Cation Self‐Diffusion and Semiconductivity in NiO
01 Aug 1970-Journal of Chemical Physics (American Institute of Physics)-Vol. 53, Iss: 3, pp 1117-1125
TL;DR: In this article, self-diffusion and semiconductivity in single-crystal NiO have been measured as functions of temperature and O2 pressure over ranges of 1182-1762°C and from one to 5'×'10−7 atm.
Abstract: Nickel self‐diffusion and semiconductivity in single‐crystal NiO have been measured as functions of temperature and O2 pressure over ranges of 1182–1762°C and from one to 5 × 10−7 atm. Atmospheres of pure O2, pure CO2, O2–Ar mixtures, and CO–CO2 mixtures have been used. In pure O2 and in pure CO2 the results can be expressed with a standard deviation of less than 4% by equations of the form D = D°exp(− ED / RT ) and σT = (σT)0exp(− Eσ / RT). In pure O2, D° = (4.8 ± 1.3) × 10−2cm2/sec, ED = 60.8 ± 0.6 kcal/mol, (σT)0 = (7.5 ± 0.8) × 106Ω−1·cm−1°K, Eσ = 24.7 ± 0.2 kcal/mol. In pure CO2, D° = (2.1 ± 0.4) × 10−2cm2/sec, ED = 62.7 ± 0.3 kcal/mol, (σT)0 = (65 ± 11) × 106Ω−1·cm−1/sz/K, Eσ = 36.4 ± 0.6 kcal/mol. Both semiconductivity and diffusion coefficients are proportional to Pβ. For diffusion, β increases with temperature, being 0.16 at 1245°C and 0.20 at 1380°C; for conductivity, β is between 14and16 and decreases with temperature. The results can be interpreted in terms of simple models invoking noninterac...
Citations
More filters
TL;DR: In this article, the authors report measurements of the oxide scale thickness and oxide grain size as a function of time during the oxidation of high-purity nickel in the temperature range 500-800°C.
Abstract: Below 1000°C the oxidation of nickel cannot be controlled by the diffusion of ions through the bulk crystal lattice of the pure oxide, because the measured oxidation rates are several orders of magnitude faster than would be predicted on this basis. Short-circuit diffusion through oxide grain boundaries or dislocations has usually been held responsible, but there has hitherto been no proper quantitative confirmation of this mechanism. We report measurements of the oxide scale thickness and oxide grain size as a function of time during the oxidation of high-purity nickel in the temperature range 500–800°C. All the oxidation experiments were carried out in pure oxygen at a pressure of one atmosphere. The measured parabolic oxidation rate constants have been compared with those calculated from grain boundary diffusion data obtained in our previous work, using a grain boundary diffusion model for the oxidation process. The quantitative agreement between measured and calculated oxidation rates shows c...
2,579 citations
TL;DR: In this paper, the suitability of both pure and Li-doped NiO as a thin-film resistive gas sensor for formaldehyde has been investigated, and the detection limit for the latter was found to be ≈40ppm.
Abstract: The suitability of both pure and Li-doped NiO as a thin-film resistive gas sensor for formaldehyde has been investigated. Pure NiO had a linear formaldehyde sensitivity of 0.825 mV ppm−1 while that for 0.5 at.% Li-doped NiO was 0.488 mV ppm−1 at 600°C. These gas-sensing materials also showed similar sensitivity for methanol and acetone as well as a reduced sensitivity for toluene and ethanol. Chloroform was a poison for these gas-sensing materials. Due to resistive noise, the detection limit for formaldehyde was found to be ≈40 ppm.
342 citations
TL;DR: In this article, the main part of this paper focuses on the more complex models suggested to account for experimental observations of the oxidation kinetics and the oxide morphology below 1000 °C.
194 citations
TL;DR: In this paper, the authors give an overview of different types of defects and defect structures in metal oxides and transport properties such as diffusion and electrical conductivity, and describe defect equations and equilibria.
Abstract: The paper gives an overview of different types of defects and defect structures in metal oxides and transport properties such as diffusion and electrical conductivity. Point defects (vacancies, interstitials, impurity and dopant ions, hydrogen ions, a.o.) and corresponding defect structures are described by defect equations and equilibria. Oxides of common use metals and which are of particular interest in many aspects of high-temperature oxidation of metals, e.g., cobalt and nickel oxides, chromia, alumina and silica, are used as examples in describing defect structures and transport properties.
169 citations
TL;DR: In this paper, the sulfidation kinetics and mechanism of metals and alloys are compared with oxidation processes, showing the differences from and similarities with oxide systems, and defect and transport properties of metal sulfides are discussed.
Abstract: Defect and transport properties of metal sulfides are discussed, showing the differences from and similarities with oxide systems. The sulfidation kinetics and mechanism of metals and alloys are compared with oxidation processes.
142 citations
References
More filters
1,019 citations
672 citations
TL;DR: In this paper, a study of the effect of Li substitution on the electrical properties of the oxides MnO, CoO, NiO, and CuO has been made.
Abstract: A study of the effect of Li substitution on the electrical properties of the oxides MnO, CoO, NiO, and CuO has been made. It has been found that (1) the activation energy for conduction increases abruptly near the antiferromagnetic Curie point; (2) as Li is added the activation energy and resistivity initially decrease rapidly and then level off in the neighborhood of 2% substituted Li; (3) this initial decrease becomes progressively greater in going from MnO to CuO in the sequence of the periodic table. A rather complete understanding of these materials can be had by treating the conduction process as a thermally activated diffusion of positive holes which are trapped by the local strain induced by their own polarization field. The magnitude of the activation energy will be related to the work done against elastic forces necessary to reduce the local strain at a positive hole to zero.
340 citations