Electrical conductivity, Raman scattering (RS) spectra, and thermal expansion of the solid solution based on lanthanum gallate having the formula La0.88Sr0.12Ga0.82Mg0.18O2.85 (LSGM12-18) were studied as a function of temperature. X-ray diffraction analysis (XDA) of the samples at room temperature was performed. A dilatometric examination demonstrated that phase transitions of the second order took place at 775+/-10 and 880+/-20 K. The transition at 880 K was confirmed both by Raman scattering spectra and by a change in the activation energy of the electrical conductivity. This phase transition is probably due to a change of the oxygen sublattice symmetry. (C) 2003 Elsevier B.V. All rights reserved.