Ordered Alloys in the Cobalt-Palladium System

Ordered phases in the Co-Pd alloy system are studied by electron diffraction, using evaporated single crystal films of the alloys with Pd content extending from 20 to 100 at.%. Two types of the ordered states are found in this system; one is the Ll 2 type (Cu 3 Au type) and exists over the range of composition of Pd between 60 and 90 at.%. The temperature of order-disorder transition is 830°C for the 80 at.% Pd alloy. The other has the structure of Ll 0 type (CuAuI type) and exists within a narrow region of composition around CoPd. This phase is accompanied by two-phase regions over fairly wide ranges at both sides of it. The transition temperature is estimated to be higher than 850°C.