Lattice dynamics in Hydrogenated Austenitic Stainless Steels and in the Superionic Conductor Cu 2-δ Se

The objects of research are lattice dynamics in fcc systems; austenitic stainless steels, hydrogenated austenitic stainless steels and superionic conductor Cu2-δSe. The thesis can be divided into three parts: modelling of lattice dynamics in austenitic stainless steels with different composition; modelling of optic modes of hydrogen vibrations in austenitic stainless steels with variation in alloying composition and hydrogen contents; investigation of structure and lattice dynamics of copper selenide Cu2-δSe compounds with different compositions. Firstly were investigated non-hydrogenated austenitic stainless steels. The experimental data phonon dispersion curves for the steels Fe-18Cr-12Ni-2Mo and Fe-18Cr-16Ni-10Mn are very similar. The Born-von-Karman model calculation together with the generalized force matrices (5 neighbouring shells) fits well to the experimental data. Using the Born-von Karman model with only two neighbouring shells and introducing the electron gas contribution instead, a significant improvement of the fit can be achieved. With this approach a satisfactory fitting with only few fitting parameters was obtained. In the further work INS study was performed on hydrogenated austenitic stainless steels. The experimental data for inelastic neutron scattering in highly hydrogenated austenitic stainless steels show significantly different results from the samples with medium and low hydrogen content. The fully hydrogenated samples have obviously a two peak structure due to the hydrogen-hydrogen interaction. In this system is used Born-von-Karman model(2 neighbour shell). In the samples with medium and low hydrogen content only one non-symmetric peak exists. Dominant term in this samples is due to influence of different alloying elements. The model which fit experimental data well is model of Einstein oscillators. The structure in α-copper selenide is determined as a function of composition . In Cu1.75Se, Cu1.78Se and Cu1.8Se at room temperature the cations occupy tetrahedral and octahedral interstices within the fcc anion sublattice. In Cu1.85Se and Cu2Se at elevated temperature no octahedral occupation has been detected, although considerable copper density is localised near the tetrahedral-octahedral boundary. The phase diagram of the system Cu-Se is not completely determined yet, especially on the low and high temperature regions. Diffraction studies gave indication that exsolution of copper in copper selenide occurs