Oxygen non-stoichiometry and defect equlibria in CaMnO3 − δ

Abstract

A defect equilibrium model is suggested for CaMnO 3−δ based on oxygen non-stoichiometry and conductivity data. The model includes reactions of oxygen exchange and thermal excitation of electrons. The respective equilibrium constants, enthalpies and entropies for the reactions entering the model are obtained from the fitting of the calculated and experimental data for oxygen nonstoichiometry. The energy parameters obtained from the model and variations in the concentration of manganese species enable explanation of temperature and oxygen pressure dependencies of thermopower and conductivity within frameworks of a small polaron type model.

Examination of Perovskite Structure CaMnO3-δwith MgO Addition as Oxygen Carrier for Chemical Looping with Oxygen Uncoupling Using Methane and Syngas

“…Despite this fact, the amount of oxygen that is available for CLOU depends on the difference between the oxidized and reduced form of CaMnO 3-. Though oxidized CaMnO 3-has less oxygen at higher temperature, it may be reduced further at low partial pressures of O 2 , as would be existing in the fuel reactor of a chemical-looping unit [31,41]. For instance, for an oxygen partial pressure change, from 0.05 atm to 0.005 atm, the oxygen carrier CaMnO 3-should release approximately the same amount of oxygen at higher and lower temperature cases employed in this work.…”

“…Leonidova et al [31] and Goldyreva et al [41] studied the oxygen deficiency under different conditions and provided a phase diagram of CaMnO 3-where was a function of oxygen partial pressure at different temperatures. At a fixed temperature, increases with decreasing oxygen partial pressure meaning that more oxygen is released under lower oxygen partial pressure environment.…”

Electron transport in CaMnO3 − δ at elevated temperatures: a mobility analysis

“…The temperature variations of parameters n and g can be calculated from (3) and (4) with the use of ΔS°and ΔH°obtained elsewhere [30]. The results for δ = 0.02 and 0.07 are shown in Fig.…”

“…Before discussing mobility and conduction mechanism, we need in the first place to understand how concentration of electrons, i.e., of Mn 3+ cations, changes with temperature. It can be shown [30] , respectively, and oxygen non-stoichiometry are interrelated as…”

Thermodynamics of oxygen in CaMnO3 − δ

“…is taken into account [18]. This reaction gives rise to some amount of Mn 5+ cations in СаMnO 3−δ that depends on the ambient atmosphere.…”