Structure, stability, and thermomechanical properties of Ca-substituted Pr$_{2}$NiO$_{4+\delta}$

Ca-substituted layered nickelates with a general Pr$_{2}$NiO$_{4+\delta}$ composition ($x$ = 0–0.7, $\Delta x$ = 0.1) were prepared in the present work and their structural and physic-chemical properties were investigated in order to select the most optimal materials, which can be used as cathodes for solid oxide fuel cells. With an increase in Ca content in Pr$_{2}$NiO$_{4+\delta}$ the following tendencies were observed: (i) a decrease in the concentration of nonstoichiometric oxygen $(\delta)$, (ii) a decrease in the unit cell parameters and volume, (iii) stabilization of the tetragonal structure, (iv) a decrease of the thermal expansion coefficients, and (v) enchancement of thermodynamic stability and compatibility with selected oxygen- and proton-conducting electrolytes. The Pr$_{2}$NiO$_{4+\delta}$ material, having highest $\delta$ value, departs from the general “properties–composition” dependences ascertained. This indicates that oxygen non-stoichiometry has determining influence on the functional properties of layered nickelates.