Tailoring the structural, thermal and transport properties of Pr2NiO4+δ through Ca-doping strategy

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+delta (x = 0-0.6) oxides synthesized by a modified co-precipitation method and sintered at 1250 degrees C. The samples were characterized by in situ XRD using synchrotron radiation, TGA, oxygen heteroexchange with (CO2)-O-18 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 (similar to 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.