Refractories electron transport

OA Golikova. Electron transport in boron-rich solids. In D Emin, TL Aselage, C Wood, eds. Novel Refractory Semiconductors. MRS Symposia Proceedings 97 17, 1987. 

The electrical characteristics of ceramic materials vary gteady, since the atomic processes ate different for the various conduction modes. The transport of current may be because of the motion of electrons, electron holes, or ions. Electrical ceramics ate commonly used in special situations where reftactoriness or chemical resistance ate needed, or where other environmental effects ate severe (see Refractories). Thus it is also important to understand the effects of temperature, chemical additives, gas-phase equilibration, and interfacial reactions. 

A probable mechanism of the refractory compounds synthesis is discussed. Hypothetical schemes of the carbon, boron and silicon transport in ionic-electronic melts are proposed. 

It is for the first time hypothesised that boron and silicon are present in ionic-electronic melts in the form of anions. The role played by these anions in the transport reactions involved in the synthesis of the refractory compounds is discussed. 

Nikiforov, I. Ya. Kolpachev, A. B. (1988). Phys. Status Solidi (b) 148, 205. Nikitin, V. P. (1982). The influence of structural defects, metallic and metalloid substitutions on the electronic structure and transport properties of refractory carbides. Doctor of Philosophy Thesis, Institute of Metal Physics, Kiev. 

This review deals mainly with the electrical and thermal conductivities at temperatures T from 0 K to room temperature. It is the region where the lattice vibrations must be described by quantum mechanics, and the phonon spectrum determines much of the temperature dependence of the transport properties. The absolute magnitudes of the electrical and thermal conductivties depend crucially on a consideration of the quantum mechanical matrix elements for the scattering of electrons and phonons. They are difficult to calculate, not only for the refractory systems of interest here but for most solids. Theories of conduction properties therefore contain parameters, some of which are fairly well known while others are quite uncertain. 

There are few measurements of the thermal conductivity of refractory compounds. Williams et al. (24) measured k(T) in TiB2. Radosevich and Williams (25) [see also Williams (26)] measured k in normal and superconducting NbC. In a conventional superconductor, the thermal conductivity decreases on the transition to the superconducting state. The reason is that the electrons in the superconductor cannot transport heat because they would fall into the forbidden energy gap if they lost energy. (A superconductor is not a thermal superconductor, and the Wiedemann-Franz law is not valid.) Contrary to this behavior, Ktot in NbC increased as one passed below T. This can be understood from the dominating role of Kia, which is limited by Tpi,.ei. In the superconducting NbC the phonon-electron interaction becomes weaker and hence Kiat increases. 

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