非化学计量(La0.6Dy0.1Sr0.3)1-xMnO3的电输运及MR温度稳定性机制研究

用固相反应法制备了非化学计量的(La0.6Dy0.1Sr0.3)1-xMnO3(x=0.00,0.10,0.20,0.30,0.35)系列样品,通过XRD、ρ-T曲线、MR-T曲线,研究电输运及磁电阻(MR)温度稳定性的机制。XRD检测表明,非化学计量的(La0.6Dy0.1Sr0.3)1-xMnO3在1200℃下烧结24 h,实际形成了La0.6Dy0.1Sr0.3MnO3钙钛矿相和Mn2O3相组成的二相复合体材料。电输运性质均表现出绝缘体-金属相变,ρ-T曲线高温区出现尖峰,较低温区出现"肩峰",是钙钛矿体相内双交换作用和晶界处电子自旋极化隧穿引起的电阻率共同作用的结果。MR-T表现出,在高温区出现磁电阻峰,在低温区随温度降低磁电阻持续增大,表现出低场磁电阻特征,在中间温区出现磁电阻的温度稳定性,用La0.6Dy0.1Sr0.3MnO3钙钛矿颗粒体相产生的本征磁电阻与颗粒界面效应产生的隧穿磁电阻的叠加给出解释。x=0.30的样品,0.8 T磁场下,在258 K～198 K温区,产生的磁电阻为(6.3±0.2)%。     

CuO复合对La0.80Sr0.05K0.15MnO3电输运和磁电阻的影响

用固相反应法制备了(1-x)La0.80Sr0.05K0.15MnO3/xCuO(x=0.00,0.04,0.08,0.10,0.20,0.30)二相复合体。通过X射线衍射图谱、扫描电子显微镜照片检测结构,表明形成完好的钙钛矿相和CuO相,CuO分布在钙钛矿颗粒之间,形成对钙钛颗粒的包覆。通过测量零场和加场下的电阻率-温度曲线以及磁电阻-温度曲线,研究电输运性质及磁电阻效应,结果表明,CuO复合对La0.80Sr0.05K0.15MnO3电输运和磁电阻效应影响很大。在高温区出现磁电阻峰,表现出本征磁电阻特征,在低温区随温度降低磁电阻持续增大,表现出由界面引起的隧穿磁电阻特征,总的磁电阻是本征磁电阻与隧穿磁电阻的迭加,在中间温区出现磁电阻的温度稳定性。     

La2/3Ca1/3MnO3/xTiO2复合磁性材料的磁电特性研究

采用溶胶-凝胶法制备La2/3Ca1/3MnO3纳米级磁性颗粒和TiO2胶体,按一定比例制成La2/3Ca1/3MnO3/xTiO2(其中x取0、0.1、0.2、0.3、0.4)复合磁电阻材料。用XRD谱确定样品的晶体结构。采用振动样品磁强计测量了样品的磁滞回线和场冷却磁化强度随温度的变化行为;采用标准四引线法测量样品在恒定磁场下的电阻率随温度的变化。实验测量结果表明体系的磁化强度、剩磁、矫顽力随TiO2含量的变化具有相似的规律,具有室温的居里温度;并且当磁场强度小于0.4T时,磁电阻与磁场平方成正比关系;当大于0.6T时,磁电阻与磁场成线性关系。     

双层锰氧化物La1.2Sr1.8Mn2O7单晶的磁性和电性研究

通过浮区炉方法制备钙钛矿双层锰氧化物单晶材料La1.2Sr1.8Mn2O7,利用X射线衍射、劳埃衍射确定单晶的质量;选择高质量的单晶片切割成长方形,用超导量子磁强计测量其磁性;采用四端法测量其输运性质。XRD测量表明,La1.2Sr1.8Mn2O7粉末为单相。磁性测量表明,在高温区域样品的磁化强度很小,表现为顺磁态,在T=110 K附近磁化强度迅速增大,并且随温度的降低逐渐达到饱和,显示出铁磁性的特征。磁电阻的测量显示出单晶样品缺陷比多晶样品少,电阻率非常小。     

镧改性固体催化剂SnO2-WO3/La2O3的制备及其催化性能

500℃焙烧3 h条件下制备了摩尔比nSn∶nW=2∶1,含3.0%(质量分数,下同)La2O3的镧改性固体催化剂SnO2-WO3/La2O3,采用IR分析对其进行了表征。通过改变催化剂用量、30%H2O2用量、反应时间及催化剂重复使用性等因素,系统考察了该稀土改性双金属氧化物催化氧化环己酮合成己二酸的催化性能。实验结果表明,己二酸的适宜合成条件为:100 mmol环己酮,1.25 g催化剂SnO2-WO3/La2O3,50 mL 30%H2O2,回流反应7 h,目的产物己二酸收率达77.7%。SnO2-WO3/La2O3连续使用6次己二酸收率仍可接近40%。     

高活性PtMo_2C/Al_2O_3催化剂的研究进展

叙述了高活性PtMo2C/Al2O3催化剂的制备、性能和在水气位移反应中的应用。由于制备出的PtMo2C/Al2O3催化剂中,其铂离子呈几个纳米分散态显微结构,分布十分均匀,它比传统的催化剂如CuZn/Al2O3、Pt/C、Pt/Al2O3和PtCeO2等的催化活性高,选择性好,WGS速率高,反应温度低。     

Al_2O_3La_2O_3Y_2O_3/Cu复合材料的电弧侵蚀特性研究

采用喷射沉积和内氧化法制备出Al2O3La2O3Y2O3/Cu复合材料,研究该材料在直流20 V/20 A的工作条件下触点的电弧侵蚀特性,并与Al2O3/Cu材料进行了对比分析.利用电子天平、扫描电镜等方法分析电弧侵蚀后触点的质量变化和表面微观结构.结果表明,通过添加Y2O3、La2O3稀土氧化物颗粒,可有效降低触头材料的材料转移量.Al2O3La2O3Y2O3/Cu材料的抗熔焊性和抗烧损性优于Al2O3/Cu材料的性能.在直流阻性负载条件下Al2O3La2O3Y2O3/Cu阳极触头表面形成凹坑,阴极触头表面形成凸起,触点表面显示出浆糊状凝固物和喷发坑等电弧侵蚀形貌特征.     

La2O3-Mo阴极材料中La2O3稳定性研究

本文采用高温光电子能谱方法对La2O3-Mo阴极及碳化La2O3-Mo阴极材料表面La2O3的化学稳定性进行了研究。实验结果表明,La2O6并不具备文献报道的极好的化学稳定性。材料中的La2O3在高温、真空条件下,其部分晶格氧发生分离。La2O3可以被Mo2C还原成单质La。单质La的结合能高于La2O3的结合能。实验证实单质La3d5／2的结合能为835．96eV,并首次给出La3d3／2的结合能实验数值为852．23eV。     

La2/3(CaXBa1-X)1/3MnO3材料的绝缘体-金属转变与晶界效应

用固相反应法制备了La2/3(CaxBa1-x)1/3MnO3(x=0.00,0.40,0.45,0.55,0.60,1.00)六种多晶CMR材料,并测量了在77K～350K范围内零磁场和0.4T外磁场下的电阻率。这些样品都出现了双电阻峰结构,采用Mott转变表达式ρ～exp(T0/T)1/4拟合了实验数据,结果表明高温峰的转变是绝缘体-金属(I-M)转变,而低温峰不是I-M转变峰,用自旋极化电子隧道效应和局域化模型解释了电阻和磁电阻行为。此外,在x=0.4～0.6掺杂范围内样品呈现出异常的电阻行为。     

高分子凝胶法制备纳米ZnO/La2O3及光催化性能

以Zn(CH3COO)2·2H2O,AgNO3为原料,丙烯酰胺为单体,N,N'-亚甲基双丙烯酰胺为网络剂,采用高分子凝胶法在550℃下制得纳米ZnO/La2O3.通过XRD物相分析,得知沉积稀土氧化物La2O3的ZnO纳米粒子样品的物相均是六方晶系纤锌矿结构;TEM形貌观察,粒子基本为球形,纳米ZnO/La2O3的平均粒径约为26 nm,红外光谱分析高分子的分解程度,在550℃时分解完全.水溶液中次甲基蓝染料在ZnO/La2O3半导体光催化条件下,pH值为9时,能迅速分解,在降解90 min时,次甲基蓝的降解率达到81%.     

Study on BSTO/MgO Ferroelectric Materials for Phase Shift Doped with Rare Earth Oxides

Phasedarrayantennascansteerthetransmitted orreceivedsignalswiththeadvantagesoffastscan ning,multipletargetstrackingandgoodanti jam ming.Theseantennasarecurrentlyconstructedusing ferritephaseshiftingelements,whicharecostly,large andheavy.Therefore,theirmil…     

The self-fulfilling prophecy in close relationships: rejection sensitivity and rejection by romantic partners

The authors hypothesized a self-fulfilling prophecy wherein rejection expectancies lead people to behave in ways that elicit rejection from their dating partners. The hypothesis was tested in 2 studies of conflict in couples: (a) a longitudinal field study where couples provided daily-diary reports and (b) a lab study involving behavioral observations. Results from the field study showed that high rejection-sensitive (HRS) people's relationships were more likely to break up than those of low rejection-sensitive (LRS) people. Conflict processes that contribute to relationship erosion were revealed for HRS women but not for HRS men. Following naturally occurring relationship conflicts, HRS women's partners were more rejecting than were LRS women's partners. The lab study showed that HRS women's negative behavior during conflictual discussions helped explain their partners' more rejecting postconflict responses.     

Current-voltage characteristics with several threshold currents in insulating low-doped La1-xSrxMnO3 (x=0.10) thin films

The current-induced resistive switching behavior in the micron-scale pillars of low-doped La0.9Sr0.1MnO3 thin films using laser molecular-beam epitaxy was reported. It was demonstrated that the current-voltage curves at 120 K showed hysteresis with several threshold currents corresponding to the switching in resistance to metastable low resistance states, and finally, four closed loops were formed. A mode was proposed, which was based on the low-temperature canted antiferromagnetism ordering for a lightly doped insulating regime.     

Effects of La~（3＋） on osteogenic and adipogenic differentiation of primary mouse bone marrow stromal cells

In order to elucidate the action of La3+ on bone metabolism,effects of La3+ on the osteogenic and adipogenic differentiation of pri-mary mouse bone marrow stromal cells(BMSCs) were studied by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide(MTT) test,alkaline phosphatase(ALP) activity measurement,mineralized function,oil red O stain and measurement.The results showed that La3+ pro-moted the proliferation of BMSCs except at 1×10-10 and 1×10-6 mol/L.The effect of La3+ on the osteogenic differentiation depended on con-centrations at the 7th day,but the osteogenic differentiation was inhibited at any concentration at the 14th day.La3+ promoted the formation of mineralized matrix nodules except at 1×10-8 and 1×10-5 mol/L.La3+ inhibited adipogenic differentiation except at 1×10-10 and 1×10-7 mol/L at the 10th day,and inhibited adipogenic differentiation except at 1×10-9 mol/L at the 16th day.These findings suggested that La3+ might have protective effect on bone at appropriate dose and time.This would be valuable for better understanding the mechanism of the effect of La3+ on bone metabolism.     

Effect of La_2O_3 on the wear behavior of MoSi_2 at high temperature

Wear behaviors of MoSi2 doped with La2O3 against SiC under different loads at 1000 oC in air were investigated by using an XP-5 type high temperature friction and wear tester. The worn surfaces and phases of the samples were analyzed by scanning electron microscopy (SEM) and X-ray diffraction, respectively. Results showed that the addition of La2O3 could obviously improve wear resistance of MoSi2. Because of the formation of MoO3 phase on the worn surface, La2O3/MoSi2 composite mainly exhibited oxidation and abrasive wear, which was different from the wear form of MoSi2 such as adhesion, oxidation and abrasion.     

Electrochemical Preparation of La—Fe Alloy Films in Dimethylsulfoxide（DMSO）

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Partial Oxidation of Methane to Syngas over Monolithic Ni/γ-Al2O3 Catalyst——Effects of Rare Earths and Other Basic Promoters

A series of monolithic Ni/γ-Al2O3 catalysts with and without basic promoters (Na, Sr, La, Ce) were prepared. Partial oxidation of methane (POM) to syngas was carried out in a continuous-flow, fixed-bed reactor. The influences of reaction conditions, including temperature, CH4/O2 ratio and space velocity, on the performance of the catalyst were investigated. The results show that at a high space velocity of 1×105 h-1, optimal CH4 conversion can be obtained. Effects of promoters such as Na, Sr, Ce, La were also investigated, and the catalyst samples were characterized by means of temperature-programmed reduction and XRD techniques. XRD suggests that the addition of promoters has no influence on the crystal structure of Ni/γ-Al2O3 catalyst. The results show that the addition of a small amount of promoters improves the reducibility and activity of the catalyst. The side reaction CH4 2 O2→CO2 H2O, is fully restrained and 100% H2 selectivity is achieved when Ce and La are used as promoters, respectively.     

Synthesis kinetics and thermophysical properties of La_2（Zr_（0.7）Ce_（0.3））_2O_7 ceramic for thermal barrier coatings

La2(Zr0.7Ce0.3)2O7 (LZ7C3) ceramic was synthesized by solid state reaction with La2O3, ZrO2 and CeO2 as starting materials. The synthesis kinetics, phase structure, mass loss and microstructure were studied by thermo gravimetric-different thermal analyzer (TG-DTA), X-ray difference (XRD) and scanning electron microscopy (SEM). The thermal conductivity and thermal expansion coefficient were measured by laser-flash method and pushing-rod method, respectively. XRD results showed that LZ7C3 was a mixture of La2Zr2O7 (LZ, pyro- chlore) and La2Ce2O7 (LC, fluorite). The lowest synthesis temperature and time of LZ7C3 were 1400 oC and 5 h. There were no peaks of La2O3 when the powder granularity was about 0.82 μm in the synthesis process. The atom ratio La:Zr:Ce of prepared LZ7C3 powder was very close to 10:7:3 which was the theory value of LZ7C3. The thermal conductivity of LZ7C3 decreased gradually with the temperature increased up to 1200 oC, and was located within 0.79 to 1.02 W/(m·K), which was almost 50% lower than that of LZ, whereas its thermal expansion coefficient was larger and the value was 11.6×10-6 K-1.     

Influence of [La(EDTA)]~- on pore structure of activated alumina carrier at high-temperature

The activated alumina as a catalyst carrier were widely used in automotive exhaust catalysts under high temperature,such as,petroleum refining catalysts,hydrogenation and hydrodesulfurization catalyst carrier in China and abroad.γ-Al2O3 was the catalyst carrier that was the most widely used and the best carrier of improved specific surface area .However,the activation of the coating consisted of γ-Al2O3 were usually transformed into α-Al2O3 at 800 oC,causing increased density,reduced specific surface area,and the collapse result of pore structure.While the temperature reached 1200 oC,activation of coating detached from the carrier,the resistance of flowing gas increased,catalytic activity decreased.Addition of La2O3 stabilized the γ-Al2O3 crystal structure,which would keep the activation stability of coating at a high temperature and inhibit activity loss.The activated alumina carrier treated with the solid-pore-expanding agent containing [La(EDTA)]-that synthesized using solid and solid-hybrid approach with the thermal stabilizer lanthana and EDTA at the high-temperature had a 10-30 μm large pore porous network-like structure,after alumina was calcined at 1200 oC for 1 h.The specific surface area of four specimen were beyond 120 m2/g,while the sample specific surface area of x([La(EDTA )]-)=1% was up to 150.36 m2/g.