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陈小龙
中国科学院物理研究所

2006.10杭州IsostructuralCompoundsXRDpatternsofSolidsolutionNaSr4-xBaxB3O9(0≤x≤4):FirstcubicborateonlywithBO3PhasetransitionofBaTiO3fromtetragonaltocubicatabout132˚CYBa3B3O9:PhasetransitionandstructuredeterminationLiAlB2O5:SearchfornewSHGmaterialsStructuralDataforLiAlB2O5FinalRefinementofNewcompoundofLiAlB2O5StructurevsTemperature:KCaCO3FLiSr4B3O9:Acomparisonbetweenstructuredeterminationfromsingle-crystalandpowderX-raydiffractionWhatisaRietveldRefinement?WhatcanwegettoperformaRietveldrefinement?HistoryReviewAminoffPrize,Stockholm,1995StructuralmodelHowRMworks?Givenasolution=opt(1,2…p)thatapproximatelysatisfytheaboveequation.Tofindabettersolution,webeginaniterativeprocessbyexpandingintoaTaylorseries.A1=bSisthescalefactorofthephaseLhcontainstheLorentz,polarisationandmultiplicityfactors.FhisthestructurefactorAhistheabsorptioncorrectionPhisthepreferredorientationfunctionΩisthereflectionprofilefunctionthatmodelsbothinstrumentalandsampleeffectswhere,fiatomicscatteringfactorforithatom
xi,yiandzithefractionalcoordinatesforithatomWhereRELAXisrelaxtionfactorsthatareusedtocontroltheshiftstoavoiddivergence;
andCCisamultiplier.WhatweneedtoperformaRR?

Asetofstep-modescanneddata,
usually2=10-120˚ormore,step2˚
collectingtimeisinstrumentdependentfrom1-20s
forlaboratorydiffractometer;

Aninitialstructuralmodelhavingroughlyaccuratelattice
constants,correctspacegroupandapproximateatomicpositions
Howweobtainaninitialstructuralmodel?

-solidsolutionsusuallyadoptsamestructuretypesoftheirparentcompounds;
NaSr4-xBaxB3O9(0≤x≤4)

Compoundswithsamechemicalformula
YBa2Cu3O7andNdBa2Cu3O7
butalwaysalertthatexceptionsarenotuncommon
La2CuO4andNd2CuO4

Tryanderror

Abinitostructuredetermination
Isthecompoundknown?CrystallographicStructureDatabasesAnewstructuraldatabase(2003):
aimedatfreelyretrievingdataParametersinPCRfileCodewords(I)Codeword(II)Codeword(III)Codeword(IV)Codeword(V)ModelingbackgroundsControlflagsWhereBmareparametertoberefined
BKPOSisauser-specifiedparameter,o