Search

A series of mixed crystals with general formula Ba7−xNayF12Cl2−zBrzin the ordered modification (space group P‐6) has been studied by single crystal x‐ray diffraction. Depending on synthesis conditions, the disorder in the channels (i.e. occupation of 0 0 z sites) can be changed. The disorder is found to be correlated with the refined Na content, and its effect on Ba‐Cl(Br) bond length is discussed.

The new fluoride BaSr(NH4)Mg5F15precipitates as a nanocrystalline powder from aqueous solutions of the alkaline earth ions and ammonium fluoride. The compound crystallizes in the tetragonal tungsten bronze structure type with lattice parameters of a,b= 12.4492(14) Å and c= 3.9421(4) Å (space group P4/mbm[Nr. 127], structure refinement from powder data, RBragg= 4.0 %). Corner‐linked magnesium‐fluoride octahedra form a channel structure which contains one empty triangular channel, one channel filled with Sr2+[CN = 8+4] and one channel with disordered Ba2+and NH4+(ratio 1:1) with CN = 7+8. Solid solutions between the composition limits Ba(Ba0.8Sr0.2)(NH4)Mg5F15and (Ba0.6Sr0.4)Sr(NH4)Mg5F15were obtained. The crystallite size increases from 15 to 75 nm with increasing barium concentration. The thermal stability between 350 to 450 °C depends on the amount of absorbed (NH4)F. Heated samples show luminescence and phosphorescence.

Crystals of the chemical composition Ba7F12Cl2were modified by adding a small amount of Ca2+to allow the synthesis of the corresponding bromine compound Ba[Ca]7F12Br2. These samples were prepared in a NaBr flux and characterized by single crystal x‐ray diffraction. The new structure crystallizes in a disordered arrangement in the hexagonal space group P63/m (176). The calcium ion has a coordination number of 6.

Crystals of ordered Ba6EuF12Cl2were found to form during high temperature flux growth. The structure was refined in the hexagonal space group P 6 to RF(R$^F_w$) = 0.024(0.024) for 326 reflections and 46 parameters. Lattice parameters are a= b= 1059.27(8) pm and c= 416.36(2) pm; Z = 1. The structure is isotypic to Ba7F12Cl2. No solid solution of Ba/Eu was observed, the Eu2+ions are located in the channels formed by 3 + 6 fluorine ions, occupying only one of the three metal sites of the Ba7F12Cl2structure.