Ytterbium-doped Barium Zirconate Thin Films by Pulsed Laser Deposition for Intermediate Temperature Solid Oxide Fuel Cell Applications

Ytterbium-doped barium zirconate (BZYb) is predicted to have high protonic conductivity and good potential as a thin-film electrolyte material for intermediate temperature (500-750$^{\circ}$ C) solid oxide fuel cells. We have synthesized BZYb thin films by pulsed laser deposition using ablation targets prepared by mixing barium zirconate (BaZrO$_{3})$ and ytterbium oxide (Yb$_{2}$O$_{3})$ powders. Powders had their masses varied to produce targets with 5, 10, and 15 mol.{\%} of Yb in BaZrO$_{3}$. Targets where pressed at 2800 psi and annealed at 1200$^{\circ}$ C for 12 hours in air. Thin films 1-2 $\mu $m thick were deposited on Si and MgO substrates at 600$^{\circ}$ C using a KrF excimer laser with energy density of 1-2 J/cm$^{2}$ and repetition rate of 30 Hz. Deposition took place at a pressure of 50 mTorr of O$_{2}$ in a vacuum system with base pressure below 5.0x10$^{-7}$ Torr. X-ray diffraction from as-deposited films show patterns of polycrystalline cubic BaZrO$_{3}$ on both, Si and MgO substrates. A substantial amount of amorphous material is present in as-deposited samples. Post-deposition annealing in air at 800\textordmasculine C greatly improves film crystallinity with virtual elimination of the amorphous phase. Energy dispersive X-ray measurements indicate the successful incorporation of Yb in the films in concentrations of 3.1, 5.5, and 8.8 mol.{\%} for targets prepared with 5, 10, and 15 mol.{\%} of Yb, respectively.