The heat capacities and thermodynamic properties of NiAl 2O 4 and CoAl 2O 4 measured by adiabatic calorimetry from T = (4 to 400) K

Abstract

The low-temperature heat capacity of NiAl 2O 4 and CoAl 2O 4 was measured between T = (4 and 400) K and thermodynamic functions were derived from the results. The measured heat-capacity curves show sharp anomalies peaking at around T = 7.5 K for NiAl 2O 4 and at T = 9 K for CoAl 2O 4. The exact cause of these anomalies is unknown. From our results, we suggest a standard entropy for NiAl 2O 4 at T = 298.15 K of (97.1 ± 0.2) J · mol −1 · K −1 and for CoAl 2O 4 of (100.3 ± 0.2) J · mol −1 · K −1.