STRUCTURAL CHANGES IN THE δ-PHASE OF THE ALUMINIUM-NICKEL SYSTEM

The Al-Ni system has been the subject of numerous investigations. The β-phase in this system is well known for its being a defect lattice. In the Al-rich side of the stoichiometric composition AlNi, on the natural supposition that Al replaces Ni atom by atom, the addition of Al should produce a progressive increase in the lattice parameter and diminish the density. Contrary to expectation, the lattice parameter falls extremely rapidly, and the density falls well below that calculated on the basis of two atoms per unit cell as in the CsCl type structure. This remarkable fact, first discovered by Bradley and Taylor, is explained on the ground that the increase of Al content is really effected by