  LSCF is a promising candidate for the cathode in SOFCs. Understanding the
microstructural characteristics is crucial to its application because they
predominately determine the performance and durability of the porous cathodes
and hence of the SOFCs. To date little work has been reported on its mechanical
properties and their correlation with the 3D microstructures. The main purpose
of this research was to study the mechanical properties of both films and bulk
samples, and to evaluate the effect of microstructural parameters, by means of
both experimental and numerical methods. Room-temperature mechanical properties
were investigated by nanoindentation. The elastic modulus of the bulk samples
was found to increase from 33.8 to 174.3 GPa and hardness from 0.64 to 5.32 GPa
as the porosity decreased from 0.45 to 0.05 after sintering at 900 to 1200C. It
was shown that reliable measurements of the true properties of the films were
obtained provided that the effects from both surface roughness and substrate
were minimised to neglected levels within a certain range of indentation depth
to film thickness ratio. The fracture toughnesses of bulk LSCF were determined
to increase from 0.51 to 0.99 MPam0.5. The microstructures of films were
characterised using FIB-SEM slice and view technique and the actual 3D
microstructure models of the porous films were reconstructed based on the
tomographic data obtained. Finite element modelling of the elastic modulus
agreed well with the nanoindentation results. The 3D microstructures were
numerically modified at constant porosity using cellular automaton method, so
that the influence on elastic modulus of factors other than porosity could be
evaluated. It was found that the heterogeneity of the pore structure has a
significant influence on the elastic properties computed using mechanical
simulation.
