The effects of the Ga incorporation on the crystal chemistry and high temperature properties of the n=3 Ruddlesden Popper system LaSr3Fe1.5-x/2Co1.5-x/2GaxO10-delta (0 <= x <= 0.8) have been investigated. As the Ga content increases the symmetry of the unit cell varies from tetragonal for the samples with x=0 and 0.3 to orthorhombic for the x=0.8 sample. Due to the fixed Ga+3 oxidation state, the substitution of Ga for Fe and Co increases the oxygen vacancy concentration in the samples at room temperature while it decreases the variation of the oxygen content with temperature. The total expansion coefficient of the LaSr3Fe1.5-x/2 Co1.5-x/2GaxO10-delta specimen in the temperature range 80 <= T <= 900 degrees C decreases with increasing Ga content due to the suppression of the chemical expansion at high temperature. Similarly, the electrical conductivity also decreases as the Ga content increases. The electrochemical performances of the LaSr3Fe1.5-x/2Co1.5-x/2 GaxO10-delta samples as cathode materials in SOFC have been tested with electrolyte-supported single cells using La0.8Sr0.2Ga0.8Mg0.2O2.8 (LSGM) as an electrolyte. Although the maximum power density of the cells decreases with increasing Ga content, the LaSr3Fe1.5-x/2Co1.5-x/2GaxO10-delta cathode provides an important advantage of decrease in total expansion with increasing Ga content. (C) 2010 Elsevier B.V. All rights reserved.