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.

Phase Transitions and Transport Properties of the Bismuth Vanadate-Based (Bi,La)4(V,Zr)2O11-zCeramics

“…This behavior may be indicative of the additional contribution of the ionic transport provided by the oxygen vacancies "pinned" at ferroelectric domain walls (or twin walls [20,21]) to the common mechanism of fast ionic migration through vacant positions in the oxygen sublattice [22,23] in the temperature domain of ferroelectric α-phase stability.…”

Identification of the Domain Walls Configuration in the Ferroelastic Nanosize Material La0.95Sr0.05Ga0.9Mg0.1O3-x

“…Hence, such pressure will cause texturing of twin "chevrons" in electrolyte layers along the direction of oxygen diffusion in the SOFC structure. Keeping in mind the influence of twin walls on the conductivity and the high density of twin walls in LSGM05 [7,8], we suppose that texturing of the twin structure, e.g. reorientation of "chevron cells" increases the conductivity of the perovskite-type electrolyte LSGM in the cathode-anode direction.…”

“…This distribution remains stable because the migration of vacancies and ions in the crystal structure at temperatures about 750 K is small. Taking into account the segregation of oxygen vacancies at domain walls, it has been assumed that the high ionic conductivity of LSGM compounds is caused by two simultaneous processes of oxygen diffusion: through the volume of the domains and fast along the domain boundaries [7,8].…”

“…Literature search shows that all oxide electrolytes with high ionic conductivity show typical martensitic phase transitions which produce nanosize ferroelastic domain structures [2][3][4][5][6]. The high ionic conductivity of heavy-twinned electrolyte materials can be explained by different transport properties of domain walls and bulk areas of such compounds [7,8].…”

Theoretical Study of the Ferroelastic Domain Structure in La0.95Sr0.05Ga0.9Mg0.1O3-x

“…Impurities can also be localized in a domain wall or close to it [13][14][15]. Different transport properties of domain walls and bulk materials can provide the explanation for high ionic conductivity of heavy-twinned perovskites and lanthanum galate doped with strontium and magnesium in particular [16,17].…”