Papers by Keyword: Vacancy Concentration

Abstract: The study of formation energy and the vibrational effect on the vacancy concentration in the gray tin (α-Sn) using density functional theory has been successfully carried out. The vacancy is modeled by using a supercell consisting of 64 atoms. The vibrational effect is obtained by calculating the phonon density of states (P-DOS) of perfect and vacancy gray tin through the Gaussian-function approach. It is found that the formation energy of Sn-vacancy is 1.89 eV, and the vacancy concentration at the melting point is 3.68 × 10³ cm^-3. However, the vacancy concentration increases significantly to 6.48 × 10⁹ cm^-3 when the vibrational effect is considered. It is expected due to the softening of P-DOS on the vacancy case.

Abstract: Alloys of the Fe-Al system are interesting due to occurrence of long-range order and many thermal vacancies at high temperature, which lead to not only significant hardening, but also cause changes of physical properties. High temperature diffusion is conditioned by structural defects in solids, such as vacancies, foreign atoms and dislocations influencing thermal characteristics of a solid solution, among others the thermal diffusivity coefficient. Measurement of thermal diffusivity was performed at room temperature using the laser flash method. For characterization of the defect structure, positron annihilation lifetime spectroscopy was used. The data were presented for alloys with 28 and 38 at.% aluminium without chromium and containing 5 at. % Cr addition. The results showed that thermal diffusivity decreased with aluminium content and deviation from stoichiometry. In the studies, different structural defects in the alloys were observed.

Abstract: Using the peculiar behavior of nitrogen molecules in FZ silicon crystals contained with a high concentration of vacancies, this paper describes the following four important values: the estimated vacancy concentrations, the deep levels at 0.44 eV under the conduction band for n-type and at 0.66 eV over the valence band for p-type for mono vacancies and the diffusion coefficient of the silicon interstitials DI-FZ = 1.3×exp(-4.5 eV/kT).

Abstract: The effect of Si additions on vacancy behavior following solution treatment and quenching was studied for an Al-Cu-Mg-Ag alloy system using positron annihilation lifetime spectroscopy (PALS). Both the initial positron lifetime and steady state positron lifetime increase as the Si concentration increases. This behavior is interpreted in terms of Si interacting with vacancies, leading to their retention in the alloy. The ability of PALS to monitor vacancy behavior after solution treatment should allow the improved prediction of phase transformation kinetics and hence the tailoring of ageing treatments.