Thermodynamics of formation of solid solutions between BaZrO3 and BaPrO3

A linear relationship between the standard enthalpy of formation from binary oxides, ΔfHox, and the Goldschmidt tolerance factor, t, for some AIIBIVO3 (A = Ca, Sr, Ba; B = Ti, Zr, Hf, Ce, Pr, Tb, U, Pu, Am) perovskite oxides was used for estimation of ΔfHox of Pr-substituted barium zirconates BaZr1–xPrxO3. A dependence of the relative change of the standard entropies, S298, on the relative change of the molar volumes in the reactions of formation of AIIBIVO3 (A = Ca, Sr, Ba; B = Ti, Zr, Hf, Ce) from binary oxides was also found to be linear. Using this dependence, a relatively precise method of estimating S298 was proposed, and S298 of BaPrO3 was calculated as (162.8 ± 2.8) J·mol-1·K-1. Knowing S298 of BaPrO3 and using the literature data for S298 of BaZrO3, the values of S298 of BaZr1–xPrxO3 were predicted on the assumption that BaZr1–xPrxO3 is a regular or ideal solution of BaPrO3 in BaZrO3 as evidenced by the very small enthalpy of mixing calculated based on the estimated ΔfHox. The values of standard entropy changes, ΔfSox, and Gibbs energy changes, ΔfGox, for the reactions of formation of BaZr1–xPrxO3 from BaO, ZrO2 and PrO2 were also estimated. Substituting Pr for Zr in BaZr1–xPrxO3 results in ΔfHox and ΔfGox becoming more positive, indicating the decrease of the relative stability with respect to the corresponding binary oxides. Expanded uncertainties of the estimated values of ΔfHox and ΔfGox are equal to 14 kJ∙mol-1, and those of S298 and ΔfSox – less than 2.8 J∙mol-1·K-1 and 3.5 J∙mol-1·K-1, respectively, for BaZr1–xPrxO3 (x = 0.0–1.0).

Double perovskites REBaCo2−xMxO6−δ (RE=La, Pr, Nd, Eu, Gd, Y; M=Fe, Mn) as energy-related materials: an overview

This work, based on the experimental and theoretical research carried out by the authors during the last decade, presents an overview of formation, stability and defect thermodynamics, crystal structure, oxygen nonstoichiometry, chemical strain and transport properties of the double perovskites REBaCo2−xMxO6−δ (RE = La, Pr, Nd, Eu, Gd, Y; M = Fe, Mn). These mixed-conducting oxides are widely regarded as promising materials for various energy conversion and storage devices. Attention is focused on (i) thermodynamics of formation and disordering, oxygen nonstoichiometry, crystal and defect structure of the double perovskites REBaCo2−xMxO6−δ, as well as their thermodynamic stability and the homogeneity ranges of solid solutions, (ii) their overall conductivity and Seebeck coefficient as functions of temperature and oxygen partial pressure and (iii) the anisotropic chemical strain of their crystal lattice. The relationships between the peculiarities of the defect structure and related properties of the double perovskites are analysed.