ELECTRICAL-PROPERTIES OF UNDOPED COO - A DEBYE-HUCKEL APPROACH

Thermopower and electrical conductivity data for both single crystal a nd polycrystalline undoped CoO are considered in terms of a defect dis order model based on doubly ionized cobalt vacancies as the predominan t defects. The analysis, based on the Debye-Huckel theory for liquid e lectrolytes, aims at an evaluation of the interactions between defects such as doubly ionized cation vacancies. It was shown that, in the te mperature range 1200-1700 K, the reciprocals of the partial pressure o f oxygen p(O-2) exponent of thermopower and electrical conductivity va ry between 3.6 < n(alpha) < 4.2 and 3.5 < n(sigma) < 3.8, respectively . About 1300 K, both n(alpha) and n(sigma) are higher for single cryst al than for the polycrystalline specimens. It was shown that closer ag reement between the defect model and experimental data can be obtained by introducing defect activities instead of concentrations.