Synthesis of La_xK_(1–x)CoO_3 nanorod and their catalytic performances for CO oxidation

A series of Lax K1–x CoO3 nanorod oxides with perovskite structure were synthesized by sol-gel method using polyvinyl alcohol(PVA) as additive.These perovskite-type complex oxide catalysts were characterized by the techniques of X-ray diffraction(XRD),infrared(IR),Brumauer-Emmett-Teller(BET) and scanning electron microscopy(SEM).And the results showed that nanorods of La1–x Kx CoO3 perovskite-type complex oxides were fabricated by sol-gel method when the mass concentration of PVA was 4% and the calcined temperature kept at 700 ℃ for 4 h.The catalytic results of CO oxidation showed that the Lax K1–x CoO3 catalysts had high activity.LaCoO3 nanorods exposed more {110} plane than LaCoO3 nanoparticles,which was beneficial to the catalytic oxidation of CO.LaCoO3 nanorods had the best catalytic performance for the oxidation of CO.At 200 oC,the CO conversion could reach 100%.     

La_(1-x)Gd_xTiO_3和La_(1-x)YxTiO_3系的某些磁学性质

La_1-xGdxTiO_3和 La_1-xYxTiO_2系化合物表现出一种临界温度对成份的不寻常关系。对 X>0.5,Tc 随 X 减小而减小,对 X<0.5,Tc 随 X 增加而增加,相当好地确定了 X=0那部分的特征。YTiO_3是铁磁性半导体(Tc=29K),而 GdTiO_3能描述为2种亚点阵的亚铁磁体(Tc=34K),它也是半导体。LaTiO_3是金属的并且是弱铁磁性的(Tc=125K)。表明中间部分有比末端部分更复杂的磁有序的证据,和随 X 减小将发生半导体向金属特性的转     

Synthesis and characterization of calcium and manganese-doped rare earth oxide La_(1-x)Ca_xFe_(0.9)Mn_(0.1)O_(3-δ) for cathode material in IT-SOFC

In order to develop novel cathode materials with high performance for intermediate temperature SOFC(IT-SOFC),Ca and Mn doped rare earth oxides La1-xCaxFe0.9Mn0.1O3-δ(x=0.1,0.3 and 0.5,denoted as LCFM9191,LCFM7391 and LCFM5591) were synthesized by solid state reaction(SSR) method.The formation process,phase structure and microstructure of the synthesized samples were characterized using thermogravimetry/differential scanning calorimetry(TG/DSC),X-ray diffraction(XRD) and scanning electron microscopy(SEM).The thermal expansion coefficients(TEC) of the samples were analyzed at 100-900 oC by thermal dilatometry.The electrical conductivities of the samples were measured with direct current(DC) four-terminal method from 300 to 850 oC.The results indicated that the samples(x=0.1 and 0.3) exhibited a single phase with orthorhombic and cubic perovskite structure,respectively after being sintered at 1200 oC for 3 h.The electrical conductivity of the samples increased with temperature up to a maximum value,and then decreased.The small polaron hopping was regarded as the conducting mechanism for synthesized samples at T≤600 oC.The negative temperature dependence occurring at higher temperature was due to the creation of oxygen vacancies for charge balance.LCFM7391 had higher mixed conductivity(>100 S/cm) at intermediate temperature and could meet the demand of cathode material for IT-SOFC.In addition,the average TECs of LCFM9191 and LCFM7391 were 11.9×10-6 and 13.1×10-6 K-1,respectively,which had good thermal match to the common electrolytes.     

Preparation and Physicochemical Characterization of La_(1-x)Ce_xCoO_(3 δ) Perovskite Catalyst and Its Methane Catalytic Combustion

Methanecatalyticcombustionhasattractedmanyconcernsinrecentyearsbecauseofitshighefficiency ,lowenergycost ,lownitrogenoxidesemissions ,andlongtimestableoperationinleanburncondi tions[1～ 6 ] .MethanewhichisrichinChinaisthemaincomponentofnaturalgas .Successfulresearchandde velopmentofadvancedmethanecombustioncatalyticmaterialsisveryhelpfultoaddresstoday′sseriousen vironmentandenergyproblems .Oxidationcatalystsforexhaustedemissioncontrolaremainlynoblemetalsbecauseoftheirhighcatalyticactivity .H…     

Transport Properties of Rare Earth Manganese Oxide La_(0.67)Ca_(0.33)Mn_(1-x)Fe_xO_3

CompoundsofthetypeLn1-xAxMnO3(Ln =rareearth ,A =Ca ,Ba ,Sr ,etc .)havebeenthepopularsubjectsofextensiveresearchrecently ,mainlyduetotheexistenceofcolossalmagnetoresistance(CMR ) [1～ 3] .Atroomtemperature ,theperovskitecompoundLnMnO3isantiferromagneticinsulatorwhereMnistrivalent .ThepartialsubstitutionoftrivalentLnionswithdivalentionssuchasCa ,Ba ,Sr ,andPbetc .yieldsanewcompoundexhibitingstrongferro magnetismandhighmetallicconductivity .Thetrans portpropertyinthesecompoundscanbepartly…     

Solid state reaction synthesis and total electrical conductivity of La_(0.7)Sr_(0.3)Cr_yMn_zCo_(1-y-z)O_(3-δ)

The La0.7Sr0.3CryMnzCo(1-y-z)O3-δ samples were prepared by solid state reaction.The phases,microstructure and properties of the samples were investigated by XRD,SEM,DC four-probe method and iodometry method.The single orthorhombic phase La0.7Sr0.3CryMnzCo(1-y-z)O3-δ perovskite oxides were obtained when sintered at l350 °C for 10 h.The oxygen nonstoichiometry of the materials varied inversely with the total electronic conductivity.The sample with composition of La0.7Sr0.3Cr0.5Mn0.35 Co0.15O3-δ had the maximal total electronic conductivity and the lowest oxygen nonstoichiometry which were 22.4 S/cm and 0.040 at 850 °C,respectively.The low total electronic conductivity is related to the low relatively density of the samples directly.The activation energy of conduction changed at 550 °C,and the activation energy of conduction at high temperature(T550 °C) was higher than that at low temperature range(T550 °C).     

Fabrication of low-resistance LaNi_xO_(3+δ) thin films for ferroelectric device electrodes

LaNiO_3 thin films with different La/Ni ratios were deposited on Si substrates by sol-gel process. The electrical resistivities of LaNi_xO_(3+δ) films with different La/Ni ratios were measured by four-probe method.LaNi_(0.95)O_(3+δ) thin film has the lowest resistivity. First-principle calculations show that LaNi_(0.95)O_(3+δ) has the largest Ni-O-Ni bond angle and the shortest Ni-O bond length, which means LaNi_(0.95)O_(3+δ) has the strongest metallic property, hence, the electrical resistivity is the lowest. Au/PZT(PbZr_(0.52)Ti_(0.48)O_3)/LaNi_xO_(3+δ) and Au/PZT/Pt ferroelectric capacitors were fabricated to evaluate LaNi_xO_(3+δ) as a bottom electrode. It is shown that fatigue properties of PZT films can be significantly improved by using LaNi_xO_(3+δ) instead of Pt as the bottom electrode. The Ⅰ-Ⅴ test results of PZT films show that LaNi_(0.95)O_(3+δ) as bottom electrode can reduce the threshold voltages of PZT films, suggesting that La/Ni ratio in LaNi_xO_(3+δ)has a large influence on the film properties.     

Preparation of Sr_2Fe_(1-x)Sc_xMoO_(6-δ) nanopowders and its electrical conductivity

Double-perovskite Sr2Fe1-xScxMoO6-δ (x=0, 0.05, 0.1, 0.2, 0.3, 0.4) powders applied to the cathode of solid oxide electrolysis cells were synthesized by the sol-gel citrate combustion method. Initial powders were calcined at different temperatures under different atmosphere (air, H2(4 vol.%)/Ar), and the effects of the preparation process on the structure and the morphology of the powders were investigated by thermal analysis (TG/DSC), X-ray diffraction (XRD), scanning electron microscopy (SEM) and surface area analysis. The electric conductiv-ity of the materials was measured by electrochemical work station using wafers prepared by dry pressing. It was found that the formation of perovskite structure was related to the content of Sc and combustion improver (NH4NO3), pH value, calcining temperature and atmosphere. A single perovskite phase of Sr2Fe1-xScxMoO6-δ could be formed after 3 h calcining in reducing atmosphere of H2 (4 vol.%)/Ar at 1100 oC. The electrical property indicated that, this material had a potential to be used in medium/high temperature solid oxide fuel cells or electrolysis cells.     

Transport and Magnetic Properties of Perovskite-Type Manganite (La_(0.8-x)Ce_x Sr_ (0.2))_ (0.97)MnO_3

Transport and Magnetic Properties of Perovskite-Type Manganite (La_(0.8-x)Ce_x Sr_ (0.2))_ (0.97)MnO_3     

La_(0.4)Ca_(0.6)Mn_(1-x)Ga_xO_3体系的电荷有序相

用固相反应法制备La0.4Ca0.6Mn1-xGaxO3(x=0,0.08,0.10,0.12,0.15)系列多晶样品。通过X射线衍射(XRD)图谱、电阻率-温度(ρ-T)曲线、磁化强度-温度(M-T)曲线和电子自旋共振(ESR)图谱,研究Ga3+替代Mn3+对La0.4Ca0.6Mn1-xGaxO3体系电荷有序相的影响。结果表明,当Ga掺杂量高达15%时电荷有序相仍然没有被破坏。这是因为Ga3+是非磁性离子,而La0.4Ca0.6MnO3是CE型反铁磁电荷有序相结构,Ga3+替代Mn3+只是仅仅起到把体系中的长程自旋序破坏为短程自旋序的作用,同时随Ga替代量增大,Mn3+与Mn4+的比远离双交换的最佳摩尔配比(Mn3+∶Mn4+=2∶1),不利于双交换,因而非磁性的Ga3+替代Mn3+难以破坏La0.4Ca0.6MnO3的电荷有序相。     

La_(0.9)Rb_(0.1)Co_(1-x)Fe_xO_(3-δ)钙钛矿催化剂上NO_x辅助碳烟燃烧性能的研究

通过柠檬酸溶胶凝胶法制备了La_(0.9)Rb_(0.1)Co_(1-x)Fe_xO_(3-δ)(x=0.1～0.8)系列钙钛矿催化剂。通过X射线衍射(XRD)、氢气程序升温还原(H_2-TPR)、NO_x程序升温脱附(NO_x-TPD)及X射线光电子能谱(XPS)考察了Fe含量变化对催化剂结构、NO_x辅助碳烟燃烧反应活性、催化剂氧化还原活性、催化剂表面Fe和Co的化学状态以及NO_x储存能力的影响。结果表明:所制备的催化剂均保持钙钛矿结构,Co与Fe的共掺杂改变了B位金属的化学状态,催化剂表面存在Co~(2+)和更高价态的Fe物种。相比纯LaCoO_3和LaFeO_3,La_(0.9)Rb_(0.1)Co_(1-x)Fe_xO_(3-δ)(x=0.1～0.8)催化剂碳烟燃烧的特征温度T_(50)分别下降约30和70℃,碳烟燃烧的速度也随之加快。同时,在NO_x辅助碳烟燃烧过程中,NO氧化所生成的NO_2可与碳烟反应生成N_2,其中La_(0.9)Rb_(0.1)Co_(0.6)Fe_(0.4)O_(3-δ)催化剂具有最高的NO_x消除能力,在381℃时达到36.4%。     

钙钛矿氧化物Eu_(1-x)Sr_xCoO_(3-δ)的结构和性能

以固相反应法合成了钙钛矿型复合氧化物Eu_(1-x)Sr_xCoO_(3-δ)(x=0.1,0.3,0.5,0.7)材料。研究了各样品的晶体结构、化学状态和电输运性能,测试了样品在不同温度下的直流电导率。结果表明,合成样品都呈类钙钛矿结构,在低温段,载流子具有p型小极化子导电特征,同时,样品随着掺杂比例的变化晶格氧变化较大,Eu0.5Sr0.5CoO3-δ氧空位浓度最大,氧输运性能较好,是较好的固体氧化物燃料电池阴极材料。     

Research of Colossal Magnetoresistance in La_(0.67)Ca_(0.33)Mn_(1-x)Cr_xO_3 (0.00x0.15)

Inthelastfewyears ,agreatdealofworkhasbeendevotedtothemixed valencemanganitesLn1-yAyMnO3(Ln =rareearthelements ,A =Ca ,Sr ,Ba)exhibitingcolossalmagnetoresistance (CMR ) [1～ 3] .Aprominentfeatureofthesematerialsisametallic insu latingtransitionassociatedwiththeferromagnetic paramagnetictransition .Earlyworkhadrevealedthesignificanceofthedouble exchangeinteractionthroughMn3 O Mn4 networkintheclosecorrelationbe tweenthetransportandthemagnetism[4 ,5] .However ,recentdetailedstudieshaves…     

La_(0.67)Ca_(0.33)Mn_(1-x)T_xO_3低场下的大磁阻效应

研究了在低磁场 H≤ 0 .8T区间下的材料 L a0 .6 7Ca0 .33Mn1 - x Tx O3( T=Fe或 Ni)中的磁阻效应 ,发现在L a0 .6 7Ca0 .33Mn1 - x Fex O3中用铁替代锰降低了磁阻比 ,但改善了磁阻随磁场变化的线性度。用少量的镍替换锰 ( x=0 .1)时 ,可得到较好的低场高磁阻变化特性     

MnO_x/Ce_(0.5+x)Zr_(0.4–x)La_(0.1)O_(1.95)-Al_2O_3 catalysts used for benzene catalytic combustion

Complete oxidation of benzene over supported manganese oxides catalysts was studied.Composite supports Ce0.5+xZr0.4–xLa0.1O1.95-Al2O3 (x=0,0.1,0.2,0.3,0.4),and CeO2-Al2O3 were prepared by co-precipitation method,and manganese oxides (MnOx) catalysts were prepared by incipient wetness method.Catalytic activity was performed in a conventional fixed bed flow reactor.Among these catalysts,MnOx supported on Ce0.8Zr0.1La0.1O1.95-Al2O3 was found to have the highest catalytic activity for benzene oxidation.The comp...     

Giant Low-Field Magnetoresistance in Polycrystalline La_(2/3)Ca_(1/3)Mn_(1-x)Cu_x O_3 Sintered at 1100 ℃

Themixed valenceperovskitemanganiteRE1-yAyMnO3(RE =rareearth ,A =alkalineearth)systemisoneofthemoststudiedtopicsduetoitsunusualmagneticandtransportproperties ,especiallythecolossalmagnetoresistance (CMR)effect[1,2 ] .CMRisfoundonamagneticfieldscaleofseveralteslas ,whichisnotveryappealingforapplications .Accord ingly ,manyresearchgroupsfocusedontheinvestiga tionofextrinsicmagnetoresistanceeffectsfoundinvar iousmagneticoxides[3,4 ] ,sincethesepromisedalargemagnetoresistanceratioinlowfields …     

钙钛矿锰氧化物(La_(1-x)Gd_x)_(0.5)Sr_(0.5)MnO_3的电磁特性

通过磁化强度和电阻的测量对多晶样品(La1-xGdx)0.5Sr0.5MnO3(x=0,0.1,0.2,0.3,0.4)的电磁特性进行了系统的实验研究。当x≤0.2时,样品显示出铁磁金属态(FMM)到顺磁绝缘态(PM I)的转变;当0.3≤x≤0.4时,金属-绝缘体转变温度Tp消失,样品显示出反铁磁绝缘态(AFM I)到顺磁绝缘态(PM I)的转变。同时随着x的增加所有样品的居里温度Tc和金属-绝缘体转变温度Tp都降低,并且在居里温度附近观测到了磁电阻效应。     

Ce_(1–x)La_xO_y solid solution prepared from mixed rare earth chloride for soot oxidation

Ce_(1–x)La_xO_y solid solution was simply prepared using mixed rare earth chloride(RECl_3·x H_2O, RE=Ce, La99%, containing unseparated Ce and La from rare earth metallurgical industry) as precursor by ultrasonic-assisted co-precipitation method with different ultrasonic frequencies(CLf, f=200, 400, 600, 800, 1000 Hz). A compared Ce_(1–x)La_xO_y solid solution(CL*) was also prepared by the same mothod with 10% less precipitant. X-ray diffraction results confirmed the formation of Ce1–xLaxOy solid solution, and the crystal structures of these catalysts were not very sensitive to ultrasonic frequency and precipitant amount. However, both of the factors had obvious effect on morphology and surface area of CL, and precipitant amount seem to play a more crucial role than ultrasonic frequency for Ce_(1–x)La_xO_y solid solution preparation. When soot and catalyst were tight contacted, the peak temperature(Tpeak) of soot oxidation and oxygen reducing temperature for CLf catalysts decreased linearly with increasing surface area. Under loose contact condition, the Tpeak had obvious negative correlation with H_2 consumption. It was inferred that good reducibility of the Ce_(1–x)La_xO_y solid solution favored the soot oxidation reaction. The Ce_(1–x)La_xO_y solid solution prepared from unseparated rare earth chloride showed a good soot oxidaiton activity. Controlling the preparation conditions to prepare a CL catalyst would high surface area will enhance its reducibility and activity.     

Cerium and ruthenium co-doped La_(0.7)Sr_(0.3)FeO_(3-δ) as a high-efficiency electrode for symmetrical solid oxide fuel cell

Symmetrical solid oxide fuel cells(SSOFCs) could be alternative energy conversion devices due to their simple fabrication process and low cost.Herein,perovskite La_(0.6)Ce_(0.1)Sr_(0.3)Fe_(0.95)Ru_(0.05)O_(3-δ)(LCSFR) was synthesized and evaluated as a high-performance electrode for SSOFCs based on the electrolyte of La_(0.9)Sr_(0.1)Ga_(0.8)Mg_(0.2)O_(3-δ)(LSGM).LCSFR retains their stable perovskite crystal structure in both reducing and oxidizing atmospheres,though a minor amount of LaSrFeO_4 phase is present under reducing conditions.Morphology investigation shows that homogeneously dispersed Ru metallic nanoparticles are exsolved on the surface of LCSFR after being reduced.The polarization resistance(R_p) of LCSFR-CGO(Ce_(0.9)Gd_(0.1)O_(2-δ)) is about 0.11 Ω·cm~2 at 800℃ in air,while the value of R_p for LCSFR-CGO in wet H_2(3% H_2 O) increases up to 0.32 Ω·cm~2.The symmetrical LCSFR-CGOILSGMILCSFR-CGO cell demonstrates a performance with an open circuit potential(OCV) of 1.07 V and a maximum peak power density of 904 mW/cm~2 at 800℃ using wet H_2 as the fuel.This high performance indicates that LCSFR is a candidate electrode for SSOFCs.     

Pr_(1-x)(La_(0.37)Ce_(0.63))_xCoO_3的制备及催化活性探究

采用溶胶—凝胶法制备了Pr_(1-x)(La_(0.37)Ce_(0.63))_xCoO_3,利用TG-DSC、FT-IR分析前驱体的分解特性和化学键变化规律,结合XRD、SEM-EDS检测粉体微观结构、形貌以及元素分布;通过CV、LSV和RRDE技术探讨粉体在碱性溶液中氧还原ORR电催化活性。结果表明,在700℃下焙烧,x0.4时,有La_2O_3、CeO_2杂相出现,x0.4时钙钛矿晶体结构消失,x=0.4时得到的纯相粉体呈多孔结构。与商用Pt/C相比,Pr_(1-x)(La_(0.37)Ce_(0.63))_xCoO_3粉体质量活性(质量比电流)是其1.7倍,达到172.54mA/mg,而半波电位较低仅为0.60V(vs.RHE)。以二电子发生氧化还原反应过程中,副产物H_2O_2产率为77%,作为催化材料有待进一步改性。