Effect of Heat Treatment on the Specific Heat of Cu-40-at.% Ni below 3°K

Abstract

Assuming that clusters contribute to the specific heat as an Einstein term (represented by a Thirring expansion), it is found that (a) the magnitude of the cluster term (proportional to the number of clusters) is independent of quenching temperature for quenching temperatures above about 550°C and nearly doubles for some lower quenching temperatures, and (b) the electronic-specific-heat coefficient shows a strong dependence on the magnitude of the cluster term and the Debye temperature a weak dependence. The first observation (a) may be interpreted as showing (i) that cluster formation only occurs at temperatures below about 550°C, (ii) that cluster formation during quenches from higher temperatures occurs because an excess of thermally generated lattice vacancies is then present which facilitiates atomic movement, (iii) either the number of excess vacancies available is independent of quenching temperature (owing, for example, to aggregation effects) or cluster formation during quench is limited by the distance of atomic movement required, and (iv) it is impossible to inhibit cluster formation in a sample of the size used (50 g) with the present quenching techniques. The second observation (b) suggests a way of extrapolating to the unclustered state. It may also indicate that the Einstein term is not the best representation for the cluster specific heat.