基础材料和有机材料 (3).pdf

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1、2.2.1 The expression methods of point defectsVMCaNaCaZrNaNaNaNaX()ClClClClX()Theoretically,we can qualitatively and quantitatively treat pointdefects in materials as chemical substances.The generation,equilibrium and concentration of defects can be studied using theprinciples of chemical thermodynam

2、ics.A main symbol to represent the type of defects,superscriptrepresents the effective charge,and subscript represents thelocation of the defects.“.”small black dots represent the positive charge,“丿丿”apostrophe represents the negative charges,and“”representsthe zero charge.The effective charge is eq

3、ual to the existing charge minus thecharge of perfect crystal at the same sites.Each defect can be regarded as a substance,ion vacancy andlattice vacancy are also substance,not nothing.VClrepresents the vacancy of K+.It means that the K+at the original sites was removed,the vacancy has an effective

4、negative charge.VKrepresents the vacancy of chloride ion,which is equivalent to the loss of a chlorine atom and a negative charge at the original sites,so the vacancy has an effective positive charge.Take MX ionic crystal as an example（M2;X2-）（1）VacancyVM:After M atom is removed,the sites occupied b

5、y M atomforms vacancy.VXrepresents the position occupied by the X atom formsvacancy after the X atom is removedVNa VeVNaNarepresentThe vacancy of chloride ion,which is equivalent to the lossof a chlorine atom and a negative charge at the original sites.So theres an electron hole in the vacancy.VhVCl

6、ClThe ionic compound is regarded as completely composed ofions(chemical bond properties are not considered here),forNaCl crystal,removing the Na+at the normal sites will producea cation vacancy with an effective negative charge.(2)Interstitial atoms:Interval is represented by i.Mirepresents M atom e

7、nters the interstitial sites.when the X atomenters interstitial sites,it is represented by Xi.(3)Misplaced position(misplaced atom)MXrefers to M atom misplaces the equilibrium position ofnormal X atom.It does not mean that the positive ion occupies theposition of negative ion.CaNa（6）Charge defectsVV

8、V VNaClNaCl ()(7)Association center refers to the association of point defectswith opposite charges through coulombic forces.For example：in NaCl crystal.The substitution of different valence ions.For example,Ca2+displaces Na+,and bivalent substitution one with a positivecharge.In the same way,the replacement of Zr4+by Ca2+has twonegative charges.