Defect equilibrium in PrBaCo2O5 at elevated temperatures

Abstract

a b s t r a c t A defect equilibrium model for PrBaCo 2 O 5+δ is suggested based on oxygen non-stoichiometry data. The model includes reactions of oxygen exchange and charge disproportionation of Co 3+ cations. The respective equilibrium constants, enthalpies and entropies for the reactions entering the model are obtained from the fitting of the experimental data for oxygen non-stoichiometry. The enthalpies of oxidation Co 2+ -Co 3+ and Co 3+ -Co 4+ are found to be equal to 115 7 9 kJ mol -1 and 45 74 kJ mol -1 , respectively. The obtained equilibrium constants were used in order to calculate variations in concentration of cobalt species with non-stoichiometry, temperature and oxygen pressure.

Correlating High-Temperature Defect and Magnetic Structures with Anomalous Chemical Expansion in an Outstanding PrBa0.5Sr0.5Co1.5Fe0.5O6−δ Positrode

“…As can be seen, the obtained σ values tend to decline at reducing P Od 2 and increasing temperature, which is typical for layered double perovskites. 42,66 Also, the respective σ = f(P Od 2 ) isotherm measured at 973 K in this work is in agreement with previously published data. 27 One can acknowledge a very high overall level of PBSCF conductivity, achieving ∼500 S/cm at ∼1000 K in an air atmosphere, which suggests negligible contribution from electron transport in electrode losses for this material.…”

“…The temperature of each calculated isotherm is additionally marked. As can be seen, the obtained σ values tend to decline at reducing P Od 2 and increasing temperature, which is typical for layered double perovskites 42,66. Also, the respective σ = f(P Od 2 ) isotherm measured at 973 K in this work is in agreement with previously published data 27.…”

“…Interestingly, the preliminarily measured temperature dependence of PBSCF conductivity in air is in some contradiction with the earlier reported data at T < 700 K but agrees well at higher T values,27,29 see FigureS5in the Supporting file. One should note however that similar inconsistencies are typical for other layered cobaltites, especially when studied by different authors 46,67,68. Still, at a semiquantitative level, the data obtained in this work supports earlier findings: PBSCF conductivity increases at cooling and becomes constant at ∼600 K. Also, the measured Seebeck coefficient supports the highly conductive nature of the studied compound, being less than 50 μV/K even at 1223 K, FigureS5in the Supporting Information.…”

Relating defect chemistry and electronic transport in the double perovskite Ba1−xGd0.8La0.2+xCo2O6−δ (BGLC)

“…represents an average cobalt valence state of Co to 45 kJ mol -1 , close to values for cobalt double perovskites in the literature. 13,14,[16][17][18] For cobalt disproportionation (Eq. 5), the entropy change is expectedly small (-10 to -30 J mol -1 K -1) , as no gas molecules are formed or consumed in the reaction.…”

“…Several approaches have been undertaken to describe the defect chemistry of BaLnCo2O6-δ double perovskites, using a simple LnCoO3 perovskite as the reference structure with the introduction of 50% Ba on lanthanide site as an acceptor dopant. [12][13][14][15][16][17][18] The ordered oxygen vacancies are then further described by an association reaction between the lanthanide cation and the vacancy. This approach has been shown to accurately predict the oxygen nonstoichiometry in PrBaCo2O6-δ (PBCO) and GdBaCo2O6-δ (GBCO) at high temperatures.…”