Chemical expansion of praseodymium-cerium oxide films at high temperatures by laser doppler vibrometry

The chemical expansion of Pr0.1Ce0.9O2−δ (PCO) films was determined as function of oxygen activity at 720 °C by laser Doppler vibrometry (LDV) in combination with previously reported chemical capacitance studies that provided relevant oxygen nonstoichiometry δ data. The LDV method enabled detection of nanometer displacements, provided that displacement frequencies were above 1 Hz. The PCO films were deposited on yttrium stabilized zirconia (YSZ) substrates operated in the electrochemical oxygen pump mode at 720 °C to periodically adjust the oxygen activity within the PCO film. The potential across the YSZ was varied between 0 and 0.3 V, corresponding to oxygen partial pressures of about 0.2 bar and 10−7 bar, respectively. The electrochemically induced expansion/contraction of the PCO film was observed to induce deflection in both film and substrate, as clearly demonstrated by scanning the sample surface by the LDV. A maximum displacement of about 18 nm at the center of the substrate plate was found during application of a periodic 1 Hz pumping voltage. A much lower displacement, on the order of 1 nm, was obtained when a pin-type sample support was applied, characteristic of chemical expansion of the film itself. These data were used to discuss correlations with similar recent data obtained by monitoring displacements of the PCO/YSZ sandwich structure with the aid of a specially modified nanoindenter.