Heat capacity and thermodynamic functions of new cobaltic manganites NdM2IICoMnO6 (MII is Mg, Ca, Sr, or Ba) Within the temperature range of 298.15–673 K

Resumo

The results of thermodynamic studies of the cobaltic manganites NdM₂^IICoMnO₆ (M^II is Mg, Ca, Sr, or Ba) are presented. In the calorimetric studies of the heat capacity within the range of 298.15–673 K, a second kind λ-shaped phase transitions in the C_p(T) dependences was discovered: at the temperatures of 373 and 523 K for NdMg₂CoMnO₆; at 348 and 498 K for NdCa₂CoMnO₆; at 423 and 548 K for NdSr₂CoMnO₆; and at 323 and 498 K for NdBa₂CoMnO₆. We derive the equations for the temperature dependence of the heat capacity with account for these phase transitions. We calculate the temperature dependences of the thermodynamic functions: entropy, S⁰(T), enthalpy, H⁰(T)–H⁰(298.15), and the reduced thermodynamic potential, Φ^xx(T), of the studied manganites.