Proton conducting BaZr0.8Y0.2O3−x thin films by pulsed laser deposition technique

Here we report the synthesis of high-quality single-phase thin films of BaZr0.8Y0.2O3−x (BZY20) by pulsed laser deposition (PLD) technique. BZY20 films were deposited on various substrates including single-crystal sapphire (0 0 0 1), LaAlO3 (0 0 1), LaAlO3/LaNiO3 (0 0 1), and polycrystalline Cu and Fe foils. Depositions were performed using a high-power pulsed KrF excimer laser (wavelength 248 nm, 25 ns pulse duration) under controlled oxygen ambience. Substrate temperature and laser energy density during the depositions were maintained in the range 500–600 °C and 2–3 J/cm2, respectively. The microstructural, electrical, and gas-sensing properties of BZY20 films were studied, with the goal of understanding growth characteristics and optimizing their sensory response. X-ray diffraction (XRD) and orientation imaging microscopy (OIM) results showed that for BZY20 films grown on a sapphire (0 0 0 1) substrate, films tend to orient in the 〈1 1 1〉 and 〈2 1 1〉 directions, while for those grown on LaAlO3 (0 0 1) and LaAlO3/LaNiO3(0 0 1) substrates, films tend to orient preferably in the 〈2 1 1〉 direction. Possible atomic positions of the constituent atoms at the film/substrate interface were determined to understand the growth characteristics and to estimate the epitaxial strains at the film–substrate interface. Typical conductivity of BZY20 thin films grown on single-crystal substrates was ∼1×10−3 and ∼10×10−3 S/cm at 500 and 800 °C, respectively. BZY20 films grown on single-crystal substrates were found to be very sensitive to H2O vapor pressures with film resistance changing by >18% at temperatures of 400 °C when water vapor partial pressure changed from 2 to 50 kPa.