Calorimetric studies of LaM2NiMnO5 (M—Li, Na, K) nickelite-manganite heat capacity within the temperature range of 298.15–673 K

By means of the calorimetric method, we investigate the LaM 2 NiMnO 5 (M—Li, Na, K) nickelitemanganite heat capacities within the range of 298.15–673 K. For the studied compounds, within the stated temperature range, we reveal the λ-like effects respective to the second kind phase transition at 323 and 498 K for compounds containing Li, 323 K and 523 K for compounds containing Na, and 448 K for those containing K. Taking into consideration the phase transition temperatures, we derive the equations of the temperature dependence of the compound heat capacity. On the basis of the experimental values of the heat capacities as well as of the calculation data on the nickelite-manganite standard entropy, we calculate the temperature dependences of the heat capacity, the entropy, the enthalpy, and the reduced thermodynamic potential.