Abstract
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 Cmc2(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.