La0.9Sr0.1Ga0.8M0.2O3-δ (M = Mn, Co, Ni, Cu or Zn): Transition metal-substituted derivatives of lanthanum-strontium-galliummagnesium (LSGM) perovskite oxide ion conductor

Perovskite oxides of the general formula, $La_0.9Sr_0.1Ga_0.8M_0.2O_3–\delta$ for M = Mn, Co, Ni, Cu and Zn, have been prepared and investigated. All the oxides exhibit high electrical conductivities $(\sigma ~ 10^–2 S/cm at 800°C)$ comparable to that of the best perovskite oxide ion conductor, $La_0.9Sr_0.1Ga_0.8Mg_0.2O_2.85$ (LSGM)$(\sigma ~ 8\times 10^–2 S/cm at 800°C)$. While M = Mn, Co, Ni, Cu members appear to be mixed conductors with a variable electronic contribution to the conductivity, especially at high oxygen partial pressures $(pO_2 \geq 1 atm)$, arising from mixed-valency of the transition metals, the M = Zn(II) phase is a pure oxide ion conductor exhibiting a conductivity $(\sigma ~ 1.5 \geq 10^–2 S/cm at 800°C)$ that is slightly lower than that of LSGM. The lower conductivity of the M = Zn(II) derivative could be due to the preference of Zn(II) for a tetrahedral oxygen coordination.