基础材料和有机材料 (2).pdf

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1、ContentsDefects in Crystalline Solids1.The classification of point defects.2.Rules for writing defect reactions.3.The calculation of defect concentration,4.Non-stoichiometric compounds.2.1 Types of point defects1.The cause of defects：thermal vibration of the particles,impurities,the change of atmosp

2、here.2.Ideal crystal:a crystal whose particles are arranged in strictaccordance with a spatial lattice.3.Real crystals:crystals with various structural imperfections.4.crystal defects refer to the imperfection of real crystal whichdeviates from ideal crystal.The importance of research defects：conduc

3、tive,semiconductor,chromogenic(color center),luminescence,diffusion,sintering,solidstate reaction(basis of Materials Science).of planesdistortion Vacancyof planesdistortion interstitialself-Figure 2.1Figure 2.2The classification of point defects.According to the geometric position of the real crysta

4、l deviated from the ideal crystalVacancy:The normal lattice sites is not occupied by the particles.Interstitial atomsThe constituent particles occupy interstitial sites in crystal.Impurity atomsForeign atoms enters the lattice,which may be mixed in thecrystallization process,or added on purpose.Two

5、typesInterstitial position:interstitial impurity atomsNormal lattice sites:substitute impurity atomssolid solutionsInterstitial solid solutions solvent atom solute atom solvent atom solute atom substitutional solid solutions Thermal defectsImpurity defects Non-stoichiometric structural defectsAccord

6、ing to the causes of point defects A:Frenkel defectsFigure 2.3 Frenkel defects1)Thermal defects refer to a part of atoms with larger energyin the lattice will leave the equilibrium position via thermalmotion when the temperature of crystal is higher than 0 K.ZnZnVZniZnFrenkel defectsVacancy and inte

7、rstitial are produced in pairs,and the volume and density of crystal does not change.For example:ZnO crystal with wurtzite structure,Zn2+can leavethe original sites and enter the gap.From the viewpoint of energyFigure 2.4 Schottky defectsB:Schottky defectsNaClVVNaCl Formation：It is basically a vacan

8、cy defect,the particles moveto the surface of crystal through thermal motion,and formvacancy in the original position.Characteristic:the positive and negative ion vacancies areproduced in pairs.Schottky defect decreases the density of thesubstance.Analyze from the viewpoint of energy.The energy of f

9、ormingSchottky defect is relatively low,so Schottky defect is usuallythe main defect.Impurity defects：A defect caused by the entry of impurityatoms into a crystal.The number of atoms entering the crystal isgenerally less than 0.1%.Types：interstitial impuritysubstitutional impurityCharacteristic：The

10、concentration of thermal defects is relatedto temperature,while the concentration of impurity defectsdepends on the solubility and doping amount of impurities.Reasons for existence：It may be stem from its own existenceor added purposefully to improve some properties of the crystal.3)Non-stoichiometr

11、ic defectsThe structural defects existing in the non-stoichiometriccompound.The constituent elements are in non-stoichiometricratio due to defects.The chemical composition of materials isrelated to the surrounding environment and atmosphere.Suchas TiO2-xA non-stoichiometric defects is essentially a kind of chargedefect.