Papers by Keyword: Oxide Ion Conductor

Abstract: Apatite materials are interesting alternative solid oxide fuel cell (SOFC) electrolytes because of their open structure including tunnels for the diffusion of oxide ions and their good chemical stability. However, the conductivity was still relative low when it was used as SOFC in the intermediate operating temperature range. So the apatite-type lanthanum silicates/germanates and doping were widely researched for enhancing conductivity recently. This study reports the influence of Ga doping on conductivity of the apatite phase La9.33(SiO4)6O2 according to the formula La9.33+x/3(SiO4)6-x(GaO4)xO2 where 0  x  2. Samples were prepared by a sol-gel process. The conductivities of all compositions have been obtained by impedance spectroscopy analysis. The conductivity enhancement observed for moderate x values and illustrates further influenced by the tetrahedral cation sublattice and the La vacancies in optimizing the conductivity.

Abstract: We investigate the effect of cation size in the dc activation energy needed for oxygen ion conductivity, Edc, in highly disordered pyrochlore-type ionic conductors A2B2O7. Twenty compositions of general formula Ln2Zr2-yTiyO7 (Ln = Y, Dy and Gd) and Gd2-yLayZr2O7, were prepared by mechanical milling and their electrical properties measured by using impedance spectroscopy at different temperatures. We also evaluate, by using Ngai’s Coupling Model, the effect of cation radii RA and RB, on the microscopic potential-energy barrier, Ea, that oxygen ions encounter when jumping into neighboring vacant sites. We find that for a fixed B-site cation radius RB, both activation energies decrease with increasing A-site cation size, RA, as a consequence of the increment in the unit cell volume. In contrast, and for a given RA size, the dc activation energy Edc of the Ln2Zr2-yTiyO7 series increases when the average RB size increases. The latter behavior is explained in terms of the enhanced interactions among mobile oxygen ions as the structural disorder increases when RB approaches RA.

Abstract: The crystal structure and oxide ion conduction properties of La0.9Sr0.1Ga0.9Mg0.1O2.9 were compared with those of LaGa0.8Mg0.2O2.9 with the same oxygen vacancy concentration. Although La0.9Sr0.1Ga0.9Mg0.1O2.9 had a smaller free space through which oxide ions pass compared to LaGa0.8Mg0.2O2.9, the activation energy of oxide ion conduction in the former was lower. This was attributed to the large displacement of La and Ga in La0.9Sr0.1Ga0.9Mg0.1O2.9. The GaO6 octahedral tilts in the LaGaO3 perovskite structure were reduced by double doping with Sr and Mg. Reduction of the GaO6 octahedral tilt proved effective for oxide ion conduction.