Transport Properties of Mixed Ionic Electronic Conductors under Thermodynamically Equilibrated Conditions: Measurements on Porous Bodies

Electrical conductivity, thermoelectric power, and surface exchange coefficient were measured on porous oxide samples. The rationale for using porous instead of dense samples was that porous samples equilibrate with the imposed atmosphere much faster compared to dense samples due to rapid gas phase transport through pores and rapid solid state transport into micron sized particles of porous samples. Experiments were conducted on Gd2O3-doped CeO2 (GDC), Sm2O3-doped CeO2 (SDC), K and Y doped BaZrO3, and Sr-doped LaCoO3 (LSC). Thermoelectric power was also measured on silver for comparison. Chemical diffusion coefficient of oxygen was measured by conductivity relaxation on a dense sample with porous surface layers. The results showed that in all cases, the use of porous samples, or dense samples with porous surface layers, facilitated rapid equilibration and allowed the measurement of properties under thermodynamically equilibrated conditions.