Mixed conducting perovskite-like ceramics on the base of lanthanum gallate

Ceramic perovskite solid solutions (La0.9Sr0.1)[(Ga1−xMx)0.8Mg0.2]O3−y, 0 ≤ x ≤ 0.5, M = Fe, Ni, Cr (systems I–III) and brownmillerite solid solutions (La0.2Sr1.8)[Ga(Fe1−xMgx)]O5−z, 0 ≤ x ≤ 0.5, (system IV) have been prepared. The samples have been studied by X-ray diffraction and electron microscopy methods, dielectric spectroscopy and permeability measurements. The correlation between the composition, unit cell parameter changes, electrical transport and oxygen permeation properties has been revealed. Introduction of transition metals (Fe, Ni, or Cr), substituting for gallium, ensures the enhancement of the electronic constituent of the conductivity in the perovskite systems I–III. Stabilization of the transition metal high valence states 4+ or 5+ has been suggested for compositions I and III. This leads to a unit cell volume contraction and provides a decrease in the concentration of oxygen vacancies. The oxygen permeability reaches its maximum values in compositions I–III with x ∼ 0.3. On the contrary, increasing concentration of the doping element with lower valence state (magnesium), substituting for iron, determines the expansion of the brownmillerite unit cell volume and provides an increase of the oxygen vacancy concentration, which in turn, favors the enhancement of oxygen permeability of composition IV.