Calorimetric Research into the Heat Capacity of Novel Nano-Sized Cobalt(Nickelite)-Cuprate-Manganites of LaBaMeIICuMnO6 (MeII = Co, Ni) and their Thermodynamic Properties

Abstract

The isobaric heat capacities of novel nano-sized cobalt-cuprate-manganite of lanthanum and barium LaBaCoCuMnO₆ and nickel-cuprate-manganite of lanthanum and barium LaBaNiCuMnO₆ were investigated by dynamic calorimetry over the temperature range of 298.15‒673 K. It is found that a λ-shaped effect is observed on the curve of the heat capacity dependence on temperature of LaBaCoCuMnO₆ at 523 K, while LaBaNiCuMnO₆ also has a similar effect at 473 K. Equations for the temperature dependence of the heat capacity of cobalt(nickelite)-cuprate-manganite of lanthanum and barium are derived with allowance for the temperatures of phase transitions. Based on the experimental data, the fundamental constants ‒ the standard heat capacities of the compounds under study were found. Irrespective of the experimental data, we also calculated the standard heat capacities of the mentioned compounds using the Debye theory using the characteristic temperatures of the elements, their melting points, the Koref and Nernst-Lindemann equations. The obtained calculated data on C⁰_p (298.15) of the compounds were in satisfactory agreement with the experimental data on the standard heat capacity. The standard entropies of LaBaCoCuMnO₆ and LaBaNiCuMnO₆ were calculated by the ion increment method. We calculated the temperature dependences of the enthalpy H^o(T)- H^o(298.15), entropy ΔS^o(T), and the reduced thermodynamic potential ΔФ**(Т).