Some physico-chemical properties of pure and doped nickel oxide. Electrical conductivity and thermoelectric power measurements

Abstract

Relative values of a.c. conductivity for all the samples prepared, whether undoped or doped, are measured at temperatures in the range from room temperature to about 400°C. The activation energy obtained from the curve of log σ vs. 1/ T indicates that nickel oxide prepared at 1000°C is the most stoichiometric form. The high temperature range in these measurements does not reach the intrinsic region. The change in activation energy as a function of dopant concentration is very slow in the case of gallium, but is marked in the case of alluminium. For undoped samples, it is found that the starting values of thermoelectric power increase with increase in the preparation temperature, which is attributed to the different concentration of defects present. The measurements on the different doped samples reveal that doped nickel oxide is still p-type, except in the case of In-doped samples in which the sign of conduction changes to n-type.