✍ Scribed by F. Kubel; M. Pantazi; H. Hagemann
No coin nor oath required. For personal study only.
Barium calcium magnesium fluoride (Ba 2 (Ba x Ca 1-x )Mg 4 F 14 , x=0.19-0.26) has been synthesized at 850 °C from precursors prepared by the solution precipitation method. Single crystals with composition of Ba 2.200(2) Ca 0.800(2) Mg 4 F 14 were obtained after prolonged heating. Lattice parameters from single crystal data are a = 12.4203( ) and c = 7.4365(5) Å [tetragonal, space group P4 2 /mnm (No. 136)]. They increase with increasing barium concentration within a given stability window. The structure is built of a network of MgF 6 octahedra forming a pyrochlore related channel system and isolated fluorine ions. Within the channels, heavy alkaline earth ions are located. The wide channel is filled with off-center positioned barium ions. The channel with a narrow cross section hosts both ions, Ca 2+ and Ba 2+ . The structure is isotypic with Pb 3 Nb 4 O 12 F 2 but has a different coordination around Ba/Ca and Pb, respectively. Doped with ~1% Eu(II), the compound shows intense blue luminescence under UV activation.
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