Single-crystal growth and structure determination of a new oxide apatite, NaLa9(GeO4)6O2

NaLa9Ge6O26, hexagonal, a = 0.9853(2) nm, c = 0.7267(3) nm, V = 6.147(3) x 10(5) nm(3), space group P6(3)/m, Z = 1, D-calc = 5.739 g cm(-3), lambda(MoK alpha) = 0.071069 nm, mu = 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 NaLa9Ge6O26 were 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 4f cation sites are occupied disorderedly by La and Na. On the other hand, the 6h cation sites are occupied by La only. This compound constitutes a new member of the oxyapatite-type structure family with general formula A(x) Ln(10-x)B(6)O(24)O(3-x) (x = 1, A = alkali metals, B = Si, Ge, Ln = rare earth). (C) 1998 Academic Press.