Abstract
Scandium (Sc) and yttrium (Y) co-doped ZrO2 (ScYSZ) thin films were prepared on a SiO2-Si substrate via pulsed laser deposition (PLD) method. In order to obtain good quality thin films with the desired microstructure, various oxygen partial pressures ( from 0.01 Pa to 10 Pa and substrate temperatures (Ts) from 25 °C to 800 °C were investigated. X-ray diffraction (XRD) patterns results showed that amorphous ScYSZ thin films were formed at room substrate temperature while cubic polycrystalline thin films were obtained at higher substrate temperatures (Ts = 200 °C, 400 °C, 600 °C, 800 °C). Raman spectra revealed a distinct Raman shift at around 600 cm−1 supporting a cubic phase. However, a transition from cubic to tetragonal phase can be observed with increasing oxygen partial pressure. Photoemission spectroscopy (PES) spectra suggested supporting analysis that more oxygen vacancies in the lattice can be observed for samples deposited at lower oxygen partial pressures resulting in a cubic structure with higher dopant cation binding energies as compared to the tetragonal structure observed at higher oxygen partial pressure. On the other hand, dense morphologies can be obtained at lower (0.01 Pa and 0.1 Pa) while more porous morphologies can be obtained at higher (1.0 Pa and 10 Pa).
Highlights
Zirconia-based solid oxide electrolyte is one of the most widely used solid electrolytes for solid oxide electrochemical cells (SOEC)
The as-deposited ScYSZ thin films at about 25 ◦C or room temperature (RT) is amorphous and crystallization started at 200 ◦C, well-crystallized peaks can be observed from 600 ◦C to 800 ◦C
As shown in the X-ray diffraction (XRD) stacked patterns, similar peaks can be observed for the different oxygen partial pressures; more crystalline or high-intensity peaks are observable for the oxygen-deficient environment or lower oxygen partial pressure, PO2 = 0.01 Pa and 0.1 Pa, as compared to higher oxygen partial pressures peak intensities
Summary
Zirconia-based solid oxide electrolyte is one of the most widely used solid electrolytes for solid oxide electrochemical cells (SOEC). It is typically doped with a trivalent cation such as yttrium to create oxygen vacancies and to stabilize the cubic structure. Scandia-stabilized zirconia (ScSZ), on the other hand, is used as a solid electrolyte due to its remarkable higher ionic conductivity, almost 3x, as compared to YSZ; the high conductivity of the cubic phase ScSZ is limited to a narrow temperature range and with the cubic phase structural stability dependent on doping concentration and temperature [5,6,7,8]. ScYSZ thin film showed higher ionic conductivity (1.2 × 10−1) at 700 ◦C (0.7 eV activation energy) as compared to bulk solid electrolytes [8,13,15]
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