The heat capacities and thermodynamic properties of NiAl2O4 and CoAl2O4 measured by adiabatic calorimetry from T = (4 to 400) K

The low-temperature heat capacity of NiAl2O4 and CoAl2O4 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 NiAl2O4 and at T = 9 K for CoAl2O4. The exact cause of these anomalies is unknown. From our results, we suggest a standard entropy for NiAl2O4 at T = 298.15 K of (97.1 ± 0.2) J · mol−1 · K−1 and for CoAl2O4 of (100.3 ± 0.2) J · mol−1 · K−1.