High-Temperature Defect Structure and Electrical Properties of NiO

Abstract

The electrical conductivity and the Seebeck coefficient of single-crystal and polycrystalline NiO were measured as a function of temperature and of oxygen partial pressure over a large part of the phase field of stable NiO. In the temperature range 1000°–1600°C the electrical conductivity was found to be proportional to the fourth root of the oxygen partial pressure. This pressure dependence is that which one would expect for pure, nonstoichiometric NiO containing singly ionized metal vacancies as the predominant point defects. The activation energy for conduction, ΔHc, computed from σ = σ0exp (−ΔHc / kT), was found to be 0.92 ± 0.02 eV. The Seebeck coefficient of NiO was found to be p type over the entire range of temperatures and oxygen partial pressures measured. From the temperature dependence of the Seebeck coefficient, the enthalpy of formation of defects in NiO was calculated to be 0.66 ± 0.03 eV. From the measured temperature dependence of the electrical conductivity and the Seebeck coefficient it was found that the charge-carrier mobility increases with the temperature. Considering the drift mobility to be of the form μp∝T−1exp(−ΔHm / kT) a value of 0.37 eV could be attributed to the activation energy for motion of the charge carrier, ΔHm. The existence of such an activation energy supports the suggestion of a hopping process for the charge-carrier transport mechanism in NiO above about 1000°C.

Deposition of NiOx thin films with radio frequency magnetron sputtering and their characteristics as a source/drain electrode for the pentacene thin film transistor

“…19,[22][23][24] Many Ni 2+ vacancies exist in the nonstoichiometric NiO x film, and some Ni 2+ ions are oxidized to Ni 3+ ions to keep the charge near the Ni 2+ vacancies to be natural. 18 The excess oxygen ͑interstitial oxygen͒ in the NiO x film creates Ni 2+ vacancies and subsequently Ni 2+ vacancies are ionized with the formation of Ni 3+ ions and holes.…”

Oxidation of nickel during plasma spraying and some properties of nickel oxide

“…Chemical analysis [15] and photoelectron spectroscopy [16] of non-stoichiometric NiO have proved the presence of Ni 3+ ions. The measurements of conductivity as a function of oxygen partial pressure at constant temperature [17] have mostly given a dependence somewhat different from that typical of doubly charged vacancies in the above equation. To explain this, it has been suggested that vacancies (Ni) with a single elemental charge are also present.…”

High‐Temperature Oxidation

“…Similar approaches can be applied to nonstoichiometric compounds with cation vacancies (Cu 2-d O-type oxide), oxygen interstitials (UO 2 þ d -type oxide), and so on [80,[82][83][84][85][86].…”