CRYSTAL STRUCTURE OF A NEW OXYBORATE OF LITHIUM AND GADOLINIUM OF FORMULA LiGd₆O₅(BO₃)₃

J.P.Chaminade,V. Jubera, P.Gravereau and C. Fouassier

Institut de Chimie de la Matiere Condensée de Bordeaux (ICMCB-CNRS) [UPR 9048], Université de Bordeaux I, Avenue du Dr Albert Schweitzer, 33608 Pessac Cedex (France)

Search of new scintillators attracts the scientific community owing to their wide range of applications. Recently some of us have demonstrated the interest of Li₆ M_1-x Ce_x (BO₃)₃ (M=Gd,Y) as neutrons detectors. The study of the Li₂O- Gd₂O₃- B₂O₃ ternary phase diagram led us to discover a new composition LiGd₆B₃O₁₄. Single crystals have been grown in the Li-Gd-B-O system using Li₂O- B₂O₃ rich melt. The aim of this work is the structural determination of this new compound.

The structure of the oxyborate LiGd₆O₅(BO₃)₃ was solved using a data collection with an Enraf-Nonius four circles automatic diffractometer (CAD-4) and with MoKa radiation. The cell is monoclinic (space group P2₁/c, Z=4) with a= 8.479(4) A, b= 15.706( 3) A, c=12.117( 6) A, b= 132.27(2) °, V=1195 (1) A³ . Refinement has been made with SHELX -93 program from 4452 independent reflections having intensity (I > 3(I)) , 218 variables parameters and lead to R=0.0392 (wR= 0.0981)).

The structure of LiGd₆O₅(BO₃)₃ can be described as made up of three series of BO₃ isolated triangles , with six independent Gd atoms in six and seven coordination, and Li atoms in a distorted tetrahedra.The particular feature of this structure is related to the different cationic environment of oxygen atoms : five oxygen atoms share only four Gd atoms, three other O are linked to two Gd and one B atoms, two O atoms to three Gd and one B atoms and finally the last four O atoms are connected to two Gd,one B and one Li atoms.