含不同成分尿素的夾層化合物nh2conh2xi2的制備及其熱、電輸運性質(zhì)

含不同成分尿素的夾層化合物nh2conh2xi2的制備及其熱、電輸運性質(zhì)

1非價值主義定義tis2hasananisodic結(jié)構(gòu)與a3個a.m.3m.它是一個知道的兩個直接組織（1t，2h），以及作為一個緩慢排列的有序布局。當(dāng)?shù)豤oordinal證據(jù)：第一tis2和第二tis2是地方coordinal證據(jù)（2h）。tis2的主要受害者是tis2（1噸，2噸，2噸），tis6c2可作為一個整體配置，而tis2是兩個行的接受者。鋼條的跡象是，通過緩慢排列的有序排列，以及緩慢排列的特征。緩慢排列的鐵線蓮是一個整體。Layered-structuredTiS2iswellknownforitscapabilityofintercalationbyawiderangeofelementsintoitsvanderWaalsgap.SinceLi+caneasilyintercalateandleavevanderWaalsgapofTiS2,ithasbeenstudiedasapromisingcathodematerialforrechargeablelithium-ionbatteries.BesidesLi,transitionmetals,suchasFe,CoandNi,havebeensuccessfullyinsertedintothegapofTiS2,andinfluencesofthisintercalationonthephysicalpropertiesofthecorrespondingcompoundswereinvestigatedandexplored.Specially,H.ImaietalreportedthatTiS2haslargethermopowerSandpowerfactor(S2/ρ,ρiselectricalresistivity)atroomtemperature,indicatingthatTiS2isapotentialcandidateforthermoelectricapplications.Veryrecently,theworkinourgroupindicatedthatlargeenhancementofthermoelectricpropertiesforTiS2canberealizedbyproperBiinteractionintoitsvenderWaalsgap.Astoreductionofthermalconductivity,Slackproposedthatacrystalstructurecontainingweaklyboundatomsormoleculesthat“rattle”withinatomiccagescouldreducelatticethermalconductivity,andlatterexperimentsprovedhisidea.AccordingtoSlack’stheory,ourgrouphavecompletedsomeworks:intercalationofheavyelementBi,Gd,NdintoTiS2mayreduceitsthermalconductivitybyatomic“rattling”andraiseitsthermoelectricproperties,anddopingatTisitewithmetalelementsNi,Mg,Cdcanalsoadjustitsproperties.Nevertheless,toourknowledgelittleworkaimedatimprovingthermoelectricpropertiesofTiS2bymeansofintercalationoforganiccompoundshasbeenreported.NH2CONH2intercalationintoTiS2wouldhaveprofoundinfluenceontheoverallphysicalpropertiesofitsintercalatedcompounds,whichonehardlyknownindetail.Inourwork,intercalatedcompounds(NH2CONH2)xTiS2havebeensynthesizedbymoistchemicalmethodinautoclave,anditsthermalandelectricalpropertiesareinvestigated,andtheresultsindicatethatNH2CONH2intercalationintoTiS2candecreaseitsthermalconductivityeffectively.2u2004范圍Polycrystalsofureaintercalatedcompounds(NH2CONH2)xTiS2werepreparedbythree-stepprocedure.Firstly,TiS2powderwaspreparedbydirectreactions(inanevacuatedquartzampoule)oftitaniummetalpowder(99.99%)tosulfurpowder(99.999%)at610℃for7days.Secondly,ureawasdissolvedinorganicimpregnantbenzenegainedthesolutionwithacertainconcentrationC(≈12.5,25,50mmol/L,respectively),andwedefinedthenamesforthesampleswithdifferentintercalationcontents,S1#,S2#,S3#forureaintercalatedcompoundssynthesizedbydifferentconcentrationsC≈12.5,25,50mmol/L,respectively.Thirdly,TiS2andthebenzenesolutionofureawereloadedintotheautoclave,whichwereheat-treatedat393Kfor15hours,thenleachedtheintercalatedcompoundfromthesolution.Thebulkspecimensfortransportpropertymeasurementswereobtainedbypressingat300MPa,350Kinvacuum.ThephasestructuresandthecompositionsoftheobtainedsampleswerecheckedbyusingX-raydiffraction(XRD,CuKαirradiation)andEnergyDispersiveX-raySpectroscopy(EDS),respectively.Accuratemeasurementsoflatticeparameterswererealizedthroughcalibrationwithsiliconstandard.Latticestrainswereestimatedfromlinebroadeningofthereflectionpeakswhereinstrumentalbroadeningwascalibratedusingasiliconstandard.Theinfrared(IR)spectrawereobtainedbyFourierTransformInfrared(FTIR)(Ramanspectrometer(NicoletCorp.USA)atroomtemperature.Tomeasuretheirthermoelectricproperties,thesynthesizedpowderswerecompactedbypressing(underthepressureof300MPa)invacuumatroomtemperaturetoobtainbulksampleswiththesizeof30mm×10mm×(～)1.5mm.Thenbar-shapedspecimensofthesize13mm×3mm×(～)1.5mmwerecutfromthebulksamplesforthemeasurements.Fourprobes(Custraps)wereelectricallyandthermallyattachedtothespecimensbysilverconductiveadhesivepaste(PhentexCorp.USA)tomeasuretheirDCresistance,andwhenthermopowerandthermalconductivityweremeasuredthemiddletwoprobeswereusedtoexploretemperaturegradient(difference)andpotentialdifference.Allthethermoelectricproperties(DCresistance,thermopowerandthermalconductivity)weremeasuredsimultaneouslybyusingaphysicalpropertymeasurementsystem(PPMS,QuantumDesign,USA)inthetemperaturerangefrom5to310K.3.影響因素的決定3.1pe直利克氏體laticinpincipackuregas3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.Figure1showsXRDpatternsforthesynthesizedspecimensS1#,S2#andS3#.ItcanbeseenfromFig.1thatallthemainpeaksontheXRDpatternsmatchwellwiththoseforstandardTiS2(JCPDS:65-3369),indicatingthattheintercalatedspecimenshavethesamecrystallographicstructureasthatofTiS2.However,astheureaintercalatedintothevanderWaalsgapsofTiS2,someureaformingadmixturewithTiS2,sotherehavefewpeaksofureaoccurredintheXRDpatterns,forexample,thepeakaround2θ=22.5degreeisthe(110)peakofurea,andtheintensityofthispeakenhanceswiththeincreasingofureaaddition,implyingthatsomeureamaybeformadmixturewithTiS2insteadofintercalatingintothevanderWaalsgapsofTiS2.Latticeparametermeasurement(Fig.2)indicatedthatlatticeconstantcexpandedfrom5.6953nmto5.7056nmfromstandardTiS2toS3#,correspondingly,latticeachangedslightlyfrom3.4073to3.4047nm.ThedecreaseoflatticeconstantacouldbeexplainedthattheshrinkofthelatticesduetotheCoulombattractionbetweentheH+ofamidogen(-NH2)inureaandtheS2-oftitaniumdisulfide.TheseresultsindicatedthatureamoleculeweresuccessfullyintercalatedintothevanderWaalsgapsofTiS2,formingintercalationcompounds(NH2CONH2)xTiS2,whichcausedlatticeconstantcincreasingwiththeintercalationofureamolecule,andlatticeconstantadecreasingthatisobviouslydifferentfromtheintercalationofmetalatoms.Tocharacterizetheureaintheintercalatedcompounds(NH2CONH2)xTiS2,wehaveobtainedtheIRspectra(Figure3)byFTIRspectrometer.Fig3showthattheIRspectraofthespecimensS1#,S2#,S3#.Itcanbefoundthat8peaks(around3798,3429,2929,2388,2300,1630,1053,669cm-1)appearedintheIRspectrumsoftheureaintercalatedcompounds.Itisknownthatthepresenceofabsorptionpeaksat1630cm-1,canbeassignedtovibrationalfrequenciesofC=Obandvibration,whilethebroadpeakabsorptionat3429cm-1isassignedtotheN-Hbandvibration,whicharethatthecharacteristicpeaksofurea.3.2tis2sivitivitizactsit3.TheDCelectricalresistivityversustemperaturefortheureaintercalatedspecimensS1#,S2#,S3#inthetemperaturerangeof5～310KispresentedinFig.4.Inotherreports,pureTiS2showsametal-likebehavior(i.e.,dρ/dT>0).However,theρ～Tcurvesoftheintercalatedcompounds(S1#,S2#,S3#)showasemiconductor-likebehavior(i.e.,dρ/dT<0)inwholetemperaturerangeinvestigated.ThisisquitecontrarytothatformetalintercalatedcompoundsMxTiS2,whosemetallicbehaviorenhancesafterintercalationofguestelements,indicatingthatthemechanismofelectrontransferafterorganiccompoundureaintercalateintotheVanderWaalsgapsofTiS2isdifferentfromthatofmetal(Bi,Li)intercalation.Inotherwords,presentresultindicatesthatatransitionfrommetal-liketosemiconductor-likebehavioroccursafterureaintercalatingintotheVanderWaalsgapsofTiS2.Inaddition,theelectricalresistivityofureaintercalatedcompounds(NH2CONH2)xTiS2increasesmonotonouslywithincreasingureaconcentrationintheimpregnantatthewholetemperaturerange,whichisalsocontrarytothephenomenaobservedinmetalintercalatedTiS2whereitsresistivityalwaysdecreasedwithincreasingthecontentofintercalatedelements,ashasbeenobservedinBixTiS2andLixTiS2.Thereasonwhy(NH2CONH2)xTiS2transitsfrommetallicbehavior(x=0)tosemiconductingbehavior(x>0:S1#,S2#,S3#)afterintercalatingwithureamaylieinthefactthatTiS2isasemiconductorwithnarrowband-gap.However,inpractice,self-intercalationofTiintoTiS2isunavoidableinthesynthesisprocess.Asaresult,TiS2appearsalmostalwaysasextrinsicsemiconductor.Moreover,ifionizationenergyofself-intercalationTiatomsissmallenough,completeionizationwilloccuratthelowtemperaturesthatcanbereachednormally.IfthenumberofintercalatedTiatoms(actingasdonors)issufficientlarge,adegeneratesemiconductorwillformwhichbehavesmetallically,asjustobservednormallyinTiS2.Asintercalationofureaoccurredintheintercalatedcompounds,accepters(theH+ofamidogen(-NH2)inurea)willbeintroduced.Thenthecarrier(electron)concentrationwilldecreaseifcompensationeffecttakesplace.Consequently,asureacontent(numberofaccepters)ishighenough,de-degenerationofTiS2willoccur,leadingtoappearanceofthesemiconductorbehavior.Inotherwords,theintercalationoforganiccompoundureawouldrevealthenatureofTiS2asanarrowsemiconductor,whichwascoveredbyitsmetallicbehaviorresultingfromhighdegreeofdegeneration.BybestfittingtheexperimentaldatatoMott’svariablerangehopping(VRH)law,wefindthattheconductivitydataof(NH2CONH2)xTiS2(x>0:S1#,S2#,S3#)incorrespondinglow-temperaturerangesareingoodagreementwithMott’stwo-dimensional(2D)VRHmodel,i.e.:σ=σ0exp[?(T0T)1/3](1)σ=σ0exp[-(Τ0Τ)1/3](1)whereT0=8/((kN(EF)lv2)isthehoppingbarrier,and(0isaconstant.Figure5showstheplotsoflnσversusT-1/3fortheintercalatedspecimens.ItcanbeseenthattherearegoodlinearrelationsbetweenlnσandT-1/3atlowtemperaturesforS1#,S2#andS3#,suggestingthatTiS2has2Dtransportcharacteristics.ThefittedvaluesofT0are40.4K,46.7Kand76.9KforS1#,S2#andS3#,respectively.Generally,thevariationoflocalizationlengthlvisnotverystrong.Therefore,theincreaseofT0withincreasingureacontentx(<0.15)wouldlargelyreflectdecreaseinstatedensity(N(EF))atFermisurfacewithcarrierconcentration.Itisunderstandablethatasureacontentincrease(fromS1#toS3#)Fermilevel(EF)decreasewithdecreasingthecarrier(electron)concentrationduetocompensationeffect.3.3u2004范圍lattingThetemperaturedependencesoftotalthermalconductivityκforintercalatedcompounds(S1#,S2#,S3#)areshowninFig.6.Itcanbeseenthatintercalatingofureacausedecreaseintheirthermalconductivity.SimilartothatofpureTiS2(thethermalconductivitydataofpureTiS2werecitedfromreference),thethermalconductivityκoftheintercalatedcompoundsshowsweakdependenceabove～70K,belowwhichκofallthecompoundsincreasesrapidlyandapproximatelylinearlywithincreasingtemperature.OnenoticesfromFig.6thatthelatticethermalconductivityofureaintercalatedcompounds(S1#,S2#,S3#)isobviouslysmallerthanthatofpureTiS2,specially,thethermalconductivityκofS1#about1.5Wm-1K-1atroomtemperature,onlyishalfvalueofpureTiS2.Thisdeceaseoflatticethermalconductivitymayoriginatefromintercalationoftheorganiccompoundureamolecules,whichhavebiggervolumeofcell(150.63?3)andcouldcausephononscatteringbylow-frequencyvibrations,or“rattling”,oftheintercalatedureamoleculesinthevanderWaalsgapofTiS2,ashasbeenshowninBixTiS2.Bycomparison,“rattling”oftheintercalatedureamoleculesinthevanderWaalsgapsofTiS2wouldbeeffectiveinreducingitslatticethermalconductivity,andtheresultscanfurtherconfirmureamoleculesintercalatedtothevanderWaalsgapsofTiS2successfully.ThevariationsoftheSeebeckcoefficient(S)for(NH2CONH2)xTiS2withtemperatureareshowninFig.7.ThenegativevaluesoftheSeebeckcoefficientobservedforallofthespecimensovertheentiretemperaturerangeshowthatthemajorchargecarriersin(NH2CONH2)xTiS2areelectrons,asmention