Papers by Keyword: Vacancy Formation Energy

Abstract: We investigated the relationship of the vacancy formation energy with kinematic viscosity and self-diffusion coefficient in liquid metals at the melting temperature. Formulas are obtained that relate experimental values of the vacancy formation energy, kinematic viscosity, and self-diffusion coefficient to the atomic size and mass, the melting and Debye temperatures. The viscosity and self-diffusion parameters are introduced. The ratio of these parameters to vacancy formation energy is equal to dimensionless constants. It is shown that the formulas for viscosity and self-diffusion differ only in dimensionless constants; the values of these constants are calculated. Linear regression analysis was carried out and formulas with the highest adjusted coefficient of determination were identified. The calculated values of the self-diffusion coefficient for a large number of liquid metals are presented.

Abstract: In this work, we investigated and discussed the experimental and theoretical data of the vacancy formation energy E_v. The results of calculations in the continuum model of the solids and the model of interaction between a pair of neutral atoms, as well as the results of ab initio methods using various exchange – correlation functionals, are analyzed. It was found that the experimental and theoretical values of the vacancy formation energy have an adjusted coefficient of determination R² close to 0.80. The relationship between the calculated vacancy formation energy and the sublimation enthalpy most closely corresponds to the relation E_v = ΔH_s/3 for the results obtained on the basis of continuum model and model of interaction between a pair of atoms. The vacancy formation energy most closely correlates with the melting enthalpy ΔH_m. The adjusting coefficient of determination R² of this relation is 0.87 in comparison with 0.71 and 0.84 for the sublimation enthalpy and the evaporation enthalpy, respectively.

Abstract: Late Professor Stewart initiated and shaped the International Conference on Positron Annihilation (ICPA) series. As a first-generation experimental positron-annihilation scientist, he made full use of the angular correlation of annihilation radiation (ACAR) method. He applied this method to study Fermi surfaces of metals, positron wave-functions in crystals, positron-electron and -phonon many-body interactions, and the vacancy formation energy in solids. He also studied with this method positronium in liquids and solids (T. Hyodo, J. Phys. Conf. Series, 618 (2015) 012002). All these studies enjoyed by Professor Stewart will long be remembered by the positron study community.

Abstract: The ab inttio density functional theory had been used to calculate the vacancy formation energy of C in the vanadium carbide, to reveal the effects of super-cell size and parameters k points. It turned out that,the calculation model of C vacancy formation energy in VC should be contain 64 atoms, while the K grid meshed 5x5x5 above using the Monkhorst-Pack method. And due to the vacancy formation energy of C 6.76eV, the high vacancy concentration of VC could be caused by simple thermal vibration. These researches not only had a certain value to know VC properties, but also had great significance to rediscover the forming of vacancy.

Abstract: Vacancies of the crystal is one of the core issues in solid physics, solid state chemistry, metallurgy and materials science. In this paper, we present the latest research on the vacancy formation energy and size dependence of vacancy formation energy. According to the vacancy formation energy of common methods and common description of the vacancy formation energy theory, the vcancy formation energy characterization, calculation and simulation methods are described; the nature and origin of the vacancy in nanoscale is analyzed. finally, further research will focus on the properties mechanisms of the other physical properties, mechanical properties and thermodynamic in materials.

Abstract: A model for size dependent vacancy formation energy of nanosolids (nanoparticles, nanowires and nanofilms) has been developed by the consideration of their surface free energy. It is found that the vacancy formation energy of nanosolids decreases with the decrease of size. The relative variation of vacancy formation energy of nanoparticles, nanowires and nanofilms to bulk value at specified size follows 3:2:1. Furthermore, vacancy formation energy of nanosolids changes linearly with the reciprocal of size. The present results agree well with the predictions of BOLS and ECN theory.

Abstract: Al alloys with Mg as the major alloying element constitute a group of non-heat treatable alloys with medium strength, high ductility, excellent corrosion resistance and weldability. However, the segregation of Mg may adversely affect the performance of these materials if they are exposed to rapid heating and cooling environments such as resistance spot welding. The formation and migration of vacancy is an important factor affecting Mg segregation. In this paper, the amount and distribution of Mg were measured by electron probe microanalysis and the vacancy formation energy in AA5754 alloys was measured by positron annihilation lifetime spectroscopy. The results indicated that the segregation of Mg at cracks, occurring under suitable temperature and stress conditions, is related to the formation and migration of vacancies, and may promote crack initiation and propagation.