Chemical stability and cation stoichiometry determine the applicability of LaCr03 as a high-temperature oxide electrode. A model for the behavior of acceptor-doped LaCrO, as a function of oxygen activity is proposed. The model is in agreement with experimental data on Mg-doped LaCrO,. Stability regimes and compensation mechanisms at various oxygen activities and temperature are presented.

Measurements of the transport critical-current density (Jc), magnetization Jc, and magnetoresistance in a number of bulk sintered samples of Y1Ba2Cu3Ox from several different laboratories indicate that the transport Jc is limited by weak-link regions between high Jc regions. The weak-link Jc has a Josephson character, decreasing by two orders of magnitude as the magnetic field is increased from 0.1 to 10 mT at 77 K. An examination of the grain-boundary region in Y1Ba2Cu3Ox shows no observable impurities or second phases to the scale of the [001] lattice planes (∼12 Å). The effect of intrinsic conduction anisotropy is discussed. A current-transfer model is proposed in which weak conduction along the c axis plays a role in limiting Jc at grain boundaries. Orienting the grains in the powder state during processing may result in enhanced transport Jc in bulk conductors.

This paper summarizes the stress and fracture analyses of a three-layer ceramic composite which is a fundamental building block for the monolithic solid oxide fuel cell currently being developed at Argonne National Laboratory. A small difference in the coefficients of thermal expansion of different layers can result in large stresses and cause cracking parallel to the plane of the layers. A simple fracture model for a three-layer composite has been developed. The cracking behavior predicted by the model is in reasonably good agreement with the fabrication experience to date.