A review is given of phase analysis and structure studies on the Zr-Al and Hf-Al systems. The structures and properties of the phases are discussed and compared with those of some transition metal borides and silicides and other metal phases. The atomic parameters of Hf/sub 2/Al3 were refined.

The existence of various phases in the aluminumhafnium system was previously reported. Arc-melting followed by quenching to room temperature revealed phases having the composition Hf/sub 3/Al/sub 2/ and HfAl. Samples of compositions HfAl/sub 0.5-0.7/ gave weak lines similar to the oxygen-stabilized phase Zr/sub 5/Al/sub 3/O/sub x/. This suggested isomorphism between the Hf and Zr phases was confirmed by gradually adding oxygen (as HfO/sub 2/) to the samples. The unit cell of Hf/sub 3/Al/sub 2/ was found to be tetragonal with the dimensions a = 7.535 A and c = 6.906 A. The powder pattern of Hf/sub 5/Al/sub 3/O/ sub x/ could be indexed assuming a hexagonal unit cell with the dimensions a = 8.066 A and c = 5.678 A. The atomic positions and space groupings are given for each of the phases. (B.O.G.)