Rüdiger Dieckmann

Humidity sensors based on pentacene thin-film transistors

When a pentacene thin-film transistor is exposed to humidity, its saturation current decreases. This decrease was found to be reversible and can therefore be used to measure the amount of relative humidity in atmosphere. The sensitivity was found to depend on the thickness of the pentacene layer. The microscopic origin of the sensing mechanism is discussed.

Cobaltous Oxide Point Defect Structure and Non-Stoichiometry, Electrical Conductivity, Cobalt Tracer Diffusion

The point defect equilibria of cobaltous oxide (Coi_äO) as a function of temperature and oxygen potential are analyzed. Majority point defects are electron holes and differently charged vacancies in the cation sublattice. On the basis of the derived defect model it is possible to quantitatively describe literature data for non-stoichiometry, electrical conductivity and cation tracer diffusion. Additional cation tracer diffusion coefficients were measured at temperatures between 1000 and 1400 °C as a function of the oxygen activity covering the entire 1 atm stability range of this oxide.

Point defects and cation tracer diffusion in (CrxFe1−x)3−δO4 spinels

Abstract The deviation from stoichiometry, δ, in (CrxFe1−x)3−δO4 was measured by thermogravimetry at 1200 °C as a function of oxygen activity, aO2, and cationic composition, x. Moreover, cation tracer diffusion coefficients, D Me ∗ , for Me = Co, Cr, Fe and Mn, were experimentally determined using radioactive isotopes, Co-60, Cr-51, Fe-59 and Mn-54. δ versus log aO2 plots for different x displayed S-shaped curves. The experimental data suggested that cation vacancies and cation interstitials were the majority defects at high and low oxygen activities, respectively. V-shaped curves were observed in D Me ∗ versus log aO2 plots. The observed oxygen activity dependence indicated that the diffusion of Co, Cr, Fe and Mn in (CrxFe1− x)3−δO4 at high oxygen activities is governed by cation vacancies and at low oxygen activities by cation interstitials. Mean cation mobilities were derived by combining non-stoichiometry and cation diffusion information.

Point defects and transport properties of binary and ternary oxides

Abstract Point defects and transport properties of some binary and ternary oxides containing transition metals are discussed on the basis of experimental data on nonstoichiometry, cation tracer diffusion, point defect diffusion, electrical conductivity and on parabolic scale growth. Oxides under consideration are the spinels Fe 3 O 4 , Co 3 O 4 and (Fe, Co) 3 O 4 and the rock salt structure oxides CoO, MnO and (Co, Mg)O.

Point defects and transport in non-stoichiometric oxides: Solved and unsolved problems

Abstract First, the basic concepts used in the area of defects and transport in non-stoichiometric oxides are reviewed. Their capabilities and shortcomings are addressed, including the problems of dealing appropriately with point defects at higher defect concentrations and with situations where more than one sublattice is available for one type of ion. As an example of where ideal solution point defect thermodynamics can be applied without much problems, the iron oxide magnetite, Fe 3 − δ O 4 , is discussed. The cation diffusion in this material is also reviewed. Then some magnetite-based solid solutions are briefly discussed with regard to their defect chemistry and the transport of cations. Finally, two largely ignored topics are addressed: (i) the influence of the valence state of an ion on its diffusivity, (ii) contributions from near-boundary regions to the variation of the oxygen content of non stoichiometric oxides.

The non-stoichiometry and the point defect structure of cuprous oxide (Cu2−δO)

A thermogravimetric study has been performed on the non-stoichiometry of polycrystalline, large-grained cuprous oxide as a function of oxygen activity at temperatures between 800 and 1200°C. The experimental results are analyzed and discussed with regard to the point defect structure of cuprous oxide in combination with literature data on cation diffusion, anion diffusion and electrical conductivity. From the experimental results for the deviation from stoichiometry it is concluded that at least two types of ionic point defects are present as majority defects in Cu2−δO.

Point defects and transport in haematite (Fe2O3-ε)

The point defect structure and related transport properties of the iron oxide haematite, Fe2O3-e are discussed based on data from literature and new electrical conductance and non-stoichiometry dat...

9.6 GHz and 34 GHz electron paramagnetic resonance studies of chromium‐doped forsterite

Chromium‐doped forsterite single crystals grown under conditions that produce a high Cr4+/Cr3+ ratio were examined by electron paramagnetic resonance (EPR) at 9.6 and 34 GHz. The crystals were grown in 2–3 atm of oxygen by the floating‐zone method starting from polycrystalline chromium‐doped forsterite powder synthesized via a sol–gel method. Three crystals with chromium concentrations of 110, 300, and 390 ppm were studied. At 34 GHz, transitions are observed for the laser‐active tetrahedral Cr4+ species that are not observable at 9.6 GHz, which improve the resolution and accuracy with which the magnetic parameters can be measured by EPR. In addition, peaks for a non‐Kramers species appear at 34 GHz that were not observed at 9.6 GHz. These peaks are not analyzed in detail, but are tentatively ascribed to Cr4+ in the octahedral substitution sites of the crystal. At the highest chromium concentration, the Cr3+ spectra show evidence of direct interaction with Cr4+. A global least‐squares fit of the combined ...

Point defects and cation tracer diffusion in (Co, Fe, Mn)3−δO4 spinels: II. Mixed spinels (CoxFezMn2z)3−δO4

Abstract This is the second paper reporting results of systematic studies of the nonstoichiometry and the cation tracer diffusion in quaternary oxide spinels comprised of Co, Fe, and Mn cations. In the first paper, point defects and cation tracer diffusion were discussed for compositions of the type (CoxFe2yMny)3−δO4 (x + 3y = 1). In this study, compositions of the type (CoxFezMn2z)3−δO4 (x + 3z = 1) are considered. The deviation from stoichiometry, δ, has been measured at 1200°C as a function of oxygen activity, aO2, and cationic composition by thermogravimetric measurements. The obtained δ versus log10aO2 curves are basically S-shaped for all cationic compositions investigated. This suggests that two types of point defects, cation vacancies and cation interstitials, are present as majority point defects. Cation tracer diffusion in these spinels has been investigated at 1200°C as a function of oxygen activity and cationic composition by simultaneously using radioactive isotopes, 60Co, 59Fe and 54Mn. Cation tracer diffusion coefficients as a function of oxygen activity in general show a minimum indicating that two types of point defects, cation vacancies and cation interstitials, contribute to the cation tracer diffusion.

Sodium tracer diffusion in an alkaline-earth boroaluminosilicate glass

Abstract Sodium tracer diffusion coefficients, D ∗ Na , have been measured in an alkaline-earth boroaluminosilicate glass in the temperature range 500–800°C by using the radioactive isotope Na-22. It was found that the activation energy of the sodium tracer diffusion changes near the strain point (666°C). Therefore, two Arrhenius-type functions are needed to describe the temperature dependence of D ∗ Na in this temperature range. Below 664°C, D ∗ Na =10 (−2.21±0.07) exp (−(129.9±1.2 kJ/mol) /RT) cm 2 / s and above 664∘C, D ∗ Na =10 (−0.23±0.15) exp (−(165.5±3.0 kJ/mol) /RT) cm 2 / s .