Thermodynamics of oxygen in CaMnO3 − δ

Abstract

The experimental data for equilibrium oxygen content were used in order to extract increments of partial molar thermodynamic functions of oxygen with changes of oxygen stoichiometry in calcium manganite CaMnO 3−δ . It is shown that along with the oxygen exchange reaction, thermal excitation of Mn 4+ cations plays an important role in equilibration of charged manganese species that appear in response to the loss of oxygen at heating. The interrelation of partial molar enthalpy and entropy of oxygen with electron and ion defect formation parameters is obtained in approximation of the point defect model. The nearly linear changes of oxygen partial molar enthalpy are shown to directly reflect thermally driven changes in concentration of Mn 3+ cations.

Impact of the Sr content on the redox thermodynamics and kinetics of Ca1−xSrxMnO3−δ for tailored properties

“…The enthalpy Δ h ° of CaMnO 3− δ is ≈20 kJ mol −1 and its thermal entropy is ≈20 J K mol −1 higher compared to earlier results, 31,32 but are comparable to results by Goldyreva et al 33 Moreover, the results of Ca 0.95 Sr 0.05 MnO 3− δ , 21 Ca 0.9 Sr 0.1 MnO 3− δ 21 and Ca 0.6 Sr 0.4 MnO 3− δ 34 are comparable as well. Thus, we conclude, that the discrepancies are due to experimental differences.…”

The favourable thermodynamic properties of Fe-doped CaMnO3 for thermochemical heat storage

“…In the low d orthorhombic phases, the enthalpies of CM and CMF91 are quite different from one another, and in the case of CMF91 the enthalpy shows a strong dependence of d. For d excess $ 0.08, within the cubic regime, the , respectively, in the cubic and orthorhombic regimes. 38 The heat storage capacity per unit mass of perovskite (Q M (kJ kg ABO 3 À1 )), determined according to the eqn (3), is presented in Fig. 12b as a function of d f (a), where the d i values are xed at 0.01, 0.05, and 0.18, respectively, for CM, CMF91 and CMF73.…”

Measuring Thermochemical Energy Storage Capacity with Redox Cycles of Doped-CaMnO3

“…Undoped CaMnO3-δ has excellent reducibility at these conditions but undergoes effectively irreversible phase transitions at high-T reduction (17,18). To stabilize CaMnO3-δ for reduction in chemical looping combustion applications, many have focused on B-(i.e., Mn-) site doping with compositions like CaMeyMn1-yO3-δ family, where Me is an earth-abundant cation such as Fe, Ti, or Mg (19)(20)(21).…”