The aim of this study was to develop La1-xBaxGa1-yMgyO3-delta (x = 0.03-0.1, y = 0.2-0.25) (LBGM) electrolytes for intermediate-temperature solid-oxide fuel cells (SOFCs); these electrolytes were synthesized via a solid-state reaction. In the study, the La1-xBaxGa1-yMgyO3-delta samples crystallized in an orthorhombic (Imma) structure, and a BaLaGa3O7 phase was detected for x >= 0.08 at a fixed y = 0.2. The solubility limit of the Ba ions increased with an increase in the Mg content in the matrix. Two active Raman bands at ca. 677 and 739 cm(-1) were observed, and they were attributed to the oxygen vacancies. The La0.95Ba0.05Ga0.75Mg0.25O3-delta sample had a higher conductivity ca. 0.1 S/cm at 800 degrees C, and an activation energy of ca. 0.83-1.27 eV at 500-800 degrees C. The thermal expansion coefficient (TEC) of the LBGM samples at 200-800 degrees C was in the range of 10 x 10(-6) to 14 x 10(-6)/degrees C. Copyright (C) 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.