Electrical and electro-chemical characterisation of La_0.99Fe_1−x Ni _x O_3−δ perovskites

Abstract

${\text{La}}_{{{\text{0}}{\text{.99}}}} {\text{Fe}}_{{{\text{1 - x}}}} {\text{Ni}}_{{\text{x}}} {\text{O}}_{{{\text{3 - }}\delta }}$ (LFN, 0<x<0.6) perovskites were synthesised by a solid-state route and were characterised by powder XRD, dilatometry, four-point DC conductivity measurements and electro-chemical impedance spectroscopy (EIS) on cone-shaped electrodes using a Ce_1.9Gd_0.1O_1.95 (CGO10) electrolyte. All the compounds were of single phase, and they belong to either the cubic or the hexagonal crystal system. The thermal expansion coefficient (TEC) was in the range 10.7*10⁻⁶ K⁻¹ to 13.4*10⁻⁶ K⁻¹, which continued to increase with increasing nickel content. The highest electronic conductivity was measured for the composition ${\text{La}}_{{{\text{0}}{\text{.99}}}} {\text{Fe}}_{{{\text{0}}{\text{.4}}}} {\text{Ni}}_{{{\text{0}}{\text{.6}}}} {\text{O}}_{{{\text{3 - }}\delta }} {\text{,}}$ giving a value of 670 S/cm at 380 °C. The highest electro-chemical performance was measured for the composition ${\text{La}}_{{{\text{0}}{\text{.99}}}} {\text{Fe}}_{{{\text{0}}{\text{.4}}}} {\text{Ni}}_{{{\text{0}}{\text{.6}}}} {\text{O}}_{{{\text{3 - }}\delta }}$ giving an area specific resistance as low as 5.5 Ωcm² at 600 °C based on EIS measurements on a cone-shaped electrode. Composite cathodes made from ${\text{La}}_{{{\text{0}}{\text{.99}}}} {\text{Fe}}_{{{\text{0}}{\text{.4}}}} {\text{Ni}}_{{{\text{0}}{\text{.6}}}} {\text{O}}_{{{\text{3 - }}\delta }}$ and CGO10 revealed a rather low performance due to an un-optimised micro-structure.