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 LiLn6O5(BO3)3 (Ln=Pr–Tm) has been discovered in the ternary-phase diagrams Li2O–Ln2O3–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 MoKα radiation. The cell is monoclinic (space group P21/c, Z=4) with a=8.489(4) Å, b=15.706(3) Å, c=12.117(6) Å, β=132.27(2)°, and V=1195(1) Å3. Refinement of 198 parameters using 4402 independent reflections having intensity I>3σ(I) 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.