Mechanical Properties of La _{1‐ <i>x</i>} Sr _<i>x</i> Co _0.2 Fe _0.8 O ₃ Mixed‐Conducting Perovskites Made by the Combustion Synthesis Technique

Abstract

This paper examined the room‐temperature mechanical properties of a mixed‐conducting perovskite La 1– x Sr x Co 0.2 Fe 0.8 O 3 ( x = 0.2–0.8). Powders were made by the combustion synthesis technique and sintered at 1250°C in air. Sintered density, crystal phase, and grain size were characterized. Young's and shear moduli, microhardness, indentation fracture toughness, and biaxial flexure strength were determined. The Young's and shear moduli slightly increased with increasing strontium content. Young's modulus of 151–188 GPa and shear modulus of 57–75 GPa were measured. Biaxial flexure strength of ∼160 MPa was measured for lower strontium content batches. Strength greatly decreased to ∼40 MPa at higher strontium concentrations ( x = 0.6–0.8) because of the formation of extensive cracking. Indentation toughness showed a higher value (∼1.5 MPa·m 1/2 ) for low strontium ( x = 0.2) content and a lower value (∼1.1 MPa·m 1/2 ) for the other batches ( x = 0.4–0.8). Materials with fine and coarse grain size were also tested at various indent loads and showed no dependence of toughness on crack size. In addition, fractography was used to characterize the critical flaw and fracture mode.