Heat capacity and thermodynamic functions of new cobaltic manganites NdM 2 II CoMnO6 (MII is Mg, Ca, Sr, or Ba) Within the temperature range of 298.15–673 K

Abstract

The results of thermodynamic studies of the cobaltic manganites NdM 2 II CoMnO6 (MII 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, S 0(T), enthalpy, H 0(T)–H 0(298.15), and the reduced thermodynamic potential, Φ xx (T), of the studied manganites.