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In this study, the structural and electrochemical properties of commercial powders of the nominal compositions Ce0.8Gd0.2O1.9, Sc0.1Ce0.01Zr0.89O1.95, and Sc0.09Yb0.01Zr0.9O1.95 were investigated. The materials are prospective candidates to be used in electrochemical devices, i.e., gas sensors and fuel cells. Based on a comparison of the EIS spectra in different atmospheres (synthetic air, 3000 ppm NH3 in argon, 10% H2 in argon), the reactions on the three-phase boundaries were proposed, as well as the conduction mechanisms of the electrolytes were described. The Ce0.8Gd0.2O1.9 material is a mixed ionic–electronic conductor, which makes it suitable for anode material in fuel cells. Moreover, it exhibits an apparent and reversible response for ammonia, indicating the possibility of usage as an NH3 gas-sensing element. In zirconia-based materials, electrical conduction is realized by oxygen ion carriers. Among them, the most promising from an applicative point of view seems to be Sc0.09Yb0.01Zr0.9O1.95, showing a high, reversible reaction with hydrogen. [ABSTRACT FROM AUTHOR]

Gadolinium-doped ceria (GDC) nanopowders, prepared using the co-precipitation synthesis method, were applied as a starting material to form ceria-based thin films using the electron-beam technique. The scanning electron microscopy (SEM)analysis of the pressed ceramic pellets' cross-sectional views showed a dense structure with no visible defects, pores, or cracks. The AC impedance spectroscopy showed an increase in the total ionic conductivity of the ceramic pellets with an increase in the concentration of Gd2O3 in GDC. The highest total ionic conductivity was obtained for Gd0.1Ce0.9O2-δ (σtotal is 11 × 10−3 S∙cm−1 at 600 °C), with activation energies of 0.85 and 0.67 eV in both the low- and high-temperature ranges, respectively. The results of the X-ray photoelectron spectroscopy (XPS) and inductively coupled plasma optical emission spectrometer (ICP-OES) measurements revealed that the stoichiometry for the evaporated thin films differs, on average, by ~28% compared to the target material. The heat-treatment of the GDC thin films at 600 °C, 700 °C, 800 °C, and 900 °C for 1 h in the air had a minor effect on the surface roughness and the morphology. The results of Raman spectroscopy confirmed the improvement of the crystallinity for the corresponding thin films. The optimum heat-treating temperature for thin films does not exceed 800 °C. [ABSTRACT FROM AUTHOR]

Gadolinium-Doped Ceria (GDC) is a prospective material for application in electrochemical devices. Free sintering in air of GDC powder usually requires temperatures in the range of 1400 to 1600 °C and dwell time of several hours. Recently, it was demonstrated that sintering temperature can be significantly decreased, when sintering was performed in reducing atmosphere. Following re-oxidation at elevated temperatures was found to be a helpful measure to avoid sample failure. Sintering temperature and dwell time can be also decreased by use of Spark Plasma Sintering, also known as Field-Assisted Sintering Technique (FAST/SPS). In the present work, we combined for the first time the advantages of FAST/SPS technology and re-oxidation for sintering of GDC parts. However, GDC samples sintered by FAST/SPS were highly sensitive to fragmentation. Therefore, we investigated the factors responsible for this effect. Based on understanding of these factors, a special tool was designed enabling pressureless FAST/SPS sintering in controlled atmosphere. For proof of concept, a commercial GDC powder was sintered in this tool in reducing atmosphere (Ar-2.9%H2), followed by re-oxidation. The fragmentation of GDC samples was avoided and the number of micro-cracks was reduced to a minimum. Prospects of GDC sintering by FAST/SPS were discussed. [ABSTRACT FROM AUTHOR]