固体物理683995

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1、2.2.4ScatteredWaveAmplitudeandStructureFactor(p.39)'(18)FdVn(r)expikkrdVn(r)expikrcrystalWhenthediffractionconditionissatisfied,i.e.kG(21)Eq.(18)canbewrittenasFdVn(r)expiGrGcrystalNdVn(r)expiGrNS(39)GcellNcellsr=0atavertexofthecellSdVn(r)expiG

2、rGcellStructureFactorRevisionSupposingjatomsinthecell,totalelectronconcentrationatduetoallatomsinthesinglecell:rn(r)nj(rrj)(40)jSdVn(r)expiGrGcelldVnj(rrj)expiGrjexpiGrjdVnj(rrj)expiG(rrj)(41)jatomPhasefactorbetweenatomsWedefinetheatomicformfactor

3、fdVn(rr)expiG(rr)jjjj(42)atomSothatSGfjexpiGrj(43)jStructureFactorRevisionScatteringintensityAtomsinacellrjxja1yja2zja3(44)Foragivenscatteringn1,n2,n3:G1b12b23b3SfexpiGrGjjj(46)S()fexpi2(xyz)G123j1j2j3jjIntensityofthescatteringforG22*I

4、FSSSGGGGGFromknownf,obtainatomarrangementinacrystalcelljAccordingtotheknowncrystalstructure,deducetheintensityforacertaindiffractionExample:structurefactorofabcclattice(p.40)-Twoatomsinthecrystalcellwithcoordinates(000)and(½,½,½)-Thetypeofatomsisthesame,andtheatomicformfactorisf-Forac

5、ertaindiffractionvectorGbbb112233StructurefactorS()fexpi2(xyz)123j1j2j3jjffexpi()123f1expi()123When=oddinteger,123S(123)0=eveninteger,S()2f123123Inadiffractionpatternofabcccrystal,-(100),(300),(111),(221)etc.donotappear.-(200),(110),(2

6、22),etc.arepresent.Figure2-16Explanationoftheabsenceofa(100)reflectionfromabcclattice.MITOpenCourseWareStructurefactorinCsClstructure-Twoatomsinthecrystalcellwithcoordinates(000)and(½,½,½)-Twotypesofatomswiththeatomicformfactorsfandfrespectively1222IFSGGGffexpi()ffexpi()

7、121231212322ff2ffcos()1212123Iff~f,when=oddinteger,I~012123Fig.2-17ComparisonofX-rayreflectionsfromKClandKBrpowders2.2.5AtomicScatteringFactor(p.41)WedefinetheatomicformfactorfdVn(rr)exp