Effect of Rate on Pulsed Laser Deposition of Yttria-Stabilized Zirconia Electrolyte Thin Films for SOFCs

Yttria-stabilized zirconia (YSZ) thin films were deposited by pulsed laser deposition (PLD) at laser repetition frequencies of 10–50 Hz. Controlling the laser repetition frequency can achieve high deposition rate of YSZ, but high deposition rate at high laser repetition frequency can adversely affect the crystallinity of the resulting film. In the present work, X-ray diffraction (XRD) of YSZ thin films deposited at 10–50 Hz unexpectedly indicated no significant differences. Well-crystallized YSZ thin films were obtained for all laser repetition frequencies. This result may be due to a sufficient substrate temperature of 1000 K during processing. The oxide-ion conductivity of each thin film was comparable to that of bulk YSZ. Only minor differences in Y2O3 content, residual stress, grain size, and grain-boundary width were observed among the films. We concluded that similar quality YSZ thin films were obtained at all deposition frequencies. Oxide-ion conductivity was affected by the temperature at which the substrate was deposited. The YSZ thin films deposited at 900 K and 1000 K showed similar oxide-ion conductivity and films deposited at 800 K showed lower oxide-ion conductivity. This difference could perhaps be due to narrow grain-boundary width. The YSZ thin film with highest oxide-ion conductivity was fabricated at an intermediate substrate temperature of 900 K with a deposition rate of 86 nm·min−1 at 50 Hz, without additional high-temperature annealing greater than 1273 K. The YSZ growth rates were faster than the rates for other gas-phase methods such as midfrequency and DC sputtering.