掺K~+和Ag~+的LaMnO_3的室温庞磁电阻效应

采用固相烧结法制备了名义成分为 La1- x Kx Mn O3(x=0 .1～ 0 .4)和 La0 .8K0 .2 - yAgy Mn O3(y=0～ 0 .2 )的多晶样品 ,发现用 K、Ag取代 La后 ,可使菱面体结构的这种钙钛矿型稀土锰氧化物居里温度升高至室温附近 ,从而使样品的室温磁电阻增大 ,其中 La0 .8K0 .2 Mn O3在μ0 H =1 T磁场下的磁电阻可达 1 3.5%。该值比单纯掺 Na和掺 Ag的同样成分的稀土锰氧化物的磁电阻要大。通过对磁电阻与磁化强度之间密切关系的讨论 ,探讨了磁电阻效应的微观机理     

非正分钙钛矿化合物(La0.8Sr0.2)0.7MnO3的磁电阻效应

采用固相反应法制备了名义成分为(La0.8Sr0.2)0.7MnO3的多晶钙钛矿锰氧化物,通过电阻率、磁化曲线和居里温度的测量,对其磁性与磁电阻效应进行了研究。样品近似呈La0.8Sr0.2MnO3/Mn3O4两相复合结构。其电阻率随温度的变化曲线具有双峰特征,特别是其磁电阻比在一个较宽的温区内(220~320K)基本上保持不变,相对正分样品La0.8Sr0.2MnO3而言,非正分样品磁电阻比的温度稳定性大大提高,这一特性也表明了其作为磁电阻传感器材料的可行性。     

La_(0.60)Sr_(0.30-y)Na_(0.10)MnO_3(y=0,0.05,0.10,0.15)系列材料的磁电阻效应

利用溶胶-凝胶法(sol-gel)制备了稀土锰氧化物La0.60Sr0.30-yNa0.10MnO3(y=0,0.05,0.10,0.15)多晶样品。通过扫描电子显微镜(SEM)、物理性质测量系统(PPMS)研究了样品的颗粒形貌、尺寸和电输运性质。结果表明,样品颗粒基本呈球形,平均颗粒大小为100nm;在Sr位引入适量空位后,室温附近所有样品庞磁电阻效应有了明显的改善。特别是y=0.15的样品,在1.8T的磁场下,其磁电阻比峰值为19.0%,相应的峰值温度为328K且其CMR值在270~305 K的温区范围内均保持在8.5%(±0.5%)左右,温度稳定性有显著改善。这些结果对庞磁电阻材料的应用研究有一定意义。     

Na、K、Ag掺杂对La_(0.60)Sr_(0.40)MnO_3材料晶体结构、磁性和电输运性质的影响

利用溶胶-凝胶法制备了稀土锰氧化物La0.60Sr0.40-xNaxMn O3(x=0、0.10、0.15、0.20、0.30、0.33、0.35)、La0.60Sr0.40-xKxMn O3(x=0、0.15、0.20、0.30)、Agδ-La0.60Sr0.40-xAgx-δMn O3(x=0、0.15、0.20、0.25、0.30)系列多晶样品。研究发现Na+、K+、Ag+取代部分Sr2+后,当掺杂量x≥0.15时,Na、K、Ag系列样品的晶胞体积均随掺杂量x增加而单调变大,样品居里温度随Na、K、Ag掺杂量x的增加而降低;当Na、K、Ag含量较小时,三个系列样品的电阻率峰值随掺杂量x的增加而减小,当x0.20时,样品的电阻率峰值随x的增加而增大。对其微观机理进行了讨论,认为相对于替代离子半径,Mn4+与Mn3+离子对数目之比Rn是影响材料以上性质的主要原因。     

(1-x)La0.6Dy0.1Sr0.3MnO3/（x/2）（Sb2O3）复合体系磁电阻及其温度稳定性

用固相反应法制备了纯La0.6Dy0.1Sr0.3MnO3和(1-x)La0.6Dy0.1Sr0.3MnO3/(x/2)(Sb2O3)样品,研究了样品的电输运性质及高温磁电阻温度稳定性。结果表明,零场下,纯La0.6Dy0.1Sr0.3MnO3的ρ-T曲线出现双峰现象,高温峰是本征峰,较低温出现"肩峰"是非本征峰,复合体系在较低温的"肩峰"消失,用晶界效应予以解释;样品的电输运机制是,母体La0.6Dy0.1Sr0.3MnO3用ρ=ρ0+AT2拟合比较合理,复合样品用ρ=ρ0+AT2.5拟合比较合理;复合样品的MR-T曲线在高温出现一个平台,本征与非本征磁电阻的竞争结果是在高温区出现磁电阻平台,实现了高温区磁电阻的温度稳定性。     

(La1-xTbx)2/3Sr1/3MnO3薄膜的巨磁电阻效应

利用脉冲激光沉积法制备了（La1-xTbx)2/3Sr1/3MnO3系列薄膜样品。在77－300K的温度范围内,对样品的微观结构、磁化强度、电阻率和巨磁电阻效应等物理性质进行了系统研究。随着Tb含量x的增大,铁磁－顺磁转变温度随之下降,在x=0. 33样品中,最大磁化场μ0H=1.2T时,观察到34％的巨磁电阻。本文对其机理进行了研究和讨论。     

La0.7-xSmxSr0.3MnO3体系的磁电性质和磁致伸缩效应

用固相反应法制备了La0.7-xSmxSr0.3MnO3(x=0、0.1、0.2、0.3、0.4、0.5、0.6)多晶材料,研究了它们的磁电性质及室温下的磁致伸缩效应.结果表明,随着Sm掺杂量的增加,样品的晶体结构从菱面体相转变为正交相,居里温度下降.在结构转变点附近,样品室温磁致伸缩效应出现极大值.样品在室温下的磁致伸缩主要来源于材料中的交换磁致伸缩.     

La0.67-xBixSr0.33MnO3化合物多孔陶瓷样品的微结构与CMR效应

用固相反应法制备了钙钛矿型氧化物La0．67-xBixSr0．33MnO3(x=0，0．1，0．2)多孔陶瓷样品，研究了这些化合物的电磁性质和CMR效应j实验结果显示，Bi有助于晶粒的长大，并使电阻率峰值向低温方向移动。多孔样品的MR主要取决于显微结构，在0-300K温度范围内MR随温度升高单调下降。在较高的温度下观察到了低场磁电阻(LFMR)效应。与多晶致密样品相比，化合物多孔样品的电阻率峰变宽，峰值下降。     

Ba0.5Sr0.5Co0.8Fe0.2O3-δ-Ag复合阴极材料的性能研究

为发展中温固体氧化物燃料电池(IT-SOFC)的阴极材料,用柠檬酸络合法合成了Ba0.5Sr0.5Co0.8Fe0.2O3-δ(BSCF)粉体,并在BSCF中加入一定量的金属Ag作为SOFC的阴极材料.X-ray衍射方法研究了复合阴极Ba0.5Sr0.5Co0.8Fe0.2O3-δ-xAg (BSCF-xAg,x=0％～30％质量分数)系列样品的成相情况,结果表明Ba0.5Sr0.5Co0.8Fe0.2-O3-δ(BSCF)和Ag二者在烧结过程中没有发生反应.高温电阻测试表明复合阴极材料(BSCF-xAg)比纯BSCF材料具有较高的电导率,BSCF-10％Ag的最大电导率在430℃达到24.3 S/cm,而BSCF的最大电导率在450℃,为19.1 S/cm.同时用交流阻抗法研究了BSCF-xAg复合阴极材料的性能,实验结果表明:Ag的参杂量为20％时,阴极极化电阻最小,在650℃BSCF的极化电阻为0.465 Ω·cm2,而BSCF-20％Ag的电阻仅为0.099 Ω·cm2,约为BSCF的1/5.这标志着参杂Ag的BSCF作为中低温固体氧化物燃料电池的阴极材料是非常具有发展前景的.     

碱性锌-空气电池阴极催化剂的制备及其性能

采用溶胶-凝胶法(Sol-gel)制备系列复合氧化物La0.8Sr0.2Mn1-xNixO3(0≤x≤1)做锌空气电池阴极催化剂。用X射线衍射(XRD)、扫描电镜(SEM)和粒度分布测试对催化剂粉末样品进行表征,结果表明样品为钙钛矿结构,平均粒径D50为4～7mm。通过阴极电位线性扫描对样品的电化学性能进行了研究,结果发现,在碱性溶液中La0.8Sr0.2Mn1-xNixO3对氧还原有良好的电催化活性,表明它们适合作碱性锌-空气电池阴极催化剂。     

二氧化锰结构参数与嵌Li+和H+的行为

H+与Li+在γ-MnO2中的嵌脱行为是由其结构(缺陷)参数决定的.不同晶型的二氧化锰或晶型相同而制备条件不同的二氧化锰,具有不同的结构参数.介绍了有利于嵌脱H+和Li+的γ-MnO2结构(缺陷)参数,结构参数与γ-MnO2在碱液中的还原机理,以及如何控制制备条件,使之具有某种结构参数等.     

Ce3+:LiCaAlF6 crystal for high-gain orhigh-peak-power amplification of ultraviolet femtosecond pulses and newpotential ultraviolet gain medium: Ce3+:LiSr0.8Ca0.2AlF6

To develop high-peak-power ultrashort pulse laser systems in the ultraviolet region, a large Ce³⁺:LiCaAlF₆ (Ce:LiCAF) crystal, a tunable ultraviolet laser medium with large saturation fluence and broad gain spectrum width, was grown successfully with a diameter of more than 70 mm. To demonstrate high small signal gain, a four-pass confocal amplifier with 60 dB gain and 54 μJ output energy was constructed. Chirped pulse amplification (CPA) in the ultraviolet region was demonstrated using Ce:LiCAF for higher energy extraction. A modified bow-tie-style four-pass amplifier pumped by 100-mJ 266-nm 10-Hz pulses from a Q-switched Nd:YAG laser had 370-times gain and delivered 6-mJ 290-nm pulses. After dispersion compensation, the output pulses can be compressed down to 115 fs. This is the first ultraviolet, all-solid-state high-peak-power CPA laser system using ultraviolet gain media, and this demonstration shows further scalability of the Ce:LiCAF CPA system. Additionally, a new gain medium, Ce³⁺ :LiSr_0.8Ca_0.2AlF₆, with longer fluorescence lifetime and sufficient gain spectrum width over 18 nm was grown to upgrade this system as a candidate for a final power amplifier gain module     

1865140型(LiMn2O4+LiNi1/3Co1/3Mn1/3O2)/Li4Ti5O12电池的性能

使用锰酸锂(LiMn2O4)、镍钴锰酸锂(LiNi1/3 Co1/3Mn1/3O2)混合正极材料和钛酸锂(Li4 Ti5 O12)负极材料,制备了中倍率1865140型锂离子电池.制备的电池在12 min内可充满电池容量的80％以上,且电池表面温度不超过35℃;在室温下以2.00 C循环1 200次,容量保持率高于91％;在高温55℃下以1.00 C循环1 000次,容量保持率高于82％.FreedomCAR混合脉冲功率特性表明:在放电深度(DOD) 10％ ～ 70％内、10s脉冲充放电状态下,电池的阻抗都在9 mΩ以下;50％DOD时的10s放电比功率为372 W/kg,充电比功率为520 W/kg.     

Cryogenic Yb3+-Doped Solid-State Lasers

Cryogenically cooled solid-state lasers promise a revolution in power scalability while maintaining a good beam quality because of significant improvements in efficiency and thermo-optic properties. This is particularly true for Yb lasers because of their relatively low quantum defect and relatively broadband absorption even at cryogenic temperatures. Thermo-optic properties of host materials, including thermal conductivity, thermal expansion, and refractive index at low temperature, are reviewed and data presented for YAG (ceramic and single crystal), GGG, GdVO₄, and Y₂O₃. Spectroscopic properties of Yb:YAG and Yb:LiYF₄ (YLF) including absorption cross sections, emission cross sections, and fluorescence lifetimes at cryogenic temperatures are characterized. Recent experiments have pushed the power from an end-pumped cryogenically cooled Yb:YAG laser to 455-W continuous-wave output power from 640-W incident pump power at an of M² 1.4.     

Highly efficient diode-pumped 3-μm Er3+:BaY2F8 laser

A systematic investigation on a series of monoclinic Er³⁺ :BaY₂F₈ crystals with different dopant concentrations (C_Er=5%-30%) and crystal orientations was conducted to optimize the laser performance in this new 3-μm laser medium by laser diode pumping. The highest slope efficiency of 32% near the quantum defect (35%) was obtained with a 10% doped Er³⁺:BaY₂F₈ crystal with the orientation (010) and a length of 3.5 mm. A maximum output power of 160 mW was achieved at an absorbed pump power of 550 mW at a wavelength of 970 nm     

尖晶石相Li1+xMn2O4及LiAl0.1Mn1.9O4-yFy的循环性能

用高温固相法制备了尖晶石相Li1+xMn2O4及LiAl0.1Mn1.9O4-yFy锂离子电池正极材料.电性能测试表明,Al、F共掺杂能提高LiMn2O4的容量.LiAl0.1 Mn1.9O4-yFy(y=0.05、0.10)常温下的初始容量分别为104.4 mAh/g和105.3mAh/g,高于Li1+xMn2O4;100次循环后,容量仍高于Li1+xMn2O4.Li1+xMn2O4(x=0.05、0.06和0.07)的高温(55℃)循环性能较好,100次循环后,容量衰减率分别为24.02%、21.78%和22.23%,除Li1.04Mn2O4(x=0.04)外,均低于LiAl0.1Mn1.9O4-yFy.阴离子的掺杂提高了材料的容量,阳离子掺杂抑制了Jahn-Teller效应,增强了尖晶石结构的稳定性,提高了材料的循环性能.     

Studies on Electrical Properties and Magnetoelectric Effect of (x)Ni0.8Cu0.2Fe2O4 + (1?x)Ba0.8Pb0.2Ti0.8Zr0.2O3 Composites

Materials consisting of piezomagnetic and piezoelectric phases viz. Ni_0.8Cu_0.2Fe₂O₄ and Ba_0.8Pb_0.2 Ti_0.8Zr_0.2O₃ have been prepared by standard ceramic method. The presence of two phases in the composites has been confirmed by XRD. Variation of the dielectric constant with frequency in the range 100–1 MHz has been studied at room temperature and the variation of dielectric constant with temperature at set frequencies (1 kHz, 10 kHz, 100 kHz and 1 MHz) has been studied. The dielectric relaxation was observed for the compositions with tetragonal structure whereas normal behaviour was observed for cubic structure. All the samples have shown linear magnetoelectric conversion in the presence of a static magnetic field. The dc resistivity (ρ_DC) was studied as a function of temperature in the range 300–773^∘K. The variation of resistivity with temperature shows metal/seconductor behaviour.     

Li1+xV3O8的结构及制备方法的研究进展

综述了Li1+xV3O8的结构特点及充放电过程中物相的变化;讨论了充放电过程的机理及影响因素;介绍了高温固相法、水热合成法、溶胶-凝胶法、液相反应法等制备方法,并比较了各种方法的利弊.     

Vacuum ultraviolet emissions from the ionic excimer molecules(KrCs)+ and (HeAr)+ by low-energy electron-beamexcitation

Vacuum ultraviolet fluorescence emissions from the ionic excimer molecules (KrCs)⁺ and (HeAr)⁺ were studied in detail by low-energy electron-beam excitation, measurements were performed as a function of gas composition, gas pressure, and deposited energy in order to investigate the kinetic mechanisms of these molecules. The rate constants of the formation and competitive reactions were determined from the observed fluorescence signal decay. Estimations of the total fluorescence yield and of the gain coefficient for these molecules are given     

Simulation of limiting field behavior in electron swarms inSF6+N2 gas mixtures

Limiting field behavior of the electron swarms in SF₆+N ₂ mixtures is investigated by a Monte Carlo simulation technique. (E/N)_lim values directly obtained from the simulation are given for 5, 10, 20, 40, 60 and 80 SF₆ fractional component in the mixture together with the corresponding electron drift velocities and mean energies. Furthermore, in the E/N range of 243⩽E/N⩽606T_d, effective ionization coefficients and mean energies in SF₆+N₂ mixtures are also evaluated with fractional SF₆ contents of 0, 20, 40, 60, 80 and 100%. The simulation results obtained are compared with the available data in the literature