The crystal structure of ZrAl

Abstract

The crystal structure of the intermetallic phase ZrAl was determined from x-ray powder films of impure specimens. Several alloys were prepared by arc melting suitable quantities of the pure metals in argon to give a composition of 50 at.% for each component, but all the films showed the presence of considerable quantities of the neighboring phase Zr/sub 2/Al/sub 3/. According to the phase diagram for the zirconium--aluminum system, the stable composition range for ZrAl is ondy a few at.% and furthermore the alloy is unstable above 1250 deg C. It is apparent that the preparation of a pure specimen of ZrAl is difficult, and metallographic examination of the polished specimens showed the presence of two phases, Zr/sub 2/Al/sub 3/ and ZrAl. The sharply defined lines belonging to the Zr/sub 2/Al/sub 3/, whose structure is now known, were rejected. Apart from a few unidertified lines, the remaining lines were indexed on the basis of an orthorhombic unit cell of dimensions similar to that given by Edshammar for HfAl; the dimensions found were a = 3.359 plus or minus 0.001, b = 10.887 plus or minus 0.003, and c =4.274 plus or minus 0.001 A. (N.W.R.)