Correlation between high ionic conductivity and twin structure of La0.95Sr0.05Ga0.9Mg0.1O3−δ

Abstract

The electric transport properties of La0.95Sr0.05Ga0.9Mg0.1O3−δ (LSGM) crystal with ⟨001⟩p direction grown by the Czochralski method were investigated mainly using ac measurements. The LSGM crystal comprises twin structures composed of different domain states. Only the highest-frequency semicircle was observed in impedance spectroscopy; however, two dielectric relaxation peaks exist in the loss tangent. These results indicate that the equivalent circuit of the twin structures is a parallel R-C circuit because they exhibit two parallel diffusion paths of O2− ions: one path is within the domains and the other is along the domain walls. Based on the migration energies of O2− in the domains and along the domain walls, which are estimated from dielectric relaxation processes, resistances of ionic conductions therein are assessed separately. These assessments explain that low resistance for oxygen ionic conduction along the domain walls considerably reduces the resultant resistance of the LSGM crystal and oxygen vacancies segregate preferentially in domain wall zones. A comparison between these results and those of a polycrystalline LSGM ceramic obtained experimentally suggests that the twin structures within the grains in ceramic lanthanum gallates are one of the main reasons for the high ionic conductivity.