Single-Crystal Growth and Structure Determination of a New Oxide Apatite, NaLa₉(GeO₄)₆O₂

NaLa₉Ge₆O₂₆, hexagonal,a=0.9883(2) nm,c=0.7267(3) nm,V=6.147(3)×10⁵nm³, space groupP6₃/m,Z=1,D_calc= 5.739 g cm^-3,λ(MoKα)=0.071069 nm,μ=225.16 cm^-1,F(000)=924,T=298 K,R=0.031,R_w=0.037 for 966 measured unique reflections. Single crystals of NaLa₉Ge₆O₂₆were grown both by a high-temperature flux method and from a melt system. The crystal structure was found to be similar to that of the silicate oxyapatite NaY₉Si₆O₂₆. The 4fcation sites are occupied disorderedly by La and Na. On the other hand, the 6hcation sites are occupied by La only. This compound constitutes a new member of the oxyapatite-type structure family with general formulaA_xLn_10-xB₆O₂₄O _3-x(x=1,A=alkali metals,B=Si, Ge,Ln=rare earth).