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La_1−xSr_xGa_1−yMg_yO_3−δ (x=0.1–0.2, y=0.1–0.2) (LSGM) electrolytes, which have high ionic

conductivities, were synthesized by a solid-state reaction at 1500 °C. In our study,

La_0.9Sr_0.1Ga_0.9Mg_0.1O_3−δ and La_0.9Sr_0.1Ga_0.8Mg_0.2O_3−δ crystallized in an orthorhombic (Imma)

structure, and La_1−xSr_xGa_1−yMg_yO_3−δ (0.1<x≤0.2, 0.17≤y≤0.2) crystallized in a rhombohedral

(R3̄c) structure. Active Raman bands at approximately 532, 674, and 750 cm⁻¹ were

observed in these samples because of the decrease in local symmetry induced by the oxygen

vacancies. When x+y>0.35, the conductivity was approximately 0.164–0.173 S/cm at 800 °C.

The ionic conductivity mechanism changed at temperatures of approximately 500–650 °C.

La_0.9Sr_0.1Ga_0.9Mg_0.1O_3−δ and La_0.9Sr_0.1Ga_0.8Mg_0.2O_3−δ samples possessed higher resistances at

300–400 °C as a result of existing stacking faults and defects. The thermal expansion c

oefficients (TECs) were approximately 9.1×10⁻⁶/°C to 11×10⁻⁶/°C at 200–500 °C.
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