Crystallography of the Aluminum Borides

Abstract

At present, there are five authenticated phases in the aluminum—boron system:

• 1. AlB2—hexagonal; bronze-colored, thin platelets.

• 2. AlB10—orthorhombic; black lustrous, pyramidal and tabular; new phase.

• 3. α-AlB12 —tetragonal, pseudocubic; hematite-like plates and laths (irregular pseudooctahedra) ; thin sections orange-red in strong transmitted light.

• 4. β-AlB12—orthorhombic, pseudotetragonal; amber-colored, bipyramidal; poly synthetically twinned on (110) and (110).

• 5. γ -AlB12—orthorhombic, polytypically related to α -AlB12; hematite-like, orthogonal laths; new phase.

(1) is the only aluminum boride phase whose properties are different from those of boron and also the only phase whose structure is known. (3), (4), and (5) have common unit cell vectors which show that, as in boron carbide and the known forms of boron, boron icosahedra represent the major structural elements.