Electronic Structure of Refractory Carbides and Nitrides by V. A. Gubanov

By V. A. Gubanov

This e-book provides a scientific description of the digital and physico-chemical houses of transition steel carbides and nitrides. The dialogue is dedicated to the theoretical modeling of refractory carbides and nitrides and alloys according to them, and the authors uniquely utilize computational tips on how to calculate their spectroscopic, electrical, magnetic, superconducting, thermodynamical, and mechanical houses.

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Electronic Structure of Refractory Carbides and Nitrides

This ebook provides a scientific description of the digital and physico-chemical homes of transition steel carbides and nitrides. The dialogue is dedicated to the theoretical modeling of refractory carbides and nitrides and alloys in accordance with them, and the authors uniquely utilize computational easy methods to calculate their spectroscopic, electrical, magnetic, superconducting, thermodynamical, and mechanical houses.

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4 1 \ 1 \ r> ^ 0 Fig. 19 Total DOSs for (a) YbC 2 and (b) YbN. 19 Ry. 24 Ry. 314 Ry) and, as a consequence, the two-valence state of Yb is the most stable one. 548 Ry) exceeds the promotion energy, and the more stable configuration is Yb 3 + . The formation of C-C chemical bonds in a variety of solids, including some refractory dicarbides, has been considered by Li and Hoffman (1989) and Wijeyesekera and Hoffman (1984) based on EHT (extended Huckel theory) calculations. To our knowledge, these works are the only ones where the band analogues of bond populations, the so-called crystal orbital overlap populations (COOPs) have been calculated for refractory compounds.

According to their investigations, Pd-C bonding is formed due to the hybridisation of the Pd4d, Pd5s and C2p states. An empirical energy diagram of the valence states in hexagonal ReC (y'-MoC crystal structure) was proposed by Zhurakovsky, Zaulichny and Khitun (1988) based on XES and X-ray electron spectroscopy data. An appreciable hybridisation of the Re5d- and C2p-orbitals in the valence band of the carbide was proposed. 3 Bond populations for the clusters in MnxCy carbides. 183 CKa and ReL3 absorption spectra, together with the measured values of the core Re4/, Cls binding energies led the authors to the conclusion that charge density is shifted from metal atoms to the intersphere region of hybridised states.

The Fermi surface topology in refractory carbides has also been studied in detail. The Fermi surface in TiC was first calculated by the linear combination of atomic orbitals (LCAO) method (Ern and Switendick, 1965) and then by the KKR method (Schadler, Weinberger, Klima and Neckel, 1984). It was shown that the largest sheets of the Fermi surface are hole-like in character. This contradicts the results of Hall coefficient measurements for TiC (Bittner and Goretzki, 1960; Dubrovskaya, Borukhovich and Nazarova, 1971), which clearly show the electronic character of conductivity.

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