Functional properties and structure-size factor in La1.4A0.6Ni0.6Fe0.4O4+δ (A=Ca, Sr, Ba)

La1.4Ca0.6Ni0.6Fe0.4O4+δ (LCNF), La1.4Sr0.6Ni0.6Fe0.4O4+δ (LSNF), La1.4Ba0.6Ni0.6Fe0.4O4+δ (LBNF) have been synthesized by the citrate-nitrate technique. The X-Ray powder diffraction (XRPD) results show an increase in the unit cell parameters and the unit cell volume with the increase in radius of the alkaline earth metal. The oxides possess oxygen excess equal to 0.06 at room temperature and demonstrate semiconductor-type behavior in the 25–950 °C range. The thermal expansion coefficient (TEC) determined in the 200–1000 °C interval decreases from 13.9×10−6 (A=Ca) to 13.2×10−6 К−1 (A=Ba) with increasing the dopant size. The electrochemical studies have revealed that the overall polarization resistance of La1.4A0.6Ni0.6Fe0.4O4+δ is equal to 1.85, 2.61 and 0.4 Ω cm2 at 800 °C for A=Ca, Sr and Ba, respectively. The predominant contribution to the polarization resistance is assigned to the charge transfer – ionic diffusion in the electrodes. It decreases in the row LSNF-LCNF-LBNF, which correlates with the increase in ionic conductivity in the oxides. •La1.4(Ca/Sr/Ba)0.6Ni0.6Fe0.4O4+δ show oxygen excess and similar total conductivity.•La1.4A0.6Ni0.6Fe0.4O4+δ have moderate TEC values ranging from 13.2 to 14.1 × 10–6K–1.•Oxygen diffusion coefficient in La1.4A0.6Ni0.6Fe0.4O4+δ increased in the row Sr-Ca-Ba.•Polarization resistance of the oxides correlated with the oxygen diffusion rate.•La1.4Ba0.6Ni0.6Fe0.4O4+δ shows polarization resistance of 0.4 Ω cm2 at 800 °C.