine mixed-valence Ag(i)/Ag(ii) compound, i.e. Robin and Day Class I system (localized valences), despite Ag(i) and Ag(ii) adopting the same crystallographic position.
