Abstract: High temperature electrical conductivity of perovskite-type mixed with ionic-electronic conductor La_0.6Sr_0.4Co_0.2Fe_0.8O_3–δ  (LSCF) and La_0.6Sr_0.4Co_0.2Fe_0.8O_3–δ- Ce_0.9Gd_0.1O_1.95(LSCF-GDC) composite material were studied by the DC four-terminal technique. The activation energies of pure LSCF and LSCF-GDC composite for small polaron conduction were E_a1=9.72kJ/mol and E_a2=10.64kJ/mol, respectively. Through electrical conductivity relaxation method, i.e. a continuously resistance measurement during the sudden change oxygen under partial pressure and the surface exchange property of the two samples were also investigated. In the temperature range from 600℃ to 800℃ and the oxygen partial pressure range from 21kPa to 34kPa, the oxygen surface exchange coefficients (k_chem) were determined as 2.87×10^-6-6.91×10^-6cm/s. It is the catalysis effects of GDC on oxygen surface exchange process and the microstructure effect of introducing GDC that promoted the oxygen transport process of composite materials jointly. Based on the relationship of k_chem and temperature, the activation energies for surface exchange process was also estimated.

Key words: mixed conductor, electrical conductivity relaxation, activation energy, surface exchange coefficient