High-temperature defect structure and electrical conduction in Ni 1− xMg xO

Abstract

The ionic transference number, the electrical conductivity, and Seebeck coefficient of Ni 1− x Mg x O (0.1 ≤ x ≤ 0.9) were measured as functions of temperature (900–1400°C) and oxygen partial pressure (10 2–10 5 Pa). The contribution of ionic conduction to the total conductivity of Ni 0.9Mg 0.1O was of the order of 10 −3−10 −2 at 900–1300°C, which led us to assume that the electronic conduction was predominating in Ni 1− x Mg x O ( x ≤ 0.9). The electrical conductivities of both undoped and Al-doped Ni 1− x Mg x O depended on the 1 4 power of P O 2 , which indicated a significant impurity effect on the defect equilibria and was interpreted as showing that doubly ionized cation vacancies were the dominant point defects at high temperatures. Analyses of the difference in the temperature dependences of conductivity and Seebeck coefficient showed that band-like conduction took place in the NiO-rich composition range ( x ≤ 0.1), while thermally activated hopping of small polarons occurred in Ni 1− x Mg x O with x ≥ 0.3. The calculated drift mobility abruptly decreased in the composition region where the conduction mechanism changed.