Role of Aluminum Ion in the Structure of Alkaline Earth Aluminoborate Glasses

The composition dependence of some physical properties of Cabal and Babal glasses is discussed for the purpose of elucidating the role of aluminum ion in the structure of alkaline earth aluminoborate glasses. To interpret the experimental results on the basis of the glass structure, three rules are assumed about interlinking relation among AlO4 tetrahedron, BO4 tetrahedron and BO3 triangle as follows. (Rule 1) In the structure of alkaline earth aluminoborate glass, when each content of MO and B2O3 in the glass exceeds a definite value, preferential interlinking between AlO4 and BO4 groups is made into the formation of a tetrahedron couple comprising those two kinds of tetrahedral group. (Rule 2) The interlinked tetrahedron couple is impossible to exist only by itself, but is forced to link to BO3 triangles at its six corners in any case. Hence, the formation of AlB3O7