Experimental Study of the Variation of the Degree of Order with Temperature in a Copper-Palladium Alloy

The paper gives an account of an x-ray study of the copper-palladium alloy Cu 3 Pd, with special reference to the variation of the degree of order with temperature as revealed by the degree of tetragonality of the structure at different temperatures. From the relation between the axial ratio of the structure and the temperature it is concluded that the transformation from the cubic face-centred structure to the tetragonal face-centred structure takes place at 460°c and the material is fully ordered at temperatures below about 270°c when the axial ratio c/a is 0.9851 and the a -parameter 3.7021 kx at 18°c. On the assumption that the degree of tetragonality gives a measure of the degree of order it is concluded that the relation between the axial ratio and the degree of order is given by c/a =1 - 0.015 W when W is the degree of order.