La0.8Sr0.2Ga0.8Mg0.2O2.8 powders were prepared by carbonate coprecipitation and the tuning of the cation composition by a solid state reaction. The relative compositions of La, Sr, Ga, and Mg were dependent upon the supersaturation ratio (R = [(NH4)(2)CO3]/([La3+] + [Sr2+] + [Ga3+] + [Mg2+])) during the coprecipitation. The coprecipitation of a Sr-deficient source solution and the subsequent replenishment of SrO and MgO by ball milling were effective for accomplishing a phase-pure La0.8Sr0.2Ga0.8Mg0.2O2.8 specimen by low-temperature sintering. (C) 2009 Elsevier B.V. All rights reserved.