Specific heat capacities of alloys of the non-stoichiometric GaNi 3‘x phase

The heat capacities of three alloys, Ga0.24Ni0.76, Ga0.25Ni0.75, and Ga0.27Ni0.73, within the homogeneity range of the nonstoichiometric compound GaNi 3‘x were determined between 423 and 1273 K. Two different methods, flat specimen DSC (423-1073 K) and drop calorimetry (773-1273) were used and the overlap of the results was satisfying for all three compounds. Cp-values start at about 26-27 kJ mol-1 K-1 (423 K), increase slightly up to 800-900 K and rise strongly at higher temperatures. This behavior is not unusual for metals. Up to about 900 K the Neumann-Kopp rule is suitable to estimate the Cp-values. The only significant difference between the three alloys is the weaker rise of C p for Ga0.27Ni0.73 in comparison to Ga 0.24Ni0.76 and Ga0.25Ni0.75. The Cp-values at 1273 K are about 35 kJ mol-1 K-1 for Ga0.27Ni0.73 and close to 40 kJ mol-1 K-1 for the other two alloys. The experimental values could be fitted by the least squares method using the polynomial Cp = a + b.T + c.T2. The widely used T-2-term was not applied because it caused an unsatisfying approximation to our experimental values at lower temperature (423-600 K). This can be explained by the lack of experimental values at room temperature and slightly above. The extrapolated C p-values at room temperature, Cp(298), are close to 25 kJ mol-1 K-1 for all three compounds. Œ 2003 Elsevier Ltd. All rights reserved.