On the preparation of single crystals of 11CaO · 7Al 2O 3 · CaF 2 and the confirmation of its crystal structure

Abstract

Single crystals of 11CaO · 7Al 2O 3 · CaF 2(C 11A 7 · CaF 2) of 40–120 μm in size were prepared by a flux evaporation method. The crystals 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 11A 7 · CaF 2 is cubic, with a = 11.981 Å, space group I4̄3d, Z = 2 and D X = 2.720 g cm −3. The calcium atom is coordinated either to six oxygen atoms in an irregular [CaO 6] coordination with 2.380Å, 2.401Å and 2.502Å for Ca-O distances or to six oxygen atoms and one fluorine atom in an asymmetric arrangement with 2.816Å for F-Ca distance. The aluminum atoms are coordinated to four oxygen atoms forming two different AlO 4 tetrahedra: (1) the [Al(1)O(2) 4], with symmetry 4̄ and Al(1)-O(2) distance = 1.745 Å; and (2) the [Al(2)O 4] composed of one Al(2) atom, one O(1) atom and three O(2) atoms, with symmetry 3, Al(2)-O(1) distance = 1.740Å and Al(2)-O(2) distance = 1.757Å. Neighboring AlO 4 tetrahedra are connected with each other by sharing oxygen atoms resulting in a three dimensional [AlO 4] network-the basic framework of the crystal structure of C 11A 7 · CaF 2.