Electronic States in Liquid and Amorphous Metals.
This thesis deals with the calculation of the electronic spectrum of close-packed structurally disordered systems such as liquid and amorphous metals. Because of their potential in technology, metallic glasses are of considerable current interest both experimentally and theoretically. The key to understanding many of their physical properties is their electronic structure. We limit ourselves to the consideration of electron states in the one-electron approximation and to systems in which at least one atomic species is a noble or transition metal. Here the d-electrons undergo resonant scattering and the average spectrum cannot be described in terms of finite order perturbation theory. We apply the Effective Medium Approximation (EMA) to systems having a muffin-tin Hamiltonian. The systems that we study are molten Cu and Ni-P and Ni-B alloys. We calculate the densities of states and the resistivities of liquid Cu at two different temperatures. We also show that the random-number based annealing techniques of statistical physics can be used to obtain two site distribution functions that are suitable for use in our model. We calculate the complete electronic spectra of Ni-P and Ni-B alloys. We constructed self-consistent muffin-tin potentials as input parameters for these calculations. Our first-principle calculations predict reasonable values for the negative temperature coefficient of the resistivity for liquid Cu (for the appropriate range of Fermi energies) and thus provide support for the Faber -Ziman semiempirical model. Our results for the alloy calculations are discussed in the light of the Nagel-Tauc model regarding electronic contributions to the reltive stability of metallic glasses. We conclude that the Nagel-Tauc model is not appropriate for transition metal-metalloid alloys though their ideas may be relevant for noble metal-metalloid systems. In the future, as the required structural data becomes available for a wider range of alloy systems, EMA calculations will play an increasingly important role in understanding the electronic properties of metallic glasses.
- Pub Date:
- Physics: Electricity and Magnetism; Engineering: Metallurgy