Stabilization of high temperature tysonite type compounds in the Sr-Yb-F system-synthesis and Rietveld refinement

Several compositions of the type SrxYb1-xF3-x (x = 0.20, 0.25, 0.30. 0.33) were prepared by heating the well ground mixtures of appropriate amounts of SrF2 and YbF3 at 1100°C. The substitution of Yb3+ in YbF3 by Sr2+ for x = 0.25 and 0.3 leads to new single phasic fluorides with tysonite type structure. Quenching was shown to be essential to stabilize these phases. The XRD pattern of Sr0.25Yb0.75F2.75, i.e., SrYb3F11 was fitted on a hexagonal unit cell with space group P63/mmc with a = 3.9606(4) and c = 6.9731(5) Å. According to Rietveld refinements the as prepared SrYb3F11 crystallizes in the disordered HT-form of the tysonite type structure. The magnetic measurements of Sr0.25Yb0.75F2.75 show paramagnetic behaviour with a magnetic moment of 4.6 μB which corresponds to the f13 configuration of Yb3+.