Mechanical properties of calcium- and strontium-substituted lanthanum chromite

Mechanical properties of acceptor (calcium and strontium)-substituted lanth anum chromites are reported as a function of composition, temperature and e nvironment. The strength dependence on temperature for these perovskite con ductors was found to depend on the acceptor type, with the calcium-substitu ted chromites showing a significant reduction in strength with increasing t emperature, while the strength of strontium-substituted chromites was essen tially invariant with temperature. The decrease in strength observed upon a nnealing in highly reducing environments was correlated to changes in latti ce structure, stoichiometry and fracture morphology. A significant observat ion was the decrease in the cohesive strength of the grains relative to gra in boundaries, beyond a critical oxygen vacancy concentration in the chromi tes. The structural changes in the chromite lattice upon reduction also res ulted in decreased fracture toughness. (C) 1998 Chapman & Hall.