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1、衍射花样指数化Thefirststepinanalysingunknownpowderpatternisoftenanattempttofindaunitcellthatexplainsallobservedlinesinthespectrum.Youdonotneedadditionalcrystallographicdata,althoughifitexistsitmakesforfasterandmorereliableresults.Thematerialtobeanalysedmustbesinglephasedandtheexperimentalma
2、terialmustbeveryaccurate.Indexingprogramsuseonlythepositionalinformationofthepatternandtrytofindasetoflatticeconstants(a,b,c,a,b,g)andindividualMillerindices(hkl)foreachline.Theformofequationstosolveiscomplicatedforthegeneralcase(triclinic)indirectspacebutisstraightforwardinreciproca
3、lspace.Inthelatterthesetofequationsis：Q=h2A+k2B+l2C+hkD+hlE+klFwheretheQ-valuesareeasilyderivedfromthediffractionangleQ.Thissethastobesolvedfortheunknowns,A,B,C,D,E,F,whichareinasimplewayrelatedtothelatticeconstants.Findingthepropervaluesforthelatticeparameterssothateveryobservedd-sp
4、acingsatifiesaparticularcombinationofMillerindicesisthegoalofindexing.Itisnoteasyevenforthecubicsystem,butitisverydifficultforthetriclinicsystem.Therearetwogeneralapproachestoindexing,theexhaustiveandtheanalyticalapproach.Bothoftheseapproachesrequireveryaccurated-spacingdata.Thesmall
5、ertheerrors,theeasieritistotestsolutionsbecausethereareoftenmissingdatapointsduetointensityextinctionsrelatedtothesymmetryorthestructuralarrangementorduetolackofresolutionofthed-spacingthemselves.Theearliestapproacheswereoftheexhaustivetypeandweredonebygraphicalfittingornumericaltabl
6、efitting.IndexingProgramsThemethodscurrentlyimplementedareshownbold.TheyareselectedthroughtheitemIndexinginthemainmenu.ProgramAuthorTypeITOVisseranalyticalTREORWernerexhaustivePOWDERDICVOLCUBICTheprogramsuseasetofcommonparameters,e.g.thewavelengthandamethodspecificset.Afteryouhavecli
7、ckedonaprogramwiththeleftmousebuttonindexingisimmediatelystartedwiththeactiveparameterset.Dependingontheproblemandcomputertypetheprogramruncantakefromsecondstomanyminutes.Allsolutionsarecomputedandstoredinternally.The"best"oneisdisplayedatthetopofthescreen,thenexttobestatthebottom.Fo
8、ranoverviewo
