Signature of Oxide-Ion Conduction in Alkaline-Earth-Metal-Doped Y3GaO6

We have studied alkaline-earth-metal-doped Y 3 GaO 6 as a new family of oxide-ion conductor. Solid solutions of Y 3 GaO 6 and 2% -Ca 2+ -, -Sr 2+ -, and -Ba 2+ -doped Y 3 GaO 6 , i.e., Y (3-0.06) M 0.06 GaO 6-δ (M = Ca 2+ , Sr 2+ , and Ba 2+ ), were prepared via a conventional solid-state reaction route. X-ray Rietveld refined diffractograms of all the compositions showed the formation of an orthorhombic structure having the Cmc 2 1 space group. Scanning electron microscopy (SEM) images revealed that the substitution of alkaline-earth metal ions promotes grain growth. Aliovalent doping of Ca 2+ , Sr 2+ , and Ba 2+ enhanced the conductivity by increasing the oxygen vacancy concentration. However, among all of the studied dopants, 2% Ca 2+ -doped Y 3 GaO 6 was found to be more effective in increasing the ionic conductivity as ionic radii mismatch is minimum for Y 3+ /Ca 2+ . The total conductivity of 2% Ca-doped Y 3 GaO 6 composition calculated using the complex impedance plot was found to be ∼0.14 × 10 -3 S cm -1 at 700 °C, which is comparable to many other reported solid electrolytes at the same temperature, making it a potential candidate for future electrolyte material for solid oxide fuel cells (SOFCs). Total electrical conductivity measurement as a function of oxygen partial pressure suggests dominating oxide-ion conduction in a wide range of oxygen partial pressure (ca. 10 -20 -10 -4 atm). The oxygen-ion transport is attributed to the presence of oxygen vacancies that arise from doping and conducting oxide-ion layers of one, two-, or three-dimensional channels within the crystal structure. The oxide-ion migration pathways were analyzed by the bond valence site energy (BVSE)-based approach. Photoluminescence analysis, dilatometry, Fourier transform infrared (FTIR) spectroscopy, and scanning electron microscopy studies were also performed to verify the experimental findings.