第2课-晶体结构2教学课件.ppt

二、晶体结构-2(CrystalStructure)*(Spacegroup)14个布拉菲格子(Bravaisspace)32个点群(pointgroups)230个空间群(spacegroups)对称元素:(Symmetryelements)旋转轴(1,2,3,4,6)(Rotationaxis)镜面m(Mirrorplane)对称中心i(Inversioncenter)四次倒转轴(Rotoinversionaxis)滑移面g(Glideplane)平面,滑移线(Glideline)平面,镜线(Mirrorline)螺旋轴np(Screwaxis)*Theglidetranslationvector,t,,用a,b,c各表示,沿a,b,c方向平移对应轴一半后又反映;,用n表示,平移(a+b)/2,(b+c)/2,(a+c)/2,(a+b+c)/2,再反映;,用d表示,滑移量为(a+b)/4,(b+c)/4,(a+c)/4,(a+b+c)/4,再反映;滑移(Glidetranslation)*螺旋(Rototranslation) 对称元素:螺旋轴(Screwaxis)Ascrewaxisofordernoperatesonanobject:(a)arotationof2π/ncounterclockwise(b)atranslationbyavectortparalleltotheaxis,inapositivedirection31(pronouncedthreesubone’)**Thespacegroupsymbolconsistsoftwoparts:(i),acapitalletter,indicatingthelatticethatunderliesthestructure;(ii),,forprimitive,notH,whichmeansacentredhexagonallattice.*Thesecondpartofaspacegroupsymbolconsistsofone,,which,whenapplied,allowalloftheothersymmetryoperationstoberecovered.*,thetwosymbolsaredivedbyaslash,asinthespacegroupP2/m(pronounced‘Ptwooverm’).*,theinitiallatticeletterofthespacegroupisignored,andthetranslationsymmetryoperators,a,b,c,n,d,arereplacedbythemirroroperator,m.*空间群的图示:(Thegraphicalrepresentationofthespacegroups)