Synthesis, stability and zeolitic behavior of δ­ALn3F10,xH2O and γ­ThLn2F10,H2O phases (Ln = lanthanide)

Two series of hydrated fluorides have been prepared by a “chimie douce” process. For the first family, more than twenty five compounds of δ-ALn3F10,xH2O (A+ = alkaline ions, NH4+, H3O+ and Ln = lanthanide) have been prepared. They crystallize in the Fd [[3 with combining macron]] m space group (a ≈ 15.4 Å and Z = 16) and are isotypic with δ-(H3O)Yb3F10,xH2O (x = 1). The diamond-type structure of these phases (diamond stacking of octahedral units of antiprisms, called UOA[8]), creates cavities and tunnels where the water molecules can move. The second family, γ-ThLn2F10,H2O (Ln3+ = Er3+, Dy3+ and Yb3+) results from the substitution of Ln3+ and A+ by a tetravalent cation. The new compound γ-ThEr2F10,H2O (Fm [[3 with combining macron]] m space group, a = 10.739(1) Å and Z = 8) is isotypic with γ-KYb3F10. Water molecules are located inside the tunnels (8c sites) of a CCP stacking of UOA[8] through which they can move. For both series, the thermal stability and the zeolitic behaviour, studied by DTA/TGA and X-ray thermodiffractometry, are reported and a low zeolitic water capacity, around 2–4% in mass, is observed

Contribution Mössbauer à la recherche de l'ordre cationique dans les pyrochlores CsNiFeF6, CsLi0,5Fe1,5F 6 et CsLi0,5(Al, Fe)1.5F6

The analysis of EFGs and critical temperature range around T N, for the pyrochlore series CsLiIxNi II1-2xFeIII1+ xF6 and CsLiI0.5Fe III 1.5-yAlyF6, allows to predict cationic order in the following cases : undistorted CsNiFeF6 and CsLi0.5Fe 1.5F 6 (short range), distorted CsLi0.5(Al, Fe) 1.5F 6 (short and long range). Basically, the EFG occurs to be governed by the electric charge of the neighbouring cations. Various magnetic ordering temperatures have been measured.L'étude des gradients de champ électrique et de la largeur de la zone critique autour de TN, sur les pyrochlores mixtes CsLiI xNiII1-2xFe III 1+xF6 et CsLiI 0,5Fe III1,5-yAlIII yF 6, permet de prévoir l'existence d'un certain ordre cationique dans les cas suivants : systèmes non déformés CsNiFeF6 et CsLi 0,5Fe1,5F6 (ordres à courte distance) et système déformé CsLi0,5(AlyFe1,5- y)F6 (0 ≤ y ≤ 1, ordre à courte puis longue distance). Le gradient de champ électrique s'avère pour l'essentiel, déterminé par la charge des cations voisins. La température d'ordre magnétique varie notablement selon le composé