Crystallization and microstructure of yttria-stabilized-zirconia thin films deposited by spray pyrolysis

The crystallization and microstuctural evolution upon thermal treatment of yttria-stabilized zirconia (YSZ, Zr_0.85Y_0.15O _1-δ) thin films deposited by spray pyrolysis at 370 °C are investigated. The as-deposited YSZ films are mainly amorphous with a few crystallites of 3 nm in diameter and crystallize in the temperature range from 400 °C to 900 °C. Fully crystalline YSZ thin films are obtained after heating to 900 °C or by isothermal dwells for at least 17 h at a temperature as low as 600 °C. Three exothermic heat releasing processes with activation energies are assigned to the crystallization and the oxidation of residuals from the precursor. Microporosity develops during crystallization and mass loss. During crystallization the microstrain decreases from 4% to less than 1%. Simultaneously, the average grain size increases from 3 nm to 10 nm. The tetragonal phase content of the YSZ thin film increases with increasing temperature and isothermal dwell time. Based on these data, gentle processing conditions can be designed for zirconia based thin films, which meet the requirements for Si-based microfabrication of miniaturized electrochemical devices such as micro-solid oxide fuel cells or sensors. This paper presents the microstructural characteristics of YSZ thin films deposited by spray pyrolysis. After deposition, YSZ thin films are amorphous with some 3 nm sized crystallites having a microstrain of 4%. During heating, the YSZ starts to crystallize; at 600 °C about 40% of the crystallization enthalpy is released and the crystallites have grown to a size of 5 nm with 1% microstrain. The material is fully crystalline at 900 °C or, after 17 h, at 600 °C.