Effects of lanthanum on the electrical conductivity of CuO ceramics

Lanthanum was dissolved in CuO and the effects of La on the electrical conductivity of CuO were investigated in order to control the hole concentration and clarify the conduction mechanism of CuO that exhibits a p-type semiconductivity. The maximum amount of La dissolved in CuO was evaluated to be 0.5 mol% by powder X-ray diffraction. The conductivities for La-doped CuO were investigated by 4-probe and 3-probe methods. The temperature dependence of conductivity showed that CuO has two conduction mechanisms in the temperature range of 50 degrees C to 900 degrees C; conductivity at more than 600 degrees C was independent of atmosphere and the amount of La, whereas conductivity below 500 degrees C increased with an increase in partial oxygen pressure (P-O2) and amount of La. Surface conductivity at 200 degrees C was especially influenced by P-O2, and the sensitivity of surface conductivity to P-O2 increased with doping of La into CuO. The doping of La led to a change of chemisorbed oxygen species from O-2(-) to O-2(-) and resulted in an increase in sensitivity to P-O2.