High ionic conductivity in CeO2 SOFC solid electrolytes; effect of Dy doping on their electrical properties.

Ionic conductors composed of lanthanide-doped ceria with general formula Dy y Ce 1-y O 2-δ (y = 0.05, 0.1 and 0.15) were synthesized by mechanochemistry (mechanical milling), and their electrical properties analyzed to be used as solid electrolytes in low-temperature SOFC. Starting oxide reagents were milled at different times in a planetary mill and the evolution of their structures and phases with milling time and temperature (up to 1500 °C) was followed by XRD. Just milled powders were also uniaxially pressed and sintered at different temperatures (1200, 1350 and 1500 °C), and analyzed by FE-SEM, to explore their morphologies as a function of temperature and Dy content. The electrical properties of these materials and undoped commercial CeO 2 were analyzed by impedance spectroscopy at different temperatures (200–650 °C) and frequencies (100 Hz - 1 MHz). Results showed that mechanochemistry is a suitable method to obtain the Dy y Ce 1-y O 2-δ systems after 20 h of milling, since XRD patterns of these milled powders reveal the formation of fluorite-type cubic solid solutions for all studied compositions. Increasing of temperature generates a higher crystallinity in these materials while the absence of phase transitions in them is corroborated at 1200 °C. Analysis of electrical properties of samples sintered a 1200 °C corroborates the viability of these systems to be used as solid electrolytes in the SOFC technology, being that high dc conductivities (σ dc) were obtained for all doped samples, especially for the composition Dy 0.1 Ce 0·9 O 2-δ , which showed a σ dc = 1 × 10−1.91 S cm−1 at 650 °C. This value represents an increase of almost three orders of magnitude for this composition with respect to the undoped CeO 2 sample (y = 0, σ dc = 1 × 10 −4.83 Scm−1). • CeO 2 doped with Dy was successfully synthesized by a mechanochemical reaction. • All compositions (5, 10 and 15% mol of Dy) show a cubic fluorite-type structure. • Electrical properties of the samples were measured as a function of temperature. • Conductivity (σ dc) reaches a maximum of 1 * 10−1.91 Scm−1 (650 °C) for 10% of Dy. • Increasing of σ dc is related to the creation of oxygen vacancies in the structure. [ABSTRACT FROM AUTHOR]