Electrical Conductivity of the Solid Solutions XNiO + (1 - X)Tm2O3 (0.01 X 0.05)

NiO‐doped Tm 2 O 3 systems (NDT) containing 1, 3, and 5 mol% NiO were found to be solid solutions by X‐ray diffraction (XRD) analysis. The lattice parameters ( a ) were obtained by the Nelson‐Riley method, and the values decreased with increasing dopant content. Thermal analysis showed that no phase transition occurred in the temperature range covered in this experiment. The electrical conductivities were measured in the range of temperatures from 400° to 1100°C and of oxygen partial pressures from 1 × 10 −5 to 2 × 10 −1 atm. The conductivity increases with temperature but there is a break in the conductivity curve, dividing it into two temperature regions. At the high temperatures of 700° to 1100°C, the activation energy ( E a ) and oxygen partial pressure dependence of conductivity are found experimentally to be 1.4 to 1.5 eV and 1/ n = 1/5.4, and the possible defects and charge carriers are suggested to be metal vacancies and electron holes, respectively. At the lower temperatures of 400° to 600°C, the E a and 1/ n values obtained are 0.8 to 0.9 eV and 1/ n = 1/7.2 to 1/8.8, respectively. At the lower temperature, the NDT system seems to display a mixed conduction involving ionic conductivity due to diffusion of oxygen.