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

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.

Influence of Mg‐substitution on structural and electrical properties of ion‐conducting Ca‐doped tri‐yttrium gallate

“…However, the slight increase in the bandgap after x = .02 can be attributed to the presence of the impurity's concentration. The obtained values of bandgap are in good agreement with the literature 17 …”

“…This change in the intensity could be due to the presence of the Mg 2+ content, which introduces defects or disorders in the material. Our previous reports on Y 3 GaO 6 material say that aliovalent doping results in defect levels 17 . As Mg 2+ content increases, new oxygen vacancies are introduced, which affect the properties of the materials, and this phenomenon is also observed in UV–Vis absorption spectra.…”

“…The Y 3+ cations get localized in two different asymmetric sites with sevenfold coordination, and the Ga 3+ cation forms distorted oxygen tetrahedral. Y 3 GaO 6 with 2% of alkaline‐earth metal (Ca) doping shows a total conductivity of ∼.14 × 10 −3 S cm −1 at 700°C, which is equivalent to many other solid electrolytes 17 . The conductivity is primarily ionic in the wide range of p O 2 from 10 −4 to 10 −20 atm.…”

“…Therefore, in search of new solid electrolytes, recently, we explored this new family of oxide ion conductors. In this family, alkaline‐earth metal‐substituted Y 3 GaO 6 was found to exhibit good ionic conductivity 17 . Y 3 GaO 6 is yttrium oxy‐monogallate for which whole chemical formulae can also be written as Y 3 O 2 GaO 4 .…”

Insight into Structural and Electrical Properties of Potassium and Lithium Substituted Non-stoichiometric Sodium Bismuth Titanate (Na0.54Bi0.46TiO3-δ)

“…So the conduction in all the compositions was found to three dimensional. The migration energy barrier for any system is defined as the energy difference between the energy maxima and local minima [15,16]. The migration barrier for oxide ion migration is 1.4 eV for N00 and is found to increase significantly with the K + and Li + doping.…”