Voltage‐Controlled Nonstoichiometry in Oxide Thin Films: Pr 0.1 Ce 0.9 O 2−δ Case Study

While the properties of functional oxide thin films often depend strongly on oxygen stoichiometry, there have been few means available for its control in a reliable and in situ fashion. This work describes the use of DC bias as a means of systematically controlling the stoichiometry of oxide thin films deposited onto yttria‐stabilized zirconia substrates. Impedance spectroscopy is performed on the electrochemical cell Pr 0.1 Ce 0.9 O 2−δ (PCO)/YSZ/Ag for conditions: T = 550 to 700 °C, pO 2 = 10 −4 to 1 atm, and ΔE = ‐100 to 100 mV. The DC bias ΔE is used to control the effective pO 2 or oxygen activity at the PCO/YSZ interface. The non‐stoichiometry ( δ ) of the PCO films is calculated from the measured chemical capacitance ( C chem ). These δ values, when plotted isothermally as a function of effective pO 2 , established, either by the surrounding gas composition alone, or in combination with applied bias, agree well with each other and to predictions based on a previously determined defect model. These results confirm the suitability of using bias to precisely control δ of thin films in an in situ fashion and simultaneously monitor these changes by measurement of C chem . Of further interest is the ability to reach effective pO 2 s as high as 280 atm.