ch1 点缺陷.ppt

Defects 晶体的结构缺陷 总 述 1、缺陷产生的原因——热震动 杂质 2、 缺陷定义——实际晶体与理想晶体相比有一定程度的偏离或不完美性， 把两种结构发生偏离的区域叫缺陷。 3、研究缺陷的意义——导电、半导体、发色（色心）、发光、扩散、烧结、固相反应………。（材料科学的基础） 4、缺陷分类——点缺陷、线缺陷、面缺陷 It is useful to think about solids in terms of a regular repeating pattern of planes of particles. But it is important to recognize that solids are seldom perfectly ordered. There are four basic mechanisms for introducing a point defect into the structure of a solid. When a particle is missing at one or more lattice sites we get a vacancy. When a particle forces its way into a hole between lattice sites, we get an interstitial impurity. Substitutional impurities result from replacing the particle that should occupy a lattice site with a different particle, such as substituting a K+ ion for a Na+ ion in NaCl. (If an ion with a different charge is substituted, the electrical neutrality of the crystal must be maintained. If a Ca2+ ion is substituted for a Na+ ion, for example, a second Na+ ion must leave the crystal so that it doesnt pick up an electric charge.) Ch1 Points defects The one dimensional defect is called a point defect, implying that it involves only one atom surrounded by an otherwise perfect lattice. However, the presence of a point defect may affect the properties of its nearest neighbors, and by elastic interactions, a sizable spherical region of the lattice around the defect. Ch1 Points defects 点缺陷的概念 点缺陷对材料性能的影响 点缺陷的概念 一、类型 A 根据对理想晶体偏离的几何位置来分，有三类 Ch1 Points defects 1.1 空位及间隙原子的几何组态 1.2 点缺陷的形成能 1.3 点缺陷的热平衡浓度 1.4 点缺陷的运动 Classification of Point defects Two point defects are intrinsic to the material, meaning that they form spontaneously in the lattice without any external intervention. These two are the vacancy and the self-interstitial, shown schematically in a 2-D representation in the following Fig. The vacancy is simply an atom missing from a lattice site,which would be occupied in a perfect lattice. The self-interstitial is an ato