Lattice Dynamical Studies of Transition Metal Carbides
Başlık:
Lattice Dynamical Studies of Transition Metal Carbides
Yazar:
Singh, Ajay Kumar, author.
ISBN:
9780355897692
Yazar Ek Girişi:
Fiziksel Tanımlama:
1 electronic resource (170 pages)
Genel Not:
Source: Dissertation Abstracts International, Volume: 79-10(E), Section: B.
Özet:
The present thesis is an outcome of the efforts devoted to carry out a systematic theoretical investigation of the lattice dynamics of Transition Metal Carbides (TMC) of rocksalt structure. This is self evident from the fact that the experimental elastic constants obey the strange relations C 44 ≈ 2C12 for all carbides. Also, it is seen that (C 12-C44) ≤ 1.0 for almost all TMC except for NbC (C 12-C44) is +nue. Also these carbides show degeneracy at the zone center vibration frequencies ie, there is no LST splitting at the zone center (Gamma point), which is not absent in alkali halides.
Quantum mechanical calculation of the cohesive energy of ionic crystals leads in addition to a two-body potential, to a many-body interaction potential also. This interaction potential owes its origin to the non-orthogonality of the free-ion one-electron wave functions arising from the deformation of electron shells between the neighbouring ions. In case of alkali halides, it has been shown by Lowdin and Lundqvist that 5 to 10 percent of the cohesive energy can be ascribed to many-body interactions. This interaction energy consists of several terms of successively decreasing order of magnitude. The first important term of this series is the three-body component which gives a simple and logical explanation of the deviations from the Cauchy relation C12=C44 observed in the case of crystals. The form of this component is such that the force due to mutual displacement of the two ions remains radial but its magnitude depends on the displacement of a third ion. The contribution of these interactions to the dynamical matrix has Been evaluated for ionic crystals with NaCl-Structure by Verma and Singh.
Notlar:
School code: 1918
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Yer Numarası | Demirbaş Numarası | Shelf Location | Lokasyon / Statüsü / İade Tarihi |
---|---|---|---|
XX(683265.1) | 683265-1001 | Proquest E-Tez Koleksiyonu | Arıyor... |
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