Redox Materials Thermochemistry Data for Application in Concentrated Solar Power.
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We have measured thermodynamic data of perovskites ABOₓ with x=3-δ, i.e. ΔH and ΔS in dependence of the non-stoichiometry δ by means of thermogravimetric analysis. That means, we measured the mass changes in dependence of T and p(O₂), determined the corresponding non-stoichiometry changes and used this data to extract thermodynamic properties from van’t Hoff plots. In parallel, we performed density functional theory calculations (DFT) to get theoretical thermodynamic data.
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ExperimentalData | Retrieved via van't Hoff method from equilibrium thermogravimetric data. ΔH(Δδ) and ΔS(Δδ) determined (temperature dependence not considered), with Δδ = δ - δ₀; δ₀: δ at T = 400 °C, p|O₂ = 0.18 bar; δ₀: determined from entropy fit. Inaccurate values for δ₀ lead to a shift of the absolute δ values for some materials. This does not affect the accuracy of the relative oxygen release/uptake values. Experimental data may be highly inaccurate for extrapolated values (indicated by dashed lines). |
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TheoreticalData | ΔH(δ, T) calculated from DFT values for the reduction enthalpies from perovskite to brownmillerite, ΔS(δ, T) calculated as a sum of configurational and vibrational entropy and the partial molar entropy of oxygen. Vibrational entropy calculated from elastic tensors (from DFT, The Materials Project). If no elastic tensors are available, the data for SrFeO(3-δ) is used as an approximation. |