ON THE PREPARATION OF SINGLE-CRYSTALS OF 11CAO-CENTER-DOT-7AL(2)O(3)CENTER-DOT-CAF2 AND THE CONFIRMATION OF ITS CRYSTAL-STRUCTURE

Single crystals of 11CaO . 7Al(2)O(3) . CaF2(C(11)A(7) . CaF2) of 40-1 20 mu m in size were prepared by a flux evaporation method. The crysta ls were colorless trigonal tristetrahedrons with a refractive index of 1.601. By the method of single crystal X-ray diffraction it has been confirmed that the C(11)A(7) . CaF2 is cubic, with a = 11.981 Angstrom , space group <I(4)over bar 3d>, Z = 2 and D-X = 2.720 g cm(-3) The ca lcium atom is coordinated either to six oxygen atoms in an irregular [ CaO6] coordination with 2.380 Angstrom, 2.401 Angstrom and 2.502 Angst rom for Ca-O distances or to six oxygen atoms and one fluorine atom in an asymmetric arrangement with 2.816 Angstrom for F-Ca distance. The aluminum atoms are coordinated to four oxygen atoms forming two differ ent AlO4 tetrahedra: (1) the [Al(1)O(2)(4)], with symmetry (4) over ba r and Al(1)-O(2) distance 1.745 Angstrom; and (2) the [Al(2)O-4] compo sed of one Al(2) atom, one O(1) atom and three O(2) atoms, with symmet ry 3, Al(2)-O(1) distance = 1.740 Angstrom and Al(2)-O(2) distance = 1 .757 Angstrom. Neighboring AlO4 tetrahedra are connected with each oth er by sharing oxygen atoms resulting in a three dimensional [AlO4] net work-the basic framework of the crystal structure of C(11)A(7) . CaF2. (C) 1997 Elsevier Science Ltd.