The Characterization And Caculation Of Vacancy

Vacancy is a simplest and ordinary defect in solid, and many physical and mechanic properity of solid relate with vacancy. Studying the formation of vacancy and its properity at length is very important to material microstructure and macrostructure properity. Vacancy has a great influence on the structure evolution of materials, such as phase transformation and atomic diffusion, as well as some mechanics behaviors. However, it is difficult to observe and characterize vacancy as yet. There hasn't been a effective experiment method to characterize vacancy in the crystal lattice. By using positron annihilation technique and Mossbauer method, we can only survey the surface vacancy density. By using atomic force microscope, only the vacancy of sample surface can be observed. How to probe vacancy in crystal interior directly and observe its morphological property is attractive. Thus, the characterization of vacancy is increasely meeting the need for the science research field.In this paper the diffraction intensity of crystal containing vacancy was studied by using the scattering matrix method. The diffraction intensity of containing vacancy crystal and the perfect crystal was caculated by the diffraction dynamics formula which derivated from the containing crystal. Then the ratio between them was transformated into contrast and the luminosity-grey scale comparison picture of atom-vacancy was simulated. the microstructure was studied by TEM and its pictures were made into HRTEM microimage by using the Digital Micrograhy soft. The HRTEM microimage was analysied and compared with the grey scale picture of atomic-vacancy.By using diffraction dynamics of containing vacancy crystal, binding the grey scale picture of atom-vacancy and atomtic microstrcture of HTEM, the vacancy of nanocrystalline materials was characterized in this paper.A new method was put forward to calculate the vacancy formation energy. Based on the model proposed by Tiwari and Patil, we have improved the calculation method for surface energy, and calculated the vacancy formation energy for typical metals, such as fcc, bcc and hcp metals. It is found that calculated results and the experimental values are agreement with each other by introducing a energy modified coefficient, the new method proposed by us can calculate and predict the vacancy formation energy efficiently. The calculation method of vacancy formation energy for nanostructure metals is also studied by introducing figure factor and considering grain size effect, The results show that the vacancy formation energy of nanostructure metals decreases with the reducing the grain size and the vacancy formation energy decreases linearly with increasing the figure factor.