Conduction band of IVa and Va subgroup transition metal monocarbides (I)

Abstract

Abstract Basing on the general conceptions of the band structure of stoichiometric IVa subgroup transition metal monocarbides and assuming two types of atomic interactions a conduction band model for nonstoichiometric carbides has been elaborated which takes into account the vacancies in the carbon sublattice. It is assumed that the formation of vacancies is accompanied by the appearance of local electronic levels in the vicinity of the Fermi level of stoichiometric carbide which, in the case of high concentrations of C‐vacancies, form a subband of unscreened MeMe bonds. This results in a filling of the MeC band, a shift of the Fermi level into the MeMe band, followed by an increase of the electron density of states and an increase of the Fermi level. The increasing density of states leads to an increase in the magnetic susceptibility [17]. On the basis of the above band model, the results of measurements of the Hall effect (in the range 20 to 300° K), thermopower (77 to 300° K), and electric resistivity (77 to 1200° K) of zirconium monocarbide of different composition are discussed. The observed temperature dependence of the Hall coefficient of ZrC x samples indicates that two types of carriers take part in the conduction process, their mutual contribution to this phenomenon changing with the composition of the sample.