Effect of annealing on the fracture behavior of La0.58Sr0.4Co0.8Fe0.2O3‐δ, a potential energy material for oxygen separation

The perovskite material La_0.58Sr_0.4Co_0.8Fe_0.2O_3‐δ, offers high oxygen permeability at elevated temperature and is considered as a potential material for oxygen separation membranes. It can enhance the efficiency of oxy‐fuel combustion at high temperatures (> 800 °C) and hence due to the high reliability demands, required by the long term operation at elevated temperatures, it requires a thorough investigation from the view point of structural stability. Aiming towards long term stability, the present work is a detailed and systematic study on the effect of annealing on the mechanical behavior of dense La_0.58Sr_0.4Co_0.8Fe_0.2O_3‐δ. The study reveals that the indentation fracture toughness of the material increases with increase in annealing temperature. In most of the indentation loads, the subsurface crack profile was Palmqvist in nature with low value of the ratio of crack length versus indentation size (c/a). A consistent pattern of variation of c/a and indentation fracture toughness (K_IC) at all indentation loads was observed. Systematic drop in c/a and subsequent increase in fracture toughness in the as prepared test pieces has been attributed to residual stress accumulation during preparation.