C. Pagnoux

The synthesis and crystal structures of novel antimony compounds: A4Sb4O8(X4O12) (A:K, Rb, Cs, Tl; X =Si, Ge)

Abstract A series of A 4 Sb 4 O 8 ( X 4 O 12 ) compounds ( A =K, Rb, Cs, Tl; X =Si, Ge) have been prepared either by solid-state reaction or via a sol-gel route. Single crystals of the cesium compounds have been isolated and their structure determined by X-ray diffraction. Cs 4 Sb 4 O 8 (Si 4 O 12 ) crystallizes in the tetragonal system, space group P 4 2 / mmc with a = 7.172(1)A, c = 19.645(2)A, Z = 2. The structure was determined from 557 reflections collected on a Nonius CAD4 diffractometer using the Mo Kα radiation. The final R index and weighted R w index are 0.026 and 0.024, respectively. The structure is built up from planes of cross-linked chains of corner-sharing SbO 6 octahedra, linked together via corner-sharing by four-membered Si 4 O 12 single rings. This three-dimensional arrangement delimits intercrossing tunnels wherein Cs cations are situated. Cs 4 Sb 4 O 8 (Ge 4 O 12 ) crystallizes in the tetragonal system, space group I 4 1 22 with a = 10.241(1) A, c = 40.073(6)A, Z = 8. Its structure was determined from 1303 reflections and refined to R = 0.034 and R w = 0.035. It appears as a slightly distorted form of the silicate analogue.

Sintering of solid solution compositions K(Ti1−xSbx)O(P1−xSix)O4 prepared via sol-gel or mechanochemical mixing

Abstract Preparation of dense pellets of solid solution compositions K(Ti 1−x Sb x )O(P 1−x Si x )O 4 has been studied. Two main routes have been investigated: mechanochemical mixing and sol-gel. For both methods, preparation conditions have been optimized by studying the influence of various parameters such as: heating rate, calcination temperature, cooling rate and sintering treatment. This study shows mainly that the calcination temperature must be choosen at the onset of the crystallization process and that a sintering treatment at 1323 K for 15 hr leads to the best results.

Alkali antimony silicates as precursors to new inorganic acids

Abstract Two alkali antimony silicates, K 4 Sb 4 O 8 (Si 4 O 12 ) and Cs 3 Sb 3 O 6 (Si 2 O 7 ) with strongly covalent and rather open octa hedraltetrahedral frameworks have been ion exchanged in acidic medium. Their proton exchanged derivatives are hydrated and their water content has been studied at 20°C as a function of relative humidity. Both compounds are true lattice hydrates and their thermal behavior, studied with use of TGA and X-ray diffraction, indicates that their dehydration process is reversible up to about 400°C. Titrations with different alkali hydroxide solutions show that they behave as solid acids with ion exchange properties.