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1、材料工程基础FoundationofMaterialsandEngineering华北水利水电大学杨中正CrystalstructureMaterialsinaction—crystalstructureManymaterialscrystallizeinaregulararraywithbasicbuildingblocksbeingrepeatedatregularintervals.Theiractualstructureisdeterminedbythebondcharacterandrequirmentthattheenergyofthesyste
2、mbeminimized.Cryatalmaybeformedinmetals,ceramics,andevenpolymers.Symmetry,atoms,andbondsetc.Crystalstructure3.1引言Macroscopicpropertiesofmaterialsareinfluencedstronglybyatomicscalestructure.Inpreviouschapterswefocusedourattentiononanindividualatomorion,spatialrelationshiptoasmallgro
3、upofatomsknownasitsnearestneighbours,asmanifestedinitscoordinationnumberandbonds.Localarrangementofnearest-neighouratomsaboutacentralatomisknownasshort-rangeorder(SRO)短程有序（short-rangeorder,SRO）：在一个原子周围最临近原子的局部呈现有序的排列。长程有序（LRO)：在比键长大得多的距离呈现有序的排列。Orderoverdictancemuchgreaterthanthebo
4、ndlength.AmorphoussolidshowSROinthreedimensions,butnoLRO.Amorphoussolid,orglassesissimilartothatofa“frozen”liquid.CrystallinesolidexhibitbothSROandLROinthreedimensions.Asageneralrule,mostmetalsarecrystaline,whileceramicsandpolymersmaybeeithercryatlline,amorphousoracombinationofthet
5、wo.Inthechapter,wedescribefirstlythattheconceptofacrystallattice,andthengiveafewsimplecrystalstructures.Next,wedescribethefundamentalrelationshipbetweencrystalstructureandmacroscopicpropertiers.3.2布拉维点阵和单胞BravaislatticesandtheunitcellsLatticecanbedefinedasanindefinitedlyextendedarr
6、angementofpointseachofwhichissurroundbyanidenticalgroupingofneighboringponts.点阵可以定义为无限延伸的排列，其中每一个点都被相同类型的临点所包围。SevenCrystalSystemsTriclinic(三斜）a≠b≠c，α≠β≠γ≠90°Monoclinic（单斜）a≠b≠c，α＝β＝90°≠γα＝γ＝90°≠βOrthorhombic（正交）a≠b≠c，α＝β＝γ＝90°Tetragonal（四方）a＝b≠c，α＝β＝γ＝90°Cubic（立方）a＝b＝c，α＝β＝γ＝90°He
7、xagonal（六方）a＝b≠c，α＝β＝90°γ＝120°Rhombohedral（菱形）a＝b＝c，α＝β＝γ≠90°Latticepoints:theverticesoftheunitcell.Latticeparameters:thelengthsoftheunit-celledges.Theanglesandlengthswithintherepeatunitdeterminetheclasstowhichthelatticecellbelongs.Howtodistinguishthesizeandshapeofthedeferentunitce
8、ll?Thesixvariables,whichar
