La0.8Sr0.2Ga0.8Mg0.2O3 (-) delta (LSGM) powders with various types of A-site deficiencies were synthesized and then their reactivities with Ce0.9Gd0.1O3 (-) delta (GDC) were compared. There were 4 types-12 sorts of prepared powders, i.e., normal LSGM La0.8Sr0.2Ga0.8Mg0.2O2.8; La deficient LSGM; La and Sr deficient LSGM, the La/Sr ratio fixed at 0.8/02; the La and Sr deficient LSGM, and the oxygen amount fixed at 2.8. Each of the LSGM powders with different types of A-site deficiencies was mixed with the GDC powder and thermally treated in air. The formation of the reacted phases during the thermal treatment was characterized by comparing their XRD spectra. The XRD patterns indicated that the effect of the suppression of the reactivity of LSGM was clearly confirmed; the effect is much more remarkable by keeping the oxygen amount the same as LSGM8282 (oxygen amount = 2.8). The most reaction-suppressed sample was La0.8Sr0.2Ga0.8Mg0.2O2.8 (A-site cation = 0.95, 0 = 2.8). The electric measurement revealed that the La0.8Sr0.2Ga0.8Mg0.2O2.8 exhibited a low chemical reactivity with GDC, while maintaining a modest level of electric conductivity. (c) 2014 Elsevier B.V. All rights reserved.