Mechanical properties of alkaline earth-doped lanthanum gallate

Lanthanum gallate doped with alkaline earths was prepared from combustion-s ynthesized powders. Mechanical properties of the doped gallates were evalua ted as a function of composition and temperature. The indentation fracture toughness of Sr-substituted gallates was significantly better than the Ca- and Ba-substituted materials, but the toughness of all the doped gallates w as significantly lower than yttria-stabilized zirconia, a typical electroly te material. Small improvements in room temperature toughness and strength were measured in (La0.9Sr0.1)(x)Ga0.8Mg0.O-2(3-delta), ("LSGM-1020") sample s with significant A-site cation non-stoichiometry (x = 0.9). The flexural strength of stoichiometric LSGM-1020 decreased from approximate to 150 MPa at room temperature, to approximate to 100 MPa at higher temperatures (600- 1000 degrees C). The notched-beam fracture toughness of LSGM-1020 decreased from approximate to 2.0-2.2 MPa root m at room temperature, to approximate to 1.0 MPa root m at 600 degrees C. The decrease in mechanical properties over this temperature range was correlated to changes in crystal structure that have been identified by neutron diffraction. These crystallographic ch anges were also accompanied by significant changes in the thermal expansion behavior and elastic modulus. For off-stoichiometric LSGM-1020 with A/B ca tion stoichiometry of 0.90, strength and toughness also decreased with temp erature, but the retained toughness (approximate to 1.5 MPa root m) at elev ated temperatures was higher than the toughness of the stoichiometric LSGM material. (C) 1999 Kluwer Academic Publishers.