Effect of A-site cation nonstoichiometry on the properties of doped lanthanum gallate

Lanthanum gallate doped with Sr and Mg (LSGM) was synthesized using a combustion synthesis technique. The synthesized powders were sintered to high density in air, although excessively high sintering temperatures led to bloating of samples, possibly due to the volatilization of Ga2O from the perovskite structure. The electrical conductivity of sintered LSGM tended to decrease with increasing A/B cation nonstoichiometry. Under oxidizing conditions, the conductivity was almost completely ionic, but in reducing atmospheres a substantial electronic component was observed. It is likely that this electronic conduction resulted from the introduction of electronic charge carriers via the partial reduction of Ga from the trivalent to the divalent state. The flexural strength of LSGM with an A/B cation ratio of 1.00 was measured to be similar to 150 MPa at room temperature; the strength decreased to similar to 100 MPa at higher temperatures (600-1000 degrees C). The fracture toughness, as measured by notched beam analysis, was similar to 2.0-2.2 MPa root m at room temperature, decreasing to similar to 1.0 MPa root m at 1000 degrees C. (C) 1998 Published by Elsevier Science B.V. All rights reserved.