La_0.9Sr_0.1Ga_0.8M_0.2O_3-δ (M = Mn, Co, Ni, Cu or Zn): transition metal-substituted derivatives of lanthanum-strontium-galliummagnesium (LSGM) perovskite oxide ion conductor

Abstract

Perovskite oxides of the general formula, La_0.9Sr_0.1Ga_0.8M_0.2O_3-δ for M = Mn, Co, Ni, Cu and Zn, have been prepared and investigated. All the oxides exhibit high electrical conductivities (s R~ 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) (s ~ 8 × 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 (pO₂ ≥ 1 atm), arising from mixed-valency of the transition metals, the M = Zn(II) phase is a pure oxide ion conductor exhibiting a conductivity (σ ~ 1.5 × 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.