Solid oxide fuel cells: materials and technology

The dimensional stability of acceptor-substituted lanthanum and yttrium chromite and lanthanum manganite were evaluated over a wide range of temperatures, oxygen partial pressures, and compositions. The instability of yttrium chromite in reducing environments was directly related to the loss of lattice oxygen and the simultaneous reduction of Cr⁴⁺ to Cr³⁺ to maintain electroneutrality. The evolution of oxygen and the reduction of chromium resulted in a lattice expansion, caused by the size change associated with the Cr⁴⁺ to Cr³⁺ transition and electrostatic repulsion between adjacent oxygen octahedra. The loss of lattice oxygen also results in dramatic decreases in the strength of lanthanum chromite in reducing environments. Lanthanum manganite was found to continue to sinter at temperatures as low as 1000°C. The effect of sintering on the sample was manifested in a shrinkage or expansion depending on the type and concentration of impurities in the sample, its composition, and stoichiometry