材料科学基础(清华大学)

《材料科学基础(清华大学)》由会员上传分享，免费在线阅读，更多相关内容在教育资源-天天文库。

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

2、ntalsofCrystallographyLessonthree2.ClassificationofmaterialsbasedonstructureRegularityinatomarrangement——periodicornot(amorphous)Crystalline:Thematerialsatomsarearrangedinaperiodicfashion.Amorphous:Thematerial’satomsdonothavealong-rangeorder(0.1～1nm).Singlecrysta

3、l:intheformofonecrystalgrainsPolycrystalline:grainboundariesⅡ.Spacelattice1.Definition:Spacelatticeconsistsofanarrayofregularlyarrangedgeometricalpoints,calledlatticepoints.The(periodic)arrangementofthesepointsdescribestheregularityofthearrangementofatomsincrysta

4、ls.2.TwobasicfeaturesoflatticepointsPeriodicity:Arrangedinaperiodicpattern.Identity:Thesurroundingsofeachpointinthelatticeareidentical.Alatticemaybeone,two,orthreedimensionaltwodimensionsSpacelatticeisapointarraywhichrepresentstheregularityofatomarrangements(1)(2

5、)(3)abThreedimensionsEachlatticepointhasidenticalsurroundingenvironmentⅢ.UnitcellandlatticeconstantsUnitcellisthesmallestunitofthelattice.Thewholelatticecanbeobtainedbyinfinitiverepetitionoftheunitcellalongit’sthreeedges.Thespacelatticeischaracterizedbythesizeand

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

7、ingthecrystalintocoincidencewithitself,thecrystalissaidtohavean-foldrotationsymmetry.Andaxisissaidtoben-foldrotationaxis.Weidentify14typesofunitcells,orBravaislattices,groupedinsevencrystalsystems.Ⅰ.SevencrystalsystemsAllpossiblestructurereducetoasmallnumberofbas

8、icunitcellgeometries.Thereareonlyseven,uniqueunitcellshapesthatcanbestackedtogethertofillthree-dimensional.Wemustconsiderhowatomscanbestackedtogetherwithinagiv