A new family of lithium rare-earth oxyborates, LiLn6O5(BO3)3 (Ln = Pr-Tm):: Crystal structure of the gadolinium phase LiGd6O5(BO3)3

A new family of lithium rare earth oxyborates of formula LiLn(6)O(5)(BO3)(3) (Ln = Pr-Tm) has been discovered in the ternary-phase diagrams Li2O-Ln(2)O(3)-B2O3. Single crystals of LiGd6O5(BO3)(3) were grown by the flux method. The structure of the oxyborate was solved using a data collection with a four-circle automatic diffractometer (CAD-4) and with MoK alpha radiation. The cell is monoclinic (space group P2(1)/c, Z = 4) with a = 8.489(4) Angstrom, b = 15.706(3) Angstrom, c = 12.117(6) Angstrom, beta = 132.27(2)degrees, and V = 1195(1) Angstrom(3). Refinement of 198 parameters using 4402 independent reflections having intensity I > 3 sigma (1) led to R = 0.037 (wR = 0.087). The structure of LiGd6O5(BO3)(3) can be described as a three-dimensional framework, (Gd6O14)(10-), of Gd polyhedra connected by common edges and corners, forming cavities where Li and B atoms are inserted. Some oxygen atoms share only Gd polyhedra, justifying the oxyborate label. (C) 1999 Academic Press.