Makoto Hirabayashi, Hideyo Maniwa and Seizo Nagasaki
In previous paper,we have reported many anomalous physical properties through the order-disorder transformation in Mg-Cd alloys of various compositions.
We performed more detailed measurements of temperature dependencies of specific heat and expansion coefficient of the alloys. The results of these experiments are as follows : (1) The transition temperature-composition curve is of aparabolic form, having two kinks at about 38 and 67 atom%Cd (Fig. 1). Th is observed curve does not agree with two calculated curves for face-centered cubic lattice, i.e. the one obtained by Shockley with the Bragg-Williams approximation and the other recently obtained by Li with the quasi-chemical method. (2) From measurements of specific heat from room temperature to above the transition temperature, we calculated the configurational energies and entropies of transformation. On both the configurational energy-composition curve and configurational entropy-composition curve,there are three maxima at the atomic ratios corresponding respectively to 3:1,1:1 and 1:3 (Fig. 3 and 4). (3) Two steps of changes are found in specific heat-temperature curves and expansion coefficent-temperature curves for the alloys containing from 38 to 67 atom%Cd, except a narrow range about 50 atom%Cd (Fig. 2). Such anomalies can not as yet been explained.
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