Fe-doped apatite-type lanthanum silicate (La10Si6-xFexO27): synthesis, mixed conduction, and limiting-current oxygen sensor performance

La-excess-type lanthanum silicate doped with Fe (La 10 Si 6- x Fe x O 27 , x  = 0, 0.2, 0.4, 0.6) was synthesized through planetary ball milling. The resulting materials were systematically characterized for their crystal structure, infrared spectral features, microstructural properties, and electrical conduction behavior. It is revealed that La 10 Si 6- x Fe x O 27 remains apatite type, and Fe is doped into Si site. The surface particles of the La 10 Si 6- x Fe x O 27 ceramic sample are without holes, and the particles are arranged tightly and evenly. The element distribution of La 10 Si 6- x Fe x O 27 ceramic samples is uniform, and the element content conforms to the stoichiometric ratio. Both total and electronic conductivities exhibit a gradual enhancement with increasing iron content. A sensor was fabricated using dense diffusion barrier of La 10 Si 5.4 Fe 0.6 O 27 and solid electrolyte of La 10 Si 6 O 27 . Limiting current meets certain relationship with temperature and oxygen volume fraction, such as lg I L (mA) =  − 0.56 − 1.36 × 1000/ T (K −1 ) and I L (mA) = 3.10 + 0.69 ×  \(\varphi\) (O 2 ) (%). The sensor exhibits CO 2 /H 2 O-insensitive limiting current.