The aim of this study is to clarify the relation between microstructure and properties (hardness and electrical resistivity) of copper wire drawing by the ENICAB Company and distended for electrical cabling. In this work we studied the evolution of the microstructure and (mechanical/electrical) properties of the wire drawn and annealed at 260°C. The drawing causes structural anisotropy that results in an elongation of grains along the axis of drawing. There was also an increase in electrical resistivity and in hardness following the deformation level increases. After annealing at 260C of the drawn wire, it was found a gradual return of the mechanical properties and microstructure to a state close to the state of as-received copper.
We theoretically study possible domain-type collective dimerizations of graphite induced by inter-layer charge transfer excitations in the visible region. Using the semiempirical Brenner theory, we have calculated the adiabatic energy along the path that starts from original two distant graphite layers, but finally reaches the dimerized domain which consists of about 100 carbons with inter-layer σ-bonds. The energy barrier between this new domain and the starting graphite is shown to be of the order of 1 eV, being easily overcome by applying a few visible photons. We have also shown the optimal path of transformation via step by step increase of the domain size.
Recent experiments indicate that a photostimulated graphite with a femtosecond laser pulse results in the formation of a stable domain with sp^3 like interlayer bonds. By means of the energy barrier minimization and molecular dynamics using the empirical Brenner potential we study a geometrical structure of the new phase. We clarify proliferation of the initial domain and prove that the overall process is a multiphoton one. Furthermore, we present a model describing the initial transformation - an interlayer charge transfer resulting in the localization of an exciton-like state. The local density approximation electronic structure analysis reveals that the electronic state of the new phase is an insulator immersed in semimetal. We study by means of the long-range carbon bond order potential the effect of the existence of the new phase on the surrounding graphite and propose a new mid step structure on the path of a photoinduced graphite-diamond conversion.
The results of synthesis, crystal structure characterization and luminescence properties study of the Pr³⁺-doped bismuth orthophosphate, BiPO₄, polycrystals are reported. It was found that doping of bismuth orthophosphate with praseodymium of concentration more than 1% leads to phase transition of BiPO₄ from so-called "high-temperature monoclinic" to "low-temperature monoclinic" structure. At room temperature studied samples revealed intensive red luminescence caused by radiation electronic transitions in the Pr³⁺ ions under their intrinsic f → f excitation at ³H₄→ ³P₁+¹I₆ absorption transition. Influence of phase transformation as well as multi-phonon and cross-relaxation processes on the luminescence of the Pr³⁺-doped BiPO₄ compounds were discussed.
Thin films of TiO_{2}-SnO_{2} and SrTiO_{3}-BaTiO_{3} are deposited by rf sputtering. The crystallographic and optical properties near the band gap absorption are investigated as a function of film composition. Systematic displacement of the fundamental absorption edge shows different behaviour for amorphous and polycrystalline samples. Results are discussed in terms of the influence of the substitution on the local environment of Ti ion and Me-O distances. Application of XANES and EXAFS is proposed for the studies of solid-state solutions.
The experimental investigations of "order-order" kinetics in Ni_{3} Al-based L1_{2}-ordered intermetallic compounds revealed the relaxation curves composed of two parallel processes considerably differing in relaxation rates. A simple Ising-type model based on a vacancy mechanism of atomic jumps was used to carry the Monte Carlo simulations of long-range-order relaxations in a binary A_{3}B system with L1_{2}-type superstructure. The simulated relaxation curves fitted weighted sums of two exponentials with significantly different relaxation times. It was found out that the fast relaxation process is controlled by the dynamics of the minority B-atom jumps.
The paper discusses a theoretical model that associates the shape of Mössbauer spectrum with the configuration of atoms in local surroundings of the Mössbauer nuclide. The model has been implemented to a computer program which was used to analyse the Mössbauer spectra of Fe_{72}Al_{28} alloys after various heat treatments. Basing on the determined configuration of atoms, the long range ordering parameter was estimated.
Some most representative results for semicrystalline polymers by positron annihilation spectroscopy method, showing the influence of crystallinity and morphology of samples on positron annihilation characteristics, are reminded. The latest finding of the author's experiment on modified polyamide 6 is presented. The latter reveals that the interfacial zone between a lamella and an amorphous region may influence the ortho-positronium characteristics. The role of chain defects is stressed.
Multicomponent single phase alloys were synthesized according to the idea of iron-average atom system. X-ray diffraction shows formation of bcc phase and traces of unidentified phase. Mössbauer spectra indicate presence of two components with different hyperfine magnetic field distributions. The high field component corresponds to the majority ferromagnetic phase. Few per cent of iron builds low field component. The dominant effect of annealing consists in an increase of the low field component.
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