Study On Point Defects Of Transition Metals

Crystal defects include vacancies, interstitials, dislocations and grain boundaries,which are significant for metals and alloys. The defects influence the physical andmechanical properties of materials. They enhance the solid solution to improve thestrength of materials, as well as effect on the aging and diffusion by diffusion. Thepoint defects can transform into other kinds of defects when thousands of themgenerate in the crystal such as dislocation, stacking faults, and so on. Studying theproperties of vacancies and interstitials is meaningful, which is necessary forunderstanding the thermodynamic and kinetic behavior of materials and alloys. Wediscuss vacancy formation energy, interstitial formation energy and also bindingenergy by the first principle.In the thesis, we have studied V Cr Fe Nb Mo W in bcc transition metals andNi Rh Pd Cu、Ag in fcc transition metals and calculated their vacancy formationenergy, interstitial formation energy and also binding energy. Form the discussion wehave got the conclusions like these:(1) The binding energy, which is calculated by method of Generalized GradientApproximation (GGA) of PBE, is larger than published experimental results becausewe calculated the energy of isolated atom from the super-cell which contains sixteenor thirty-tow atoms. The vacancy formation energy agrees with other theoreticalcalculations.(2) The energy of <110> or <111> dumbbell configuration in bcc is the smallest,so <110> or <111> dumbbell configuration is stable. In the fcc,<111> dumbbell oroctahedral coordination is the most stable.(3) The ratio ofE vtoEc is1/2-1/4approximately. IfE cincreases, so doesE v.(4) The relationship ofEi and B is that as B increases,Ei also increases.