Redox Thermochemistry, Thermodynamics, and Solar Energy Conversion and Storage Capability of Some Double Perovskite Cobaltites

Abstract

The oxygen nonstoichiometry, δ, and oxidation enthalpy, ΔH ox , of double perovskites RBaCo 2 O 6−δ (R = Sm or Eu) were simultaneously measured depending on the temperature and oxygen partial pressure, p O 2 . Theoretical equations for ΔH ox (T, δ) and p O 2 (T, δ) were derived from the defect structure model based on the oxygen exchange and cobalt disproportionation reactions. These equations were fitted independently to each of the experimental ΔH ox (T, δ) and p O 2 (T, δ) data sets. The resulting enthalpies of defect reactions were found to be almost the same irrespective of the calculation method. In other words, the models, describing satisfactorily the data, can be used to calculate both compositional dependences and redox thermodynamics of RBaCo 2 O 6−δ (R = Sm or Eu). In addition, from the previously published data and the data presented here, trends were determined in the defect reaction thermodynamics of RBaCo 2 O 6−δ (R = La, Pr, Nd, Sm, Eu, Gd, or Y). Drop calorimetric measurements were performed in air to obtain enthalpy increments for RBaCo 2 O 6−δ (R = Sm or Eu) with variable oxygen content because the samples lost oxygen upon being heated in the calorimetric cell. As-obtained data were used to calculate the functional dependences of enthalpy increments of EuBaCo 2 O 5.56 and SmBaCo 2 O 5.6 with a constant oxygen content. In addition, as an example of practical application-oriented calculations for solar energy conversion and oxygen storage, the performances at equilibrium of RBaCo 2 O 6−δ (R = Pr, Sm, Eu, or Gd) were evaluated and compared to those of SrFeO 3−δ as a reference material.

Defect-Induced Properties and Thermodynamics of La0.5Ba0.5CoO3–δ

“…so as to take into account the preferential oxygen vacancy formation within the rare-earth layers. In the recent study, 29 we investigated the trends in defect reaction enthalpies for RBaCo 2 O 6-δ (R = rare-earth ion), which allowed us to conclude that ∆ ○ H of pseudocluster formation,…”

Thermodynamics of Formation and Disordering of YBaCo2O6-δ Double Perovskite as a Base for Novel Dense Ceramic Membrane Materials

“…In contrast with the double perovskite cobaltites RE BaCo 2 O 6-δ ( RE = La, Pr, Nd, Sm, Eu) with larger rare-earth ions, both YBC and GBC are characterized by somewhat lower cobalt disproportionation enthalpy of around 20 kJ∙mol −1 (as compared with ≈35 kJ∙mol −1 for RE BaCo 2 O 6-δ ). In addition, YBC and GBC possess significantly lower enthalpy of oxygen vacancy localization in the rare-earth layers of the double perovskite structure, around −100 kJ∙mol −1 against ≈−50 kJ∙mol −1 for RE BaCo 2 O 6-δ [ 13 , 27 ]. The strongly negative values of the localization enthalpy fitted for YBC are in line with the trend revealed recently in [ 27 ] which shows increasing preference for localization in the rare-earth layers with decreasing radius of the rare-earth cation.…”

“…In addition, YBC and GBC possess significantly lower enthalpy of oxygen vacancy localization in the rare-earth layers of the double perovskite structure, around −100 kJ∙mol −1 against ≈−50 kJ∙mol −1 for RE BaCo 2 O 6-δ [ 13 , 27 ]. The strongly negative values of the localization enthalpy fitted for YBC are in line with the trend revealed recently in [ 27 ] which shows increasing preference for localization in the rare-earth layers with decreasing radius of the rare-earth cation. We should emphasize here that the corresponding reaction 2 in Table 2 is not a process of the real defect cluster formation, but rather a way of accounting for the experimentally ascertained fact that in the A-site ordered layered double perovskite cobaltites the oxygen vacancies tend to locate in the rare-earth layers.…”

“…Most of the previous studies of RE BaCo 2 O 6-δ concerned their crystal structure [ 16 , 17 , 18 ], magnetic [ 17 , 19 , 20 ] and transport [ 21 , 22 ] properties, while their oxygen content, defect structure and thermodynamic properties were investigated primarily at high temperatures [ 15 , 23 , 24 , 25 , 26 ], with only a few recent works focused on the intermediate-temperature range [ 13 , 15 , 27 , 28 ]. In this respect, the object of this work, YBC, is no exception.…”

Layered Oxygen-Deficient Double Perovskites as Promising Cathode Materials for Solid Oxide Fuel Cells

“…Although this work overviews the last trends in LODPs, a number of recent publications fell within the reviewing procedure. In our opinion, these works [ 205 , 206 , 207 , 208 , 209 , 210 , 211 ] should be mentioned with no detailed analysis.…”