材料化学全英文课件第10课

材料科学基础

Fundamental

ofMaterialsScienceProf:TianMinBo

Tel:62795426，62772851 E-mail:tmb@DepartmentofMaterialScienceandEngineeringTsinghuaUniversity.Beijing100084

Lessonten3.7IntermetallicCompounds

(IntermetallicPhases)3.7.1Feature1.ThestructureofAmBndiffersfromthoseofeitherAorB2.Itscompositionisvariabletomoreorlessextension3.Mixedbonding4.Intermediateproperties3.7.2Formation

A→←BThepropertyofAmBnisbetweenthatofAandB.3.7.3Factorgoverningthestructureof“compounds”.1)Electrochemicalfactor(X)2)Electronconcentration(e/a)3)SizefactorMetal,Nonmetal,Metalloid3.8NormalValenceCompounds3.8.1Definition:

Ifthenumberofvalenceelectronsofthecationissufficienttocompleteoctahedronoftheanion,thecompoundiscalledthenormalvalencecompounds.Example:CmAn

meC＝n(8－eA)sometimes:m(eC－eCC)＝n(8－eA－eAA)3.8.2Classification

accordingtostructure1.NaClandCaF2types

NaCltype:(MgCaSrBa)(SeTe)(MnPbSn)(SeTe)CaF2type:PtSn2PtIn2Pt2PAnti-CaF2type:Mg2(SiGeSnPb)Cu2SeLi3AlN2LiMg(NAsSbBi)AgMgAs

2.Diamond,Zincblende,WurtzitetypesZincblende:(BeZnCaHg)(SSeTe)(AlGaIn)(PAsSb)Wurtzite:(ZnCdMn)S(CdMn)Se3.NiAsstructureExample:

(CrFeCoNi)(SSeSb)(FeCo)Te(MnFeNiPtCn)SnNi(AsSbBi)StructureNormalstate——Ni:As=1:1As:HCPNi:octahedralinterstitialsiteWhenNidoesnotfullfilloctahedralinterstitialsite

Ni:“As”<1:1,forNiTe2(1:2)Extremestate：Nioccupytrigonalinterstitialsite

Ni:“As”>1:1,forNi2In(2:1)Ni2In—NiAs—NiTe2c/anormalvalencetransitionioniccompoundⅢB:needs5electronsⅥB:needs2electrons3.9ElectronPhases

(Hume-RotheryPhases)3.9.1DefinitionForAlloysofIBortransitionmetals,andBgroupmetalsphaseswithsaneorsimilarstructureoccuratapproximatelysomeelectronconcentration(e/a)thesealloysarethereforecalledaselectroncompounds.3.9.2Feature:⑴Identicalonsimilarstructureoccursatapproximatelythesameelectronconcentration,e/a.

⑵ComponentsIBortransitionmetal＋metalsinBgroup⑶Compositionrangeisrelatedtoe/a⑷Metalliccharacter3.9.3Valenceelectronconcentration:(e/a)Valenceoftransition-metal:0ValenceofB-metalequalstoitssubgroupnumberForexample:

CuZn:β

e/a=(1+2)/2=21/14≈1.36Cu5Zn8:γ

e/a=(5+16)/(5+8)=21/13≈1.48CuZn3:ε(HCP)e/a=(1+6)/(1+3)=7/4≈1.743.10SizeFactorCompounds3.10.1Interstitialphases(Interstitialcompounds)

ConditionA

>>B

TheatomicsizeofB:H(0.46),B(0.97),C(0.77),N(0.71)Å1.SimpleinterstitialcompoundstructureA:TransitionmetalsB:Interstitialelements(H,B,C,N)2.Complexstructure

M3C(Fe3C),M23C6,M6CPropertiesofinterstitialcompounds⑴somemetallicproperties⑵hardandbrittle⑶thecompositionisvariabletomoreorlessextension⑷forsizefactorcompoundsthestructuremainlydependson.1.Threeprinciplesforthestructure

①Space-fillingprinciple:Atomstendtofillthespaceascloselyaspossible

②Symmetryprinciple:Atomstendtobuildaconfigurationofhighsymmetry

③Principleofmulti-dimensionalconnection3.10.2Topologicallyclosepackedphases2.Lavesphases

MgCu2MgZn2MgNi2①ThezcoordinatesofMgatomics:0,,,,1

Theface-centredatomsarenottangenteachother.②ThezcoordinatesofCuatoms:

③④TheCNforCuandMgatomsinMgCu2A

atomsB

atoms⑤3.phaseACrMoWVBMnFeCoNiDiscussionManyfactorsS.S.vscompoundNitrideSuperhardmaterialsExercise1.Summarizeandcomparenormalvalencecompounds,electroncompounds,TCPphasesandinterst