LaFe_1–<i>x</i>Ni_<i>x</i>O_3−δ Preparation via Molten Salt Synthesis and Application in Limiting Current Oxygen Sensors

LaFe1–xNixO3−δ (x = 0–0.5) mixed conductor materials were synthesized using molten salt synthesis with NaCl–KCl composite molten salt. The crystal structure, microstructure, reaction mechanism, and electronic conductivity were systematically investigated. XRD analysis confirms the formation of an orthorhombic perovskite phase. SEM revealed that the grains exhibit a regular tetragonal morphology. Electronic conductivity analysis reveals that the electronic conductivities of all samples meet the linear relationship with 1000/T at 650–830 °C. The composition with a Ni element doping concentration of x = 0.3 exhibits higher electronic conductivity. The limiting current oxygen sensor was fabricated using LaFe0.7Ni0.3O3−δ as a dense diffusion barrier and 8 mol % yttria-stabilized zirconia (8YSZ) as the solid electrolyte assembled by the Pt sintered-paste method. The sensor exhibited stable operation at 760–850 °C and provided a 1–14 mol % oxygen measuring range. The oxygen sensor demonstrated excellent stability in limiting current and response time during 120 h of continuous operation at 850 °C.