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Materials with a layered Ruddlesden–Popper structure having high oxygen mobility are promising for SOFC cathodes and oxygen separation membranes. This work aims at studying structural and transport features of Pr2-xCaxNiO4+δ (x = 0–0.6) oxides synthesized by a modified co-precipitation method and sintered at 1250 °C. The samples were characterized by in situ XRD using synchrotron radiation, TGA, oxygen heteroexchange with C18O2 and dc four-probe method. The phase transitions Fmmm ↔ I4/mmm were observed for all samples caused both by the temperature increase and oxygen loss. The electronic conductivity increases with Ca doping, while ionic conductivity varies in a complex manner remaining rather high (~10−3–10−1 S/cm), thus ensuring high values of ambipolar conductivity attractive for the practical application. The best ambipolar conductivity values at high temperatures were demonstrated for the undoped sample as well as for those with a low (x = 0.1) or high (x = 0.3; 0.5) dopant content. The relationships between structural, thermomechanical and transport properties are discussed.

Fine powders of Pr2 − xNiO4 + δ (PNO) oxides (x = 0 ÷ 0.3) synthesized by Pechini route were uniaxially pressed into pellets and sintered at 1300 °C under air. Chemical diffusion coefficients (Dchem.) and surface exchange constants (kchem.) were estimated by analysis of the weight and conductivity relaxations after step-wise change of pO2. In situ XRD studies were carried out in VEPP-3 facilities of the Siberian Center of Synchrotron Radiation using unique high-temperature camera and procedures. Analysis of dynamics of the cell volume expansion caused by oxygen loss with due regard for penetration depth of X-rays into the pellet allowed to estimate Dchem and kchem found to be close to those obtained by traditional methods. Isolated Pr vacancies appear to be the most important for fast oxygen diffusion and high surface reactivity providing the highest values of kchem and Dchem for Pr1.9NiO4 + δ composition.