简介:采用自蔓延高温合成技术(SHS)制备固体氧化物燃料电池(SOFC)阴极材料La1-xSrxMnO3(LSM);研究成形压力、稀释剂添加量等参数对反应过程及合成产物性能的影响;采用XRD、ICP研究SHS法合成LSM的物相和晶型结构.结果表明:自蔓延高温合成产物为钙钛矿结构菱方晶系La1-xSrxMnO3,Sr含量的变化引起合成产物特征峰的位置和半峰宽变化;随着Sr含量的增加,合成的LSM粉末粒度变细,晶格常数a和c减小.
简介:Duetotheremarkablemagnetoresistance(MR)effectonperovskite-typemanganite,magnetoelectronicsandspintronicshavebecomeattractivesubjectsofexperimentalandtheoreticalinvestigationsfortheapplicationpurpose.(La0.9Nd0.1)2/3Ca1/3Mn1-xFexO3(x=0,x=0.05)werepreparedsuccessfullybysol-gelmethod.Thestructure,magneticproperties,andtransportpropertiesofthecompoundswereinvestigated.Themagnetoresistanceeffectdependsonthecompositionandthetemperature.XRDpatternsshowthatthecompoundisasinglephasepolycrystalwithpseudocubicstructure.Alargenegativeisotropicmagnetoresistanceeffectinthesampleswereobservedatlowtemperatureregion.ThemaximumMRofthesampleswas77%and97%,respectively.Itwasmostlikelyduetothescatteringorthetunnelingtransportofspin-polarizedcarriersinlatticeunderstrongmagneticfield.
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简介:ThemeasurementsoftemperaturedependenceofthemagneticsusceptibilityofLa1-xSrxCoO3perovskiteoxidesatdifferentSrdoping(0≤x≤0.5)andannealingtemperaturewerepresented.Forthesamplewithx=0.1,ashoulderwasobservedaround150K,andapeakwhichisonefeatureofspinglassappearedaround50Kinthecurveofsusceptibilityversustemperature.Thehigh-temperature(250~420K)susceptibilityfitswellwithCurie-Weisslawforallsamples.WeissconstantandeffectivemagneticmomentweredeterminedandtheirvariationswithSrdopingandoxygenannealingconditionwereobtained.TheWeissconstantincreasesmonotonouslywithSrcontentforx>0.2.Thevaluesofeffectivemomentswereinterpretedwiththespinstateofcobaltions.Studiesonthesusceptibilitiesofthesampleswithx=0.2underdifferentpreparationtemperaturesandannealingtemperaturesshowthattherisingofsinteringtemperatureandannealingtemperaturewillincreasethepara-ferromagnetictransitiontemperature,andreducetheeffectivemomenttonormalvalue.OurresultshowsthatbothCo3+andCo4+ionsshouldbeinISstateafterannealingandtheoxygenannealingcausesthetransitionofCo3+spinstatefromHStoIS.
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简介:TheLa3+-loadedadsorbentwaspreparedbythereactionbetweenLa3+andethanolamine-modifiedvegetabletannicextract,totreatF--containingwastewater.TheproblemsofheavycolorcausedbyvegetabletannicextractandofturbiditycausedbyreactionbetweenLa3+andF-weresolved.Whenotherconditionswerenotchanged,pH,temperature,stirringtime,anddosewerechangedrespectivelyandtheadsorbancewastestedrespectively.Theresultsshowthatthisadsorbentpossesseshighsaturatedadsorptivecapacity(18.86mg·g-1)whenpHis5~6,T≤80℃,0.2gdosage,and180minagitatingtime,andtheadsorbancereachesthehighest(98.5%).Theadsorbentcanbeeasilyregeneratedwith0.5mol·L-1NaOHatpH12.
简介:AseriesofLa2O3/MCnylonnanocompositeswerepreparedviainsitupolymerization.Theeffectsofcontentofnano-La2O3onthemechanicalpropertiesofnanocompositeswerestudied.Dispersionofnano-La2O3inMCnylonmatrixwasobservedwithSEM.ThecrystalstructureofnanocompositeswascharacterizedbymeansofXRD.SEManalysisshowsthatLa2O3nanoparticlesareuniformlydispersedinMCnylonmatrixandlittleclusteringexistswhenthecontentofnano-La2O3islowerthan1%,however,whenthecontentofnano-La2O3ismorethan1%,itbeginstocluster.XRDanalysisindicatsthatnano-La2O3doesnotchangethecrystalstructureofMCnylon.Mechanicalpropertiestestsshowthatthetensilestrength,elongationatbreak,impactstrength,flexuralstrength,andflexuralmodulusofnanocompositesfirstincreasethendecreaseasthecontentofnano-La2O3isincreased.Whenthecontentofnano-La2O3is0.5%,thetensilestrengthandelongationatbreakofnanocompositesreachmaximum,whichare17.9%and52.1%higherrespectivelythanthoseofMCnylon.Whenthecontentofnano-La2O3is1.0%,theimpactstrength,flexuralstrengthandflexuralmodulusofnanocompositesreachmaximum,whichare36.6%,12.7%and16.3%higherrespectivelythanthoseofMCnylon.
简介:Inthispaper,varioustechniquesincludingBET,XRD,SEMandXPSwereusedtostudythesinteringofpureandLa2O3-dopedtitania.Theexperimentalresultsshowthatsinteringoftitaniaproceedsviavolumediffu-sion.Addingoflanthanumoxidedecreasestherateofsinteringandhindersthephasetransitionfromanatasetorutilecrystalbystrongsurfaceinteractionbetweenthemixedcrystals(La4Ti9O24,La0.66TiO2.99)andTiO2.
简介:15%Ag-addedcubicperovskitesSr0.9La0.1TiO3andRuddlesden-Popper(RP)phasesSr2.7La0.3Ti2O7werefabricatedviahydrothermalsynthesis,coldpressingandhigh-temperaturesintering.Thestructureandthermoelectricpropertieswerealsoinvestigatedforallsamples.TheresultsindicatedthatAgprecipitatedasasecondphase.AgadditionmadeelectricalconductivityandabsoluteSeebeckcoefficientenhanced,asaresult,theZTvalueswereenhancedbothfortwoseries.Comparedwithcubicperovskite,RPphasewassubjectedtosmallerimpactbyAgaddition.ThereasonsforenhancingZTvalueandthedifferentimpactfortwoseriesbyAgadditionwerealsodiscussed.
简介:Er~(3+)andLa~(3+)codopedY_2O_3nanocrystallinepowdersweresynthesizedbygelcombustionmethodandcharacterizedwiththermalanalysis,X-raydiffraction(XRD),transmissionelectronmicroscopy(TEM),high-resolutionTEM(HRTEM)techniquesandfluorescencespectroscopy.Afterbeingcalcinedat1200oC,the(Y_(1–x)La_x)_2O_3:Er~(3+)powderswereconfirmedtobecubicY_2O_3phasewiththecrystallinegrainsizeintherangeof20–40nm.TheEr~(3+)emissionat1.53μmfromthe~4I_(13/2)→~4I_(15/2)transitionwasobserved,whichwasfoundtobeenhancedbyintroducingLa~(3+)ions.SuchenhancementcouldbeattributedtotheadjustmentofEr~(3+)ions'localenvironmentbythecodopingofLa~(3+)ions,leadingtotheincreasedgroundstateabsorptioncrosssectionofEr~(3+)ions.
简介:PolycrystallineNd3+andLa3+co-dopedyttriananopowderNd3+:Y1.90La0.10O3fortransparentceramicswassynthesizedbyco-precipitationmethodusingoxalateacidastheprecipitantand(NH4)2SO4astheelectricalstabilizerunderultrasonicradiation.Nanopowderscalcinedatdifferenttemperatureswerecharacterizedwiththermalgravimetric-differentialthermalanalysis(TG/DTA),X-raydiffraction(XRD),transmittingelectronmicroscopy(TEM),energydispersivespectrometry(EDS)andspectralanalysistechniques.Th...
简介:AsystematicinvestigationofthemagneticandtransportpropertiesofTidopedLa0.67Ca0.33MnO3wasreported.TheTisubstitutionforMnionsresultsinareductioninferromagnetismandconductivity.Themetal-insulatortransitiontemperatureisclosetoCurietemperaturewhichdecreasesfrom274to82Kasxincreasesfrom0to0.17.ThemostimportanteffectofTidopingistointroducespinclustersinthesamplesduetothedistortionoflocallatticeandtheinhomogeneousmagneticstructureinducedprimarilybytherandomdistributionofMnions.Amaximummagnetoresistanceratioaslargeas90%in1Tat122Kwasobtainedforthesamplewithx=0.055,whichisfourtimeslargerthanthatobtainedforLCMOsampleat272K.Thereisaremarkablefield-historydependentMRinthecoolingprocessforthedopedsampleswhilesuchphenomenondisappearsinthewarmingrun.Theresistivityfollowswellthevariablerangehoppingbehaviorinparamagneticstate.Boththesizeeffectandspindependenthoppingofcarriersbetweenthespinclustersshouldbeconsideredinthissystem.
简介:采用溶胶喷雾干燥-煅烧还原方法制备超细/纳米W-La2O3复合粉末,将粉末压制成形后在1950℃烧结,制备La2O3弥散强化钨合金,检测合金的密度与强度,并采用SEM对超细粉末形貌、合金的组织结构、断口形貌进行分析,结果表明:随La2O3加入量增加,粉末颗粒显著细化,W-0.7%La2O3复合粉末的粒径仅为0.1μm;制备的W-La2O3超细/纳米复合粉末具有很高的烧结活性,烧结后,合金最高相对密度达到99.1%;La2O3均匀弥散分布于钨晶界,抑制钨合金的晶粒长大,提高材料的强度,W-0.7%La2O3合金中钨平均晶粒尺寸仅为8.7μm,抗弯强度达到548MPa;合金的断裂形式表现为穿晶-沿晶共有的复合断裂形式。
简介:Inthiswork,boththethermalexpansionandelectricalconductivityofnanocrystallineLa2Mo2O9werestudied.ThenanocrystallinepowderofLa2Mo2O9wasobtainedbysol-gelmethod,andwiththehelpofSHP(superhighpressure)upto4.5×104atmat700℃forashorttime,andthenanocrystallinepowderwasdensifiedwithoutobviousparticlesizegrowth.TheelectricalconductivityofnanocrystallineLa2Mo2O9wasoneorderofmagnitudelowerthanthatofthemicrocrystallinesampleatthesametemperature.Owingtothephasetransition,themicrocrystallineLa2Mo2O9hasanabruptincreaseofthermalexpansionwithapeakvalueof48×10-6K-1at556℃.Forthenanocrystallinematerial,thepeakvalueincreasesto112×10-6K-1at520℃.Ontheotherhand,above600℃thesignificantgrowthofparticlesizeofthenanocrystallineLa2Mo2O9wasobserved,accompanyingbyatremendousincreaseofthermalexpansionwithapeakvalueofthirdhigherthanthatofLa2Mo2O9.