高阻相对La2／3Ca1／3MnO3低场磁电阻效应的影响

实验研究了La2／3Ca1/3MnO3系统晶界上掺杂(YSZ)对其输运性能和磁电阻效应(MR)的影响。样品是由溶胶．凝胶法制成的。通过对样品的电输运特性的测量表明,在掺杂量(x)低于2％时,掺杂引起电阻的增大并降低了金属．绝缘体转变温度;当掺杂量高于2％时电阻逐渐减小,且转变温度增加。而低场磁电阻效应随掺杂量增加,在x=1％时达到最大。     

（1-x）La2／3Ca1／3MnO3／xCr2O3复合材料的电输运性质和磁电阻效应

用固相反应法制备了（1-x）La2／3Ca1／3MnO3/xcr2O3（x为摩尔分数）复合样品，实验研究了在外加0～3T的磁场下，Cr203含量对该复合样品的电输运性质及磁电阻的影响。结果发现随着Cr2O3含量的增加，金属．绝缘体（M-I）转变温度耳急剧降低，并且当Cr2O3，含量x〉0．1时此转变消失。与此同时，电阻率随其含量增加而快速增大，特别的是在样品中观察到了较宽温度范围内显著增强了的磁电阻。这种结果的出现可能与Cr2O3有关的新相偏析在La2／3Ca1／3MnO3（LCMO）晶界和颗粒界面有关。     

稀土空位锰氧化物(La(1-x-y)Yy)2/3Ca1/3MnO3的磁热效应

采用固相反应法制备La(1.x)2/3Ca1/3MnO3(x=0.0,0.04)和(La0.7Y0.3)2/3Ca1/3MnO3系列样品,测量不同温度下的磁化强度-磁场曲线,计算样品的磁熵变,研究La空位掺杂和Y3 离子掺杂对磁热效应的影响.结果表明,La空位掺杂(x=0.04)的样品在居里温度附近磁熵变最大值为6.22 J/(kg.K),这比La2/3Ca1/3MnO3磁熵变最大值(6.26 J/(kg.K))稍有降低;而Y3 离子掺杂的样品在温度60 K时和磁场强度2 T下,其磁熵变最大值为0.568 J/(kg.K),并且磁熵变随温度变化有继续增大的趋势.这表明(La0.7Y0.3)2/3Ca1/3MnO3可以作为一定温区的磁致冷材料.     

La_((1+x)/3)Ba_((2-x)/3)Mn_xCu_(1-x)O_3(0.8≤x≤1)晶体结构和输运性质

用固态反应法制备了名义组分为 L a(1 + x) /3Ba(2 - x) /3Mnx Cu1 - x O3(0 .8≤ x≤ 1) 的系列试样。试样结构的单相性经粉末 X射线衍射分析而得以证实 ,且随 Cu的掺杂其结构由未掺杂时的立方对称性转变为正交对称性。输运实验表明 :所有试样均经历了半导体到金属的转变 ,但转变温度 TP随掺杂量增加而逐渐移向低温端 ;外加磁场大大增加了 TP附近的导电性 ,导致 TP附近最大磁电阻效应的出现     

一价Na元素对LaMnO_3母体A位掺杂的磁电性质研究(英文)

通过测量La1-xNaxMnO3(x=0.05,0.10,0.15,0.20,0.25,0.33)体系的M-T曲线和R-T曲线,研究了La位Na掺杂对体系磁电性质的影响.结果发现:随着Na掺杂浓度的增加,体系居里温度Tc升高,顺磁-铁磁相变逐渐变陡;伴随着顺磁-铁磁相变,体系发生金属-绝缘体相变,电阻随掺杂浓度增加而下降.体系磁电性质的变化来源于掺杂引起的Mn3+-O-Mn4+间的双交换作用、静态Jahn-Teller畸变和公差因子的变化.     

二元掺杂系列La－（Ca，Ba）－Mn－O材料巨磁电阻特性研究

用固相反应法制备了二元掺杂系列La2/3(CaxBa1-x)1/3MnO3(x=0,0.40,0.45,0.55,0.60,1.0)多晶材料;在77K～420K范围内测量了样品的电阻和磁电阻。结果表明,所制备的系列样品电阻率与温度的关系具有明显的双电阻峰结构;在T=77K～350K范围内,样品均有相似的磁电阻行为:在低温区(TTC区域,电阻率、磁电阻都随温度的升高而迅速下降,样品在高温(TC附近及T>TC区域)的这一行为可用双交换(DE)模型与非磁无序来说明。通过掺杂研究发现,掺杂量x为0.55,0.60的2种样品在室温下具有较大的磁电阻,在B=1.2T时分别达到14.5%和19.5%。     

La（1＋x）／3Ba（2—x）／3MnxCu1—xO3（0.8≤x≤1）晶体结构和？…

用固态反应法制备了名义组分为Ｌａ（１＋ｘ）／３Ｂａ（２－ｘ）／３ＭｎｘＣｕ１－ｘＯ３（０．８≤ｘ≤１）的系列试样。试样结构的单相性经粉末Ｘ射线衍射分析而得以证实,且随Ｃｕ的掺杂其结构由未掺杂时的立方对称性转变为正交对称性。输运实验表明：所有试样均经历了半导体到金属的转变但转变温度ＴＰ随掺杂量增加而逐渐移向低温端;外加磁场大大增加了ＴＰ附近的导电性,导致ＴＰ附近最大磁电阻效应的出现。     

La-（Ca-Ba-Sr）-Mn-O锰氧化物高低温输运特性

用固相反应烧结法制备了多晶体材料La2/3Ca1／3MnO3(LCMO)，La2／3(Ca0.5Ba0.5)1/3MnO3(LCBMO)、La2，3Ba1/3MnO3(LBMO)，La2／3(Sr0.5Ba0.5)1/3MnO3(LSBMO)和La2/3Sr1／3MnO3(LSMO)，测量了它们在77K～800K的电阻和磁电阻特性。实验发现，通过一定的工艺技术制备出的CMR材料有强烈的相界效应，在低温下有大的磁电阻，且在Tc附近存在明显的从金属态向半导体态的转变：用自旋极化电子隧道效应和靠近居里点逾渗模型较好地解释了电阻和磁电阻行为：用非绝热小极化子跃迁模型对高温的电阻特性进行拟合处理，得到了激活能；同时发现退火处理对样品的电阻率有重要的影响。     

La_(2/3)Ba_(1/3)MnO_3∶Ag_x多晶靶材制备及其性能

采用化学共沉淀法制备了不同Ag掺杂量的La2/3Ba1/3MnO3∶Agx(x为摩尔分数,x=0.00、0.02、0.08、0.10、0.20)多晶靶材,通过XRD、SEM和R-T对La2/3Ba1/3MnO3∶Agx靶材的结构和性能进行测试分析,实验结果表明:所得样品为正交晶系钙钛矿结构;掺Ag(x=0.02、0.08、0.10、0.20)样品比未掺Ag样品的金属-绝缘转变温度Tp值低;随着烧结温度和Ag掺杂量的升高,金属-绝缘转变温度Tp随之增加;随着Ag掺杂量增加,电阻率归一化值先增大后减小。La、Ba、Mn元素的摩尔分数与理论设计的数值基本相同,O元素在烧结过程中缺失较严重,Ag元素的摩尔分数也较低,这与Ag在高温烧结时的挥发有关。     

Sr位掺Na对La0．67Sr0．33MnO3晶格结构和磁电特性的影响

采用固相反应法制备了样品La0.67Sr0.33-xNaxMnO3（x=0．05，0．10，0．15，0．20，0．25，0．33）。通过实验测出了样品的X射线衍射谱图、M-T曲线、p-T曲线和MR-T曲线，研究了Sr位掺Na对La0.67Sr0.33MnO3的晶格结构和磁电特性的影响。结果表明，样品呈菱面体结构，当x≥0．20时，Mn^3＋／Mn^4＋〈1，体系在反铁磁态，但实验中所有样品表现为顺磁-铁磁相变伴随绝缘体．金属相变；随X增加，巨磁电阻MR增大，Tc降低，当x=0．33时，在室温区获得了很大的磁电阻MR=241％。     

La1/3Sr2/3Mn1-xFexO3(x=0,0.05)中电荷有序现象的超声研究

系统研究了La1／3Sr2／3Mn1-xFexO3(x=0，0．05)单相多晶样品在20--300K温区内的电荷输运性质和超声特性，结果表明，La1／3Sr2／3MnO3样品在235K存在明显的电荷有序现象，但是极少量的Fe取代Mn就会有效地抑制电荷有序现象的发生，伴随电荷有序现象的发生声速出现极大的软化，其相对变化超过5％，这表明La1／3Sr2／3Mn1-xFexO3中存在剧烈的电-声子相互作用，分析指出该电-声子耦合主要起源于Jahn-Teller效应。     

Magnetoresistance and magnetization of La2／3 （Ca0. 60 Ba0. 40 ） 1／3 MnO3 in different temperature ranges

A polycrystalline La2/3 (Ca0. 60 Ba0. 40 ) 1/3 MnO3 was prepared by standard solid reaction method. Magnetization(M) and magnetoresistance of the sample were measured between T= 77 K and 350 K. It is found that some correlations exist in the external field dependency of the magnetoresistance magnetoresistance and M in the low and high temperature regions. Moreover, there are different magnetic field dependence of magnetoresistance and magnetization in different temperature ranges, which indicates the presence of different magnetoresistance mechanisms.Based on the models of spin-polarized tunneling and percolation model, the simulated magnetoresistance obtained using Monte Carlo method well explains the experimental fact.     

Low-field magnetoresistance of (1-x)La_(0.6)Dy_(0.1)Sr_(0.3)MnO_3/0.5x (Sb_2O_3) composite system under different sintering temperatures of matrix

A series of (1-x)La0.6Dy0.1Sr0.3MnO3/0.5x(Sb2O3)(x=0.15) samples were prepared by the solid-state reaction method, and the influence of sintering temperature of the matrix on low-field magnetoresistance of (1-x)La0.6Dy0.1Sr0.3MnO3/0.5x (Sb2O3) was studied through the measurements of X-ray diffraction (XRD) patterns, scanning electron microscope (SEM) image, resistivity-temperature (ρ-T) curves, and magnetoresistance-temperature (MR-T) curves. The results indicate that for the samples with low sintering temp...     

Si4+和F-掺杂对LiNi1/3Co1/3Mn1/3O2结构和电化学性能的影响

以Li2CO3、NiO、Co2O3、MnO2、LiF和SiO2为原料,采用机械力活化固相法制备了Si4+和F-掺杂的锂离子电池正极材料LiNi1/3Co 1/3Mn1/3O2.通过X射线衍射(XRD)、扫描电镜(SEM)和电化学性能测试等技术研究了LiNi1/3Co1/3Mn1/3O2的结构特征、形貌及电化学性能等.结...     

La0.67Sr0.33Co1-xFexO3体系的输运行为

研究了Co位Fe掺杂对La0.67Sr0.33Co1-xFexO3体系的电输运性质和巨磁效应的影响.结果表明:电阻率在低掺杂(x≤0.1)时显示金属性输运行为,而在高掺杂(x=0.2,0.3)时则显示半导体行为.而且,Fe掺杂削弱了Tc处的MR峰值,但增加了低温下T≤Tc的MR值.La0.67Sr0.33Co1-xFexO3体系的磁电阻的起源可由外加磁场导致的自旋态转变来解释.     

Structural, magnetic and magnetotransport properties of La0.8Sr0.2MnO3/xLaMnO3 composites

The effect of LMO doping on the structure, magnetic and magnetotransport properties of La_0.8Sr_0.2MnO₃ (LSMO)/xLaMnO₃ (LMO) has been investigated. Two types of LSMO/xLMO composites, named as SL_x (low temperature sintered samples) and SH_x (high temperature sintered samples) samples, were prepared by different sintering temperature and solid-state reaction method. The presence of LMO at the grain boundaries increases the disordered states at the surface of the grains and therefore the magnetization and transition temperature decrease by increasing the amount of LMO doping level. Results show that the rate of decreasing of transition temperature is much more for high temperaure sintered samples. Also the resistivity of samples increases by the increase of LMO doping level. Results also show that the LMO doping has an effect on a low field magnetoresistance (LFMR). The value of LFMR increases for low doping level of 0 ≤ x ≤ 15, for SL_x samples and 0 ≤ x ≤ 10 for SH_x samples. Also LFMR decreases at high doping level. The spin dependent tunneling and scattering at the interfaces of the grain boundaries are responsible for the increase of LFMR at low doping level, while reduction of LFMR at high doping level may result from the grain boundary becoming too thick for electron tunneling.     

Effect of calcination temperature on characteristics of LiNi1/3Co1/3Mn1/3O2 cathode for lithium ion batteries

LiNi1/3Co1/3Mn1/3O2 was synthesized by sol-gel method and effect of calcination temperature on characteristics of LiNi1/3Co1/3Mn1/3O2 cathode was investigated. The structure and characteristics of LiNi1/3Co1/3Mn1/3O2 were determined by XRD, SEM and electrochemical measurements. The results show that the compound LiNi1/3Co1/3Mn1/3O2 has layered structure with hexagonal lattice. With the increase of calcination temperature, the basicity of the material decreases, and the size of primary particle rises. The LiNi1/3Co1/3Mn1/3O2 calcined at 900 ℃ for 12 h shows excellent electrochemical performances with large reversible specific capacity of 157.5 mA-h/g in the voltage range of 2.75-4.30 V and good capacity retention of 94.03% after 20 charge/discharge cycles. Capacity of LiNi1/3Co1/3Mn1/3O2 increases with enhancement of charge voltage limit, and specific discharge capacities of 179.4 mA.h/g, 203.1 mA.h/g are observed when the charge voltages limit are fixed at 4.50 V and 4.70 V, respectively.     

Al2O3/Cu复合材料强化机理研究

采用内氧化法制备了Al2O3／Cu复合材料，进行了高温电子拉伸实验，并通过微观组织观察，分析了该复合材料的强化机理。拉伸实验结果显示：Al2O3／Cu复合材料不仅室温强度很高，而且高温时仍保持较高的强度。微观组织观察分析表明：细小的Al2O3颗粒的弥散分布是该复合材料具有高强度的主要原因，表现在：Al2O3颗粒存在能够抑制Cu基再结晶的进行；Al2O3颗粒的存在阻碍晶界亚晶界运动，从而阻碍晶粒长大；Al2O3颗粒的阻碍位错运动，增加位错密度；Al2O3颗粒的存在提高材料的蠕变抗力。