Diffusionsvorgänge in festen Stoffen

Häuffe, Karl

doi:10.1007/978-3-642-52680-0_5

Cited by 13 publications

(11 citation statements)

References 148 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The second model explains the sensing effects by changes in the oxygen stoichiometry, that is, by the variation of the amount of the (sub-)surface oxygen vacancies and their ionization (reduction-reoxidation mechanism, Table 1). The origin of both models can be traced back to the 1950s, that is, to the mechanistic description of reactions in and on solid materials; [48,49] since then they have been repeatedly discussed in mechanistic studies (see, for example, references [2,66,87,88]). It must also be kept in mind that the mechanism may be influenced significantly by the materials and operating conditions (e.g.…”

Section: Mechanism Of Gas Detectionmentioning

confidence: 98%

“…[227] From the changes in surface potential and work function, for example, dipole moments of adsorbed molecules were obtained, and conductivity measurements served as a simple and sensitive tool to follow adsorption much more accurately than by direct volumetric measurement. [40] The results of numerous electrical studies over more than 60 years on metal oxides can be found in many reviews and books (see, for example, references [41,43,44,[48][49][50]112] and references therein). In light of these activities, it is remarkable to read recent statements that "there have as yet been no studies on the effect of the conducting or defect properties of the catalysts on their catalytic behavior" [228] and that there is "an urgent need for better knowledge concerning the relation between the conducting properties of the bulk and of the surface region […] to obtain a fuller understanding of the connection between these properties and the catalytic behavior."…”

Section: Mechanism Of Catalytic Reactions: Insights Frommentioning

confidence: 99%

See 1 more Smart Citation

In Situ and Operando Spectroscopy for Assessing Mechanisms of Gas Sensing

2007

View full text Add to dashboard Cite

The mechanistic description of gas sensing on inorganic, organic, and polymeric materials is of great scientific and technological interest. The understanding of surface and bulk reactions responsible for gas-sensing effects will lead to increased selectivity and sensitivity in the chemical determination of gases and thus to the development of better sensors. In recent years, spectroscopic tools have been developed to follow the physicochemical processes taking place in an active sensing element in real time and under operating conditions. Thus, the monitoring of the processes in "living" gas sensors is no longer an unsolvable problem. This Review gives an overview of in situ and operando spectroscopic techniques for the study of gas-sensing mechanisms on solid-state sensors.

show abstract

Section: Mechanism Of Gas Detectionmentioning

confidence: 98%

Section: Mechanism Of Catalytic Reactions: Insights Frommentioning

confidence: 99%

In Situ and Operando Spectroscopy for Assessing Mechanisms of Gas Sensing

2007

View full text Add to dashboard Cite

show abstract

“…This could be analogous to the concentration dependence found later by Meyer-Neldel Hauffe [6] has measured the electrical conductivity of NiO with chromium as a doping agent and, as would be expected from considerations of the electrical neutrality condition and equation ( l ) , found that the electrical conductivity of nickel oxide decreases with additions of chromium while there is a corresponding increase in the parabolic oxidation rate at one atmosphere oxygen pressure. Hauffe [7] and later Hagel [8] also found an increase in conductivity and a decrease in the parabolic oxidation rate for additions of lithium. Schwab and Schmid [9] have studied the effect of added oxides on NiO and found that the trivalent cations Ga, In, and Cr decrease the electrical conductivity and increase the measured activation energy, while the monovalent cations Li, Na, and Ag increase the conductivity and decrease the measured activation energy.…”

Section: Introductionmentioning

confidence: 93%

Electrical Conductivity of Single Crystalline Nickel Oxide

Eror

Wagner

1969

Physica Status Solidi (b)

View full text Add to dashboard Cite

The electrical conductivity of single crystalline NiO was found to be proportional to the 1/4 power of the oxygen pressure for oxygen partial pressures between loo and 10-4 atm over the temperature range of 900 to 1200 "C. These results are in agreement with singly ionized cation vacancies as the predominant nonstoichiometric defect. The sum of the enthalpies of formation of nonstoichiometric disorder and activated enthalpy of movement of an electron hole was found to remain constant when thermodynamic equilibrium was maintained. The activated enthalpy of movement of an electron hole, however, was found to obey the "Meyer-Neldel" relationship, that is, it increased as the concentration of electron holes decreased. An argument has been offered for the explanation of the "Meyer-Neldel" rule. This explanation involves consideration of another equilibrium between free electron holes and those trapped a t imperfections (such as dislocations) which are not usually considered in the usual theory of point defects in nonstoichiometric compounds.Es wurde gefunden, daB die elektrische Leitfahigkeit von einkristallinem NiO im Temperaturbereich von 900 bis 1200 "C fur Sauerstoffpartialdricke zwischen loo und a t exponentiell vom Sauerstoffdruck mit einem Exponenten 1/4 abhlngt. Diese Ergebnisse befinden sich in Ubereinstimmung mit einfach ionisierten Kationenlucken als dominierende nichtstochiometrische Defekte. Es wurde gefunden, daB die Summe der Bildungsenthalpien der nichtstochiometrischen Fehlordnung und der aktivierten Wanderungsenthalpie eines Elektronenlochs konstant bleibt, wenn das thermodynamische Gleichgewicht aufrechterhalten wird. Es wurde jedoch gefunden, daB die aktivierte Wanderungsenthalpie eines Elektronenlochs die ,,Meyer-Ne1delsche"Beziehung befolgt, d.h. sie wachst mit kleiner werdender Konzentration der Elektronenlocher. Eine Erklarung der ,,Meyer-Neldelschen" Regel wird vorgeschlagen, die ein verschiedenes Gleichgewicht zwischen freien Elektronenlochern und denen an Defekten (wie Versetzungen) getrappten berucksichtigt, was gewohnlich in der ublichen Theorie der Punktdefekte in nichtstochiometrischen Verbindungen nicht berucksichtigt wird.

show abstract

“…Karl Hauffe´s Reaktionen in und an festen Stoffen was published in 1955 [17]. The book gave the basics for understanding the structure of oxides and other compounds and their reactions such as oxidation and reduction.…”

Section: Structure Of Oxidesmentioning

confidence: 99%