Nd0.5Sr0.5Mn1−x(Gax, Tix)O3 体系中的电荷有序与自旋有序

通过磁化强度和电子自旋共振（ESR）测量，研究了Nd_0.5Sr_0.5Mn_1−x(Ga_x, Ti_x)O₃(0.04≤x≤0.4)体系的磁特性.发现用少量Ti替代Mn就完全破坏了系统的电荷有序(CO)相,并诱导出团簇自旋玻璃相,这显示了一个CO的坍塌和自旋有序(SO)相增强的过程.然而,用Ga替代Mn将导致系统CO 相的融化.研究还发现,随着Ga替代的增加,CO相逐渐被抑制,但残留的CO相总是存在;而且在低温区反铁磁(AFM)CO相和铁磁(FM)SO共存.此外,我们还观察到磁化强度-温度(M-T)曲线中磁化强度的急剧上升,并把这个反常现象归因于CO区域内从倾斜的AFM SO到FM SO的相变.     

用激光分子束外延在Si衬底上外延生长La1-xSrxMnO3单晶薄膜

采用SrO和SrTiO3作为缓冲层, 用激光分子束外延在Si (100)衬底上成功地外延生长出La_1-xSr_xMnO₃ (x=0.1, 0.2, 0.3) (LSMO)单晶薄膜. 锐而清晰的反射式高能电子衍射仪 (RHEED)的衍射条纹和持久的RHEED强度振荡, 表明LSMO薄膜是很好的二维层状外延生长. X射线衍射和高分辨透射电镜分析结果证明, 在Si基底上获得了很好外延生长的LSMO薄膜, LSMO薄膜为C取向的单晶薄膜. 并在室温条件下观测到很好的LSMO/Si p-n结I-V整流特性.     

Crystal Structures and Magnetic Properties of La0.9Sb0.1Mn1-xTixO3(x＝0,0.05,0.10,0.15,0.20)

采用固相反应法制备了钙钛矿锰氧化物La09.Sb0.1Mn1-xTixO3(x＝0,0.05,0.10,0.15,0.20)的多晶样品.X射线衍射(XRD)表明,样品仍为正交钙钛矿结构.扫描电镜(SEM)观测结果表明,随着掺杂量的增加,晶胞体积增大,间隙增大,但仍为规则的立方晶格结构.所有样品在598-606cm-1范围内出现了红外吸收光谱.且随着掺杂量的增加,光谱向高频移动.样品的磁电阻(MR)表明对材料进行B位微量掺杂,对提高其磁性质有明显作用.     

镧系收缩对(La0.8Ln0.2)2/3Ca1/3MnO3纳米粉体结构和电输运性质的影响

 用溶胶-凝胶法制备了系列掺杂(La_0.8Ln_0.2)_2/3Ca_1/3MnO₃(Ln=La,Ce,Pr,Nd,Sm,Eu,Gd,Dy,Ho,Er)纳米级晶体.对于所制备系列样品在同一实验条件下的测试发现,在La位被其他镧系元素部分替代后,平均晶格常数和容差因子也存在类似镧系收缩的单方向变化：随着替代原子Ln原子序数的增加,平均晶格常数a呈减少趋势,平均晶格常数b基本未发生变化,而平均晶格常数c总体来说略呈减少趋势;容差因子t在0.925～0.918之间逐渐减少,但体系仍保持钙钛矿结构.不同掺杂元素样品表面形貌和电输运行为差异很大,各样品颗粒粒度分布在30～800nm范围,转变温度在82～194K范围.铈组(La,Ce,Pr,Nd,Sm,Eu)掺杂样品的转变温度未呈现单一某一方向的变化,而钇组(Gd,Dy,Ho,Er)掺杂样品的金属-绝缘体转变温度随着原子序数的增加而增高,此变化方向的单一性与镧系收缩单一性相协调.     

Kinetics of C2(a3Πu) radical reactions with NO, N2O, O2, H2 and NH3

Pulsed laser photolysis/laser-induced fluorescence (LP-LIF) is utilized to measure rate constants for C₂(a³Π_u) reactions with NO, N₂O, O₂, H₂ and NH₃. Multiphoton dissociation of C₂Cl₄ at 266 nm is employed for the generation of C₂(a³Π_u) radicals. The C₂(a³Π_u) concentration is monitored by the fluorescence of the (0, 0) band of the (d³Π_g&#8596;a³Π_u) transition at 516.5 nm. C₂(a³Π_u) removal rate constants for the reactions are determined as k_NO = (5.46 ± 0.10) × 10^-11 cm³ molecule^-1 s^-1 , k_N2O = (1.63 ± 0.20) × 10^-13 cm³ molecule^-1 s^-1 , k_N2O = (1.58 ± 0.16) × 10^-11 cm³ molecule^-1 s^-1, k_O2 = (5.92 ± 1.00) × 10^-14 cm³ molecule^-1 s^-1, k_H2< 1.0× 10^-14 cm³ molecule^-1 s^-1. Based on the data analysis and theoretical calculation, we suggest that the C₂(a³Π_u) reactions with H₂ and NH₃ proceed via the hydrogen abstraction mechanism, barriers exist at the entrance channel of the reactions of C₂(a³Π_u) with H₂ and NH₃.     

Synthesis and crystal structure of the trimetallic erbium tetrahydride complex [Li(THF)4][{(ButCp)2Er(μ-H)} 3-(μ3-H)]

Reaction of [(Bu′tCp)2Er(μ-CI)]2 with Bu′Li in 1:1 molar ratio in THF at -78℃, after work-up, afforded the trimetallic erbium tetrahydride complex [Li(THF)4][{(Bu′Cp)2Er(μ-H)}3(μ3-H)] (1) by β-hydrogen elimination reaction. Crystal structure determination reveals that complex 1 has discrete ion pair structure. The anion is composed of three (Bu′Cp)2Er units to form a triangle array connected by three bridged hydrogen atoms, and the fourth hydrogen atom coordinated to three Er^3 ions. The coordination num-ber for each Er^3 ion is 9.     

(La0.9Dy0.1)2/3Ba1/3Mn1-xAlxO3(x=0,0.05)氧化物的结构与磁性

【目的】为改善(La_(0.9)Dy_(0.1))_(2/3)Ba_(1/3)Mn_(1-x)Al_xO_3的磁热性能,研究掺杂Al对其晶体结构、居里温度、相变类型以及磁热性能的影响。【方法】采用固相反应法制备锰氧化物(La_(0.9)Dy_(0.1))_(2/3)Ba_(1/3)Mn_(1-x)Al_xO_3(x=0,0.05)样品,利用X射线衍射法分析样品的结构,用振动样品磁强计测量样品的磁性。【结果】所制备样品均为单相钙钛矿结构,属于菱方晶系,空间群为R-3c(No.167)。掺杂Al使样品居里温度由无掺杂的274K降低到248K,在外加磁场变化为20kOe时最大磁熵变由2.16J/(kg·K)降低到1.85J/(kg·K)。样品的铁磁-顺磁相变属于二级相变。采用双交换作用机制解释了居里温度和磁化强度的变化。【结论】非磁性元素Al替代Mn不改变其晶体结构,稍微降低了锰氧化物的磁热性能。     

预合成对Li1/2Ln1/2TiO3(Ln=Sm,Nd)微波介电性能的影响

研究了在不同的预合成和烧结条件下,Li1/2Ln1/2TiO3(Ln=Sm,Nd)的微波介电性能．当Ln=Sm,预烧温度为1000℃,烧结温度在1200～12500℃,样品的微波介电性能好．典型值为εr=52,Qf=2280GHz;当Ln=Nd,烧结温度在1200～12500ε,预烧温度为1000ε或950℃的样品εr、Qf值较高,典型值为εr=80,Qf=2100GHz．     

The concentration quenching characteristics of 5D3-7FJ and 5D4-7FJ (J=0―6) transitions of Tb3+ in YBO3:Tb3+ phosphor

The photoluminescence quenching behaviors of ^5D3-^7Fj and ^5D4-^7Fj （J = 0—6） transitions of Tb^3＋ in YBO3：Tb under 130—290 nm excitation were systematically investigated. The results revealed that the quenching concentrations of both ^5D3-^7Fj and ^5D4-^7Fj transitions of Tb^3＋ in YBO3：Tb were mainly dependent on excitation wavelength. Particularly, the quenching concentrations of ^5D4-^7Fj transitions of Tb^3＋ under 130—290 nm excitation were correlated with excitation bands of YBO3：Tb. The quenching concentrations of ^5D3-^7Fj transitions remained at low concentration （2%） under 186—290 nm excitation and then increased gradually with energy of incoming excitation photon when excited at 130—186 nm. This dependence should be involved in their excitation mechanisms and quenching pathway in particular excitation region.[第一段]     

Microstructures and mechanical properties of as-extruded Mg–5Sn–1Zn–xAl(x=1, 3 and 5) alloys

As-extruded Mg–5Sn–1Zn–xAl alloys(x=1, 3, and 5) were fabricated by hot extrusion. The experimental results revealed that the yield strength of alloys initially decreased and then increased with the increase of Al content. These changes were mainly attributed to the difference in crystallographic texture and volume fractions of second phases. The ultimate tensile strength, yield strength, and elongation of the alloys were greater than 310 MPa, 227 MPa, and 11%, respectively. The strain hardening ability of the alloys was also discussed.     

Colossal magnetoresistive p-n junctions of perovskite oxide La0.9Sr0.1MnO3／SrNb0.01Ti0.99O3

We have successfully fabricated the colossal magnetoresistive (CMR) p-n junctions of perovskite oxide La0.9Sr0.1MnO3/SrNb0.01Ti0.99O3 (LSMO/SNTO) with laser molecular beam epitaxy. The I-V characteristics of the LSMO/SNTO p-n junctions as a function of applied magnetic field (0—5 T) were studied between 100 and 300 K. We found that the p-n junction exhibited the CMR behavior. The CMR ratio △R/R0 (△R = RH - R0) is positive in magnetic fields below 0.13 T and at high temperature, while it displays a negative CMR near 100 K and in magnetic fields over 0.13 T. The CMR ratio values are 8% at 0.1 T and 13% at 5 T and 300 K, 40% at 0.1 T and 150 K, 10% at 0.13 T and -60% at 5 T and 100 K. The CMR behavior of the p-n junction is different from those of the LaMnO3 compound family.     

巨磁电阻材料La0.85MnO3的低频内耗和电磁性能

用低频扭摆法在多功能内耗仪上测量了自掺杂巨磁电阻材料La0.85MnO3的温度内耗谱.结果表明内耗峰位不随频率的变化而变化,但峰高和频率成反比且对应的内耗峰处模量有明显变化,这说明对应的内耗峰处的变化是由某种相变引起的.内耗、电阻及磁化率曲线的对应关系,说明该材料出现了顺磁-铁磁转变和半导体-金属转变,所伴随的结构变化导致了内耗峰的出现.     

La0.8Sr0.2Mn0.86Fe0.14-xCoxO3微波吸收性能研究

用溶胶-凝胶法制备了La0.8Sr0.2Mn0.86Fe0.14-xCoxO3（x=0.01,0.02,0.03）粉晶, 用XRD表征了其晶体结构,用微波网络矢量分析仪测量了样品在2-18GHz频率范围内的复介电常数和复磁导率,根据测量数据计算了微波反射率与频率的关系曲线。研究结果表明,样品都有一个吸收峰,峰高及位置随x不同而异,其中样品La0.8Sr0.2Mn0.86Fe0.13Co0.01O3,厚度为1.80mm时,吸收峰高27.9dB,2-18GHz吸收带宽5.3GHz;厚度为2.00mm时,吸收峰高26dB, 2-18GHz吸收带宽4.9GHz。从电、磁损耗角正切看,样品既有介电损耗又有磁损耗,但介电损耗要大于磁损耗。     

La_(0.7)Ba_(0.3)Mn_(1-x)Fe_xO_3的巨磁电阻效应及磁性

采用溶胶－凝胶工艺制备Ｌａ０．７Ｂａ０．３Ｍｎ１－ｘＦｅｘＯ３化合物．研究其磁性、导电性和磁电阻效应．结果表明,随着Ｆｅ含量的增加,电阻率增加,铁磁居里温度近似线性下降     

(La0.9Bi0.1)NiO3的制备及其热电性能

以硝酸盐为原料、柠檬酸为络合剂、无水乙醇为溶剂,采用溶胶-凝胶法获得(La0.9Bi0.1)NiO3的纳米前驱体,在800℃下煅烧该前驱体2 h得到单相的(La0.9Bi0.1)NiO3纳米级粉末.利用XRD、TG-DTA、SEM等手段对其结构进行表征,所得到的(La0.9Bi0.1)NiO3颗粒大约为50 nm.在空气气氛中1 000℃下烧结6 h获得多晶的(La0.9Bi0.1)NiO3陶瓷样品.对(La0.9Bi0.1)NiO3陶瓷材料的微观结构进行分析,并对其室温到700℃的热电性能进行研究.热电测试结果表明,(La0.9Bi0.1)NiO3是N型热电材料且具有一定的热电性能.     

Sm(CobalFe0.1CuxZr0.033)7.4(x=0.06,0.08,0.10)永磁体的磁性能

以粉末冶金法制备了2∶17型Sm(Cobal Fe0.1 CuxZr0.033)7.4 (x=0.06,0.08,0.10)永磁体,研究了Cu含量对Sm(Cobal Fe0.1CuxZr0.033)7.4永磁合金的退磁曲线、磁能积、矫顽力、矫顽力温度系数等的影响.结果发现,Cu含量超过0.08以后会导致磁体的退磁曲线方形度降低,并进而导致磁体的磁能积降低;同时发现提高Cu含量,有利于提高2∶17型Sm(Cobal Fe0.1CuxZr0.033)74永磁体的室温及高温500℃的矫顽力,但高Cu含量也会导致矫顽力温度系数增大,使矫顽力在高温下衰减较快,这表明2∶17型SmCo永磁体的矫顽力与Cu元素的微化学成分分布密切相关.     

羰基铁/La1-xSrxMnO3（x=0.3,0.4）复合物的制备及微波吸收性质研究

用溶胶凝胶法合成了La1-xSrxMnO3(x=0.3,0.4)纳米颗粒,并用物理混合的方法合成了不同重量比例的羰基铁/La1-xSrxMnO3复合物样本,研究了复合物的结构,形貌及微波吸收性质.研究结果表明:复合物中羰基铁与La1-xSrxMnO3颗粒的比例显著地影响着复合物的吸波性质.当复合物中羰基铁与La0.6Sr0.4MnO3颗粒的重量比达到30∶1时,复合物的吸波性能达到最佳值,这可能归功于复合物的介电性能和磁性能在此种状态下达到匹配平衡.     

Structure and composition-dependent optical properties of (PbxSr1-x)TiO3 (x=0.4, 0.6) nanotube arrays

Lead strontium titanate(Pb_xSr_(1-x))TiO_3(x=0.4,0.6) nanotubes were synthesized by sol-gel template method via spin coating.The structures and morphology of the as-prepared samples were characterized by X-ray diffractometry.scanning electron microscopy and transmission electron microscopy.X-ray photoelectron spectroscopy was used to determine the chemical composition of the sample and the valence state of elements.Raman spectroscopy of the as-prepared(Pb_xSr_(1-x))TiO_3(x=0.4,0.6) nanotubes at room temp...     

纳米晶LaCoO3和La1—xSrxCoO3的制备及其催化氧化性能研究

研究发现以Ｎａ２ＣＯ３－ＮａＯＨ为沉淀剂,结合超临界干燥法,是合成纳米晶ＬａＣｏＯ３及Ｌａ１－ｘＳｒｘＣｏＣＯ３（其中ｘ≤０．３）的有效途径。以此法可制得平均粒径约１５ｎｍ的ＬａＣＯ３和平均粒径约３５ｎｍ的Ｌａ０．８Ｓｒ０．２ＣｏＯ３．ＬａＣｏＯ３对ＣＯ的催化氧化活性随粒径的减小明显提高,纳米晶ＬａＣｏＯ３中镧被锶部分取代可显著提高对ＣＯ氧化的催化活性。     

La3-xYxMgNi14(x=0～2)贮氢合金的相结构与电化学性能研究

系统研究了La3-xYxMgNi14(x=0,1.0,1.5,2.0)贮氢合金的相结构和电化学性能.结构分析表明,合金均由Gd2Co7和Ce2Ni7型结构相组成.随Y含量值x的增加,Gd2Co7型相的丰度增加,Ce2Ni7型相的丰度减少.合金各相的晶胞参数(a,c)和晶胞体积(V)均随x的增加而线性减小.电化学研究表明,随着Y含量的增加,合金电极最大放电容量减小,活化性能显著降低.合金随x的增加,HRD值减小与合金电极电催化活性及氢在合金相中的扩散速率的减小有关.