Mechanical behavior of La_0.8Sr_0.2Ga_0.8Mg_0.2O₃ perovskites

This paper examines the important mechanical properties of commercially purchased La_0.8Sr_0.2Ga_0.8Mg_0.2O₃ at room temperature and 800 °C. Sr and Mg-doped lanthanum gallates (LSGM) are strong candidates for use as solid electrolytes in lower temperature solid oxide fuel cells operating at or below 800 °C. The material was found to be phase pure with a Young's modulus value of ∼175 GPa. The four point bending strength of the LSGM samples remained almost constant from 121 ± 35 MPa at room temperature to 126 ± 20 MPa at 800 °C. The fracture toughness, as measured by the single edge V notch beam (SEVNB) method, was 1.22 ± 0.06 MPa√m at room temperature, 1.04 ± 0.09 MPa√m at 700 °C followed by a small increase 1.31 ± 0.16 MPa√m at 800 °C. We also report, for the first time, the static subcritical (or slow) crack-growth (SCG) behavior of natural cracks in LSGM performed in four point bending tests at room temperature. The exponent of a power-law representation in the SCG tests was found to be n = 15, a rather low value showing LSGM to be highly susceptible to room temperature SCG.