最新X-Ray Diffraction - iitk.ac.in教学讲义ppt课件.ppt

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1、X-RayDiffraction-iitk.ac.inHowtoproducemonochromaticX-rays?HowdoesacrystalscattertheseX-raystogiveadiffractionpattern?Bragg’sequationWhatdeterminesthepositionoftheXRDpeaks?Answer)thelattice.WhatdeterminestheintensityoftheXRDpeaks?Answer)themotif.Howtoanalyzeapowderpatterntogetinformationab

2、outthelatticetype?(Cubiccrystaltypes).WhatotherusescanXRDbeputtoapartfromcrystalstructuredetermination?GrainsizedeterminationStraininthematerial…Whatwillyoulearninthis‘sub-chapter’?Forelectromagneticradiationtobediffracted*thespacinginthegrating(~aseriesofobstaclesoraseriesofscatterers)shoul

3、dbeofthesameorderasthewavelength.Incrystalsthetypicalinteratomicspacing~2-3Å**sothesuitableradiationforthediffractionstudyofcrystalsisX-rays.Hence,X-raysareusedfortheinvestigationofcrystalstructures.NeutronsandElectronsarealsousedfordiffractionstudiesfrommaterials.Neutrondiffractionisespecial

4、lyusefulforstudyingthemagneticorderinginmaterials.SomeBasics**LatticeparameterofCu(aCu)=3.61ÅdhklisequaltoaCuorlessthanthat(e.g.d111=aCu/3=2.08Å)**Ifthewavelengthisoftheorderofthelatticespacing,thendiffractioneffectswillbeprominent.ClickheretoknowmoreaboutthisAbsorption(Heat)IncidentX-raysSP

5、ECIMENTransmittedbeamFluorescentX-raysElectronsComptonrecoilPhotoelectronsScatteredX-raysCoherentFromboundchargesX-rayscanalsoberefracted(refractiveindexslightlylessthan1)andreflected(atverysmallangles)WhenX-rayshitaspecimen,theinteractioncanresultinvarioussignals/emissions/effects.Thecoherent

6、lyscatteredX-raysaretheonesimportantfromaXRDperspective.Incoherent(Comptonmodified)FromlooselyboundchargesClickheretoknowmoreNowweshallconsidertheimportanttopicastohowX-raysinteractwithacrystallinearray(ofatoms,ionsetc.)togiverisetothephenomenonknownasX-raydiffraction(XRD).Letusconsideraspecia

7、lcaseofdiffraction→acasewhereweget‘sharp[1]diffractionpeaks’.Diffraction(withsharppeaks)(withXRDbeingaspecificcase)requiresthreeimportantconditionstobesatisfied:RadiationrelatedCoherent,monochromatic,parallelwaves&(withwavelength).Sam