PHASES AND TWINNING IN C2AL3B48 (BETA ALB12).
Technical rept. no. 2
CARBORUNDUM CO NIAGARA FALLS N Y
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The aluminum-boron phase described as beta-AlB12 was shown to consist of two crystallographically related, intergrown phases with the bulk stoichiometry of C2Al3B48. One phase A was orthorhombic with a 12.34A, b 12.631A and c 5.08A and space group Cmma or C2ma. The other phase B was also orthorhombic with a 6.17, b 12.631 and c 10.161 and space group Ammm, A222 or A2mm. Twinning was always present and occurred across both 110 faces. Occasionally, an unusual type of twinning appeared in which the a and b axes of both phases were parallel. This was interpreted as evidence of a disproportionation from a single high temperature phase. This was verified experimentally. The high temperature phase C was tetragonal with a 8.82A, b 5.09A and space group P4nmm, P4n or P4 sub 2n. The transformation which is reversible was gradual and complete at about 850C. Author