The accurate determination of the concentration of electrons incorporated into cages in 12CaO·7Al2O3 (C12A7) has been examined using iodometry. Preliminary experiments confirmed that iodine is reduced in preference to protons by electron-enriched C12A7, even in aqueous solution. The electron concentrations in several C12A7 samples are measured using a procedure where the iodine molecules in an I2−HCl solution are partially reduced by electrons released from the samples, followed by titration of the residual iodine molecules. The accuracy of this procedure is confirmed by the excellent agreement of the results with those from thermogravimetric analysis. The reevaluated maximum electron mobility is nearly twice as high as that reported previously, and the critical electron concentration for the metal−insulator transition is revised slightly because of the accuracy of the iodometry results.
This chapter reviews gas-sensitive field-effect transistors (FETs) for gas sensing. Although various types of gas sensors have been reported, this review focuses on FET-based sensors such as catalytic-gate FETs, solid electrolyte-based FETs, suspended-gate FETs, and nanomaterial-based FETs. For recognition of analytes in the gas phase, the combination of cross-reactive gas sensor arrays with pattern recognition methods is promising. Crossreactive sensor arrays consist of gas sensors that have broad and differential sensitivity. Signals from the cross-reactive sensor array are processed using pattern recognition methods. Reports of FET-based sensor arrays combined with pattern recognition methods are briefly reviewed.
We develop a theory describing spatiotemporal behavior of spin transport in two-band metals by postulating a spin–exchange interaction between electrons and holes. Starting with the semiclassical Boltzmann equation, we derive a system of coupled diffusion equations and solve them analytically under steady-state conditions. The solutions reveal two types of electron–hole coupled-spin transport modes: a dissipative mode and a nondissipative mode with an infinite spin diffusion length. The two modes are the manifestations of two types of spin coupling channels. Besides the exchange interaction, we incorporate into our derivation the relaxation caused by the spin–orbit interaction to show how it affects the spin transport characteristics of the two modes.
An extended volumetric method, combined with quadrupole
mass spectroscopy
(QMS), is proposed. This method enables us to distinguish and simultaneously
quantify hydride (H–) ions and electrons (e–) incorporated in cages of 12CaO·7Al2O3 (C12A7), which is accomplished upon annealing with
CaH2. When a sample is dissolved in a deuterium chloride
solution, most of the H– ions and electrons released
from cages react to form HD and D2 molecules, respectively.
These isotope-labeled molecules are then detected by QMS. We have
used this method to follow the concentrations of H– ions and electrons in C12A7-treated CaH2 over the thermal
treatment time. We found that during the initial seven days of treatment,
both concentrations increased. Thereafter, the electron concentration
begins to decrease, while the H– ion concentration
continues to increase toward the theoretical maximum. This diverging
behavior is due to differences in their diffusion ratios and thermodynamic
stabilities.
A composite thermionic cathode consisting of 12CaO·7Al2O3 (C12A7) electride and metallic Ti (70:30 vol %) was fabricated as an electron emitter, and the thermionic electron emission properties were evaluated. A high emission current density of ∼1.4 mA cm-2 was achieved at 700 °C with an electric field of 4.0×104 V cm-1. The work function evaluated from the Richardson–Dushman equation was 2.1±0.3 eV, which coincides with the value for pure C12A7 electride and is lower than that for LaB6. Unlike the pure material, the composite has ohmic contact with metallic materials, and can be heated directly by electrical current.
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