Lanthanum silicate thin films for SOFC electrolytes synthesized by magnetron sputtering and subsequent annealing

Thin films of La and Si with Si/(La + Si) atomic ratios ranging from 0.36 to 0.44 were produced by magnetron sputtering in pure Ar. For all compositions, the apatite-like La9.33Si6O26 phase was formed during annealing in air at 900 °C. A preferential orientation was developed during annealing of the films with higher silicon content while formation of oxide impurities was detected for the films with less silicon. Silicon segregation to the thin film/substrate interface was observed after annealing for thin films with higher Si/(La + Si) atomic ratios. The higher ionic conductivity values were obtained with the films with lower silicon content (2.81 × 10− 3 Scm− 1 at 800 °C for the film with Si/(La + Si) atomic ratio of 0.36). This film presented the lower activation energy Ea (0.94 eV).

► Crystalline La9.33Si6O26 is obtained after annealing the as-sputtered La–Si films at 900 °C for 1 h.
► A preferred orientation of the La9.33Si6O26 phase is observed in Si rich films.
► Higher ionic conductivity and lower activation energy are obtained in lower Si content films.