材料科学基础(清华大学)

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1、材料科学基础FundamentalofMaterialsProf:TianMinBoTel:62795426，62772851E-mail:tmb@mail.tsinghua.edu.cnDepartmentofMaterialScienceandEngineeringTsinghuaUniversity.Beijing100084§2.1SpaceLatticeⅠ.Crystalsversusnon-crystals1.ClassificationoffunctionalmaterialsChapterⅡFundamenta

2、lsofCrystallographyLessonthree2.ClassificationofmaterialsbasedonstructureRegularityinatomarrangement——periodicornot(amorphous)Crystalline:Thematerialsatomsarearrangedinaperiodicfashion.Amorphous:Thematerial’satomsdonothavealong-rangeorder(0.1～1nm).Singlecrystal:inth

3、eformofonecrystalgrainsPolycrystalline:grainboundariesⅡ.Spacelattice1.Definition:Spacelatticeconsistsofanarrayofregularlyarrangedgeometricalpoints,calledlatticepoints.The(periodic)arrangementofthesepointsdescribestheregularityofthearrangementofatomsincrystals.2.Twob

4、asicfeaturesoflatticepointsPeriodicity:Arrangedinaperiodicpattern.Identity:Thesurroundingsofeachpointinthelatticeareidentical.Alatticemaybeone,two,orthreedimensionaltwodimensionsSpacelatticeisapointarraywhichrepresentstheregularityofatomarrangements(1)(2)(3)abThreed

5、imensionsEachlatticepointhasidenticalsurroundingenvironmentⅢ.UnitcellandlatticeconstantsUnitcellisthesmallestunitofthelattice.Thewholelatticecanbeobtainedbyinfinitiverepetitionoftheunitcellalongit’sthreeedges.Thespacelatticeischaracterizedbythesizeandshapeoftheunitc

6、ell.Howtodistinguishthesizeandshapeofthedeferentunitcell?Thesixvariables,whicharedescribedbylatticeconstants——a,b,c;α,β,γLatticeConstantsacbαβγacbαβγ§2.2CrystalSystem&LatticeTypesIfarotationaroundanaxispassingthroughthecrystalbyanangleof360o/ncanbringthecrystalintoc

7、oincidencewithitself,thecrystalissaidtohavean-foldrotationsymmetry.Andaxisissaidtoben-foldrotationaxis.Weidentify14typesofunitcells,orBravaislattices,groupedinsevencrystalsystems.Ⅰ.SevencrystalsystemsAllpossiblestructurereducetoasmallnumberofbasicunitcellgeometries.

8、Thereareonlyseven,uniqueunitcellshapesthatcanbestackedtogethertofillthree-dimensional.Wemustconsiderhowatomscanbestackedtogetherwithinagiv