Transport Properties of Polycrystalline La2/3Ca1/3Mn1-xCuxO3

The infuence of Cu dopant (x) and sintering temperature(Ts) on the troansport propeties of La2/3Ca1/3Mn1-xCuxO3 series samples prepared by Sol-Gel technique was investigated.X-ray diffraction patterns show that all the samples with different Cu dopant and sintering temperatures (Ts) are of single phase without obvious latice distortion.Experimental results indicate that the insulator-metal transition temperature is diectly related to the sintering temperature and Cu dopant x.It is interesting to observe that a proper amount of Cu dompant can substantially improve magnetoresistance effects.     

Electronic transport properties of La2/3Ca1/3Mn0.98Cu0.02O3 sintered at different temperature

The sol-gel method was adopted to prepare series of La_2/3Ca_1/3Mn_0.98Cu_0.02O₃ samples sintered at different temperatures, and the structure of samples, high-temperature electrical conductive mechanism and electronic transport properties of double-peak resistance were investigated. X-ray diffraction pattern indicates that the samples are in perovskite structures and obey the Variable-Rang Hopping Mechanism of ρ=ρ ₀exp[(T ₀/T)^1/4] under high temperatures during the electrical conduction. In addition, based on the polycrystalline granular system surface and image, the reasonable explanation was given for the double-peak resistance phemomenon. Funded by the National Natural Science Foundation of China (No. 60471024)     

La1-xZnxMnO3和La2/3Sr_((1-x)/3)Znx/3MnO3的磁电输运特性

用固相反应方法制备La1-xZnxMnO3和La2/3Sr(1-x)/3Znx/3MnO3化合物。La1-xZnxMnO3在不同掺杂浓度x的研究表明:Zn2+在一定浓度范围内掺杂,具有钙钛矿结构,但掺杂浓度在50%~70%时有ZnO衍射峰,其电阻率在100 K以上随温度而下降,当掺杂浓度为x=0.3时电阻率最低。当Zn2+和Sr2+共掺而     

Magnetoresistance plateau in La2/3Ca1/3Bi x Mn1 − x O3 granular system

The effect of doping additional Bi on the magnetoresistance (MR) of La_2/3Ca_1/3B _x Mn_1−x O₃ was investigated. It is found that traditional colossal magnetoresistance (CMR) peak can only be observed in the x<0.05 samples and the peak value decreases with the increase of x, but the x≥0.05 samples show a magnetoresistance plateau above 200 K because of the presence of additional (La,Ca,Bi)-O layers. Moreover, this MR plateau is enhanced for the segregation of the La, Ca, and Bi elements. Funded by the Foundation for the Author of National Excellent Doctoral Dissertation of China (FANEDD) (No. 200233)     

La0.7Ca0.3MnO3与Al复合体系电磁输运性质的研究

研究了具有庞磁电阻（CMR）效应的锰基钙钛矿氧化物La0．7Ca0．3MnO3（LCMO）与Al复合体系的电磁输运性质．根据X射线衍射分析及电阻率与温度的关系可知,在（1-x）LCMO＋xAl（x代表物质的量）复合样品中,发现了新相Al2O3,且LCMO晶格常数和晶胞体积随Al掺量的增加而减小,同时在复合样品中出现了除对应LCMO本征金属-绝缘体转变峰TP,之外,在较低温度区域出现了另外一个转变峰TP2的现象,且复合样品转变峰T阳比LCMO本征金属-绝缘体转变峰TP1处于较宽的温度区域．经研究认为,在合成复合样品的实验过程中,既有Al被氧化为Al^3＋替代Mn^3＋的替代反应,也有Al经过高温与空气发生反应生成Al2O3,进而填隙在LCM0晶界处影响母体的电磁输运性质．本系列复合物中较宽温度区域CMR的发现为今后同类问题的研究提供了很好的实验基础．     

多晶La0.85Na0.17MnOz晶界间自旋相关的输运性质

实验研究了晶粒间弱连接和致密连接的La0.85Na0.17MnOz多晶样品的电磁性质,发现弱连接的样品和致密连接的样品在居里温度以下的输运性质显著不同,弱连接的样品从居里温度到77 K在低场下具有较大的磁电阻,而致密连接的样品在低温的磁电阻几乎为零.结合低温下的电阻率与外磁场的关系,可以得出,晶粒间的自旋相关的隧道效应对低温的低场磁电阻起着重要作用.     

空位掺杂(La(0.7-x)Y0.3)2/3Ca1/3MnO3的结构及其微观机制研究

利用标准的固相反应法在1 200℃烧结了(La(0.7-x)Y0.3)2/3Ca1/3MnO3(x=0,0.02,0.04,0.08,0.10)样品,冷却后,取出部分在1 350℃进行再烧结.利用X射线衍射(XRD)和扫描电镜(SEM)对其晶体结构及表面微观结构进行了研究.X射线衍射测量分析表明样品均为单相,单胞仍然具有正交对称性结构(空间群为Pnm a).通过扫描电镜研究表明,当化合物x=0.04时,(La(0.7-x)Y0.3)2/3Ca1/3MnO3的表面形貌表现为致密度最好.样品在1 350℃再烧结条件下,当x≤0.04时,可以大大降低样品的晶粒大小和孔隙;但当x>0.04时,再烧结对样品的晶体结构和表面微观结构影响不大.     

(La1-xYx)2/3Ca1/3MnO3体系单电子eg带宽对输运性质的影响

通过实验研究了零场下La位上Y掺杂对(La1-xYx)2/3Ca1/3MnO3(x=0.10,0.15,0.20)系统输运性质的影响.实验结果表明,所有样品高温时呈半导体导电,低温时呈金属导电;随La位上Y掺杂含量的增加,峰值电阻温度向低温方向移动,并且转变温度附近的峰值电阻大大增加.基于Zhang S的自旋-极化理论,对实验观察进行了定量分析,结果显示随La位上Y掺杂含量的增加理论曲线和实验数据符合越来越好.这表明随单电子eg带宽的变窄,自旋-极化效应逐渐加强.     

La1-xZnxMnO3和LaL2/3 Sr(1-x)/3 Znx/3 MnO3的磁电输运特性

用固相反应方法制备La1-xZnxMnO3和La2/3Sr(1-x)/3Znx/3MnO3化合物.La1-xZn MnO3在不同掺杂浓度x的研究表明:Zn2 在一定浓度范围内掺杂,具有钙钛矿结构,但掺杂浓度在50%～70%时有ZnO衍射峰,其电阻率在100 K以上随温度而下降,当掺杂浓度为x=0.3时电阻率最低.当Zn2 和Sr2 共掺而保持La3 浓度不变,即载流子浓度不变,维持Mn3 /Mn4 =2∶1,随Zn2 掺杂浓度增大,铁磁-顺磁转变温度降低,磁阻效应增大.低场磁阻效应与Zn2 掺杂浓度无关,而与温度有关;高场磁阻效应随掺杂浓度增大而增大.     

表面活性剂对制备纳米钡铁氧体的影响

在纳米材料制备中加入表面活性剂能够阻止纳米粒子的团聚,起稳定剂和分散剂作用。应用溶胶-凝胶(sol-gel)技术制备纳米钡铁氧体(BaFe12O19),对不加表面活性剂及加入表面活性剂十六烷基三甲基溴化铵(CTAB)、Triton X-100进行对比实验,讨论加入表面活性剂对试样的影响。采用红外光谱仪、X-射线衍射仪、振动样品磁强计以及场发射扫描电子显微镜对凝胶的组成,样品的晶型、磁性能、粒径分布及显微结构进行表征。研究结果表明,表面活性剂CTAB、Triton X-100的加入使产物的粒径趋于细化,且样品的磁性能有一定的提高,其中表面活性剂Triton X-100的作用更为明显。加入表面活性剂Triton X-100后制得的样品粒径分布均匀,大约分布在40~70 nm之间,饱和磁化强度(Ms)为67.80 Am2/kg,剩余磁化强度(Mr)为41.21 Am2/kg,矫顽力(Hc)为454.55 kA/m。     

共沉淀法制备LaF3表面修饰LiNi1／3C01／3Mn1／302及性能研究

以LiNi1／3CO1／3Mn1／302为正极材料,采用共沉淀合成方法制备LaF3表面修饰LiNimCo1/3Mnm02正极材料,利用X射线衍射（XRD）、扫描电镜（SEM）和电化学测试等方法对合成材料的结构、形貌以及电化学性能进行表征。结果表明：经过LaF3表面修饰的LiNi1／3C01／3Mn1／302材料保持了LiNi1／3Co1／3Mn1/302层状结构,其中LaFs表面修饰量为0．59％时,在电压为2．75-4．50V范围内,以0．3mA／cm。电流密度下经恒电流充放电测试,其首次放电比容量为172．7mAh／g,经过50周充放电循环后放电比容量为163．5mAh／g,表现出较高的初始放电比容量和良好的抗过充电性能。     

Preparation and characterization of La1-xCexFe1-y-nCoyRunO3 compounds

Since the discovery of perovskite-type oxides ascombustion catalysts in the 1970’s, a number of effortshave been devoted to extending this material by varyingit’s A or B site composition to synthesize the cata-lysts[1 -2]. Several preparation techniques, such asthermal decomposition of cyanide, hydroxides, metal-EDTA and the hydrothermal synthesis method, havebeen employed. Among them sol-gel method has manyadvantages such as a lower synthesis temperature andeasily doping etc[3]. At presen…     

Magnetism Regulation of (In_(1-x)Fe_x)_2O_3 Semiconductors Prepared by Sol-gel Method

Fe doped In2O3 samples (In1-xFex)2O3 (x=0, 0.05, 0.1, 0.2 and 0.3) on glass substrate were prepared by sol-gel method. The XRD results demonstrate that the solubility of Fe ions in In2O3 matrix is around 20%, above which impurity phase can be observed. The transmittance of the samples with x=0, 0.05, 0.1 and 0.2 are above 80% in the visible region while the transimittance of the glass is 90%. The transmittance curves slightly red-shifts as x increasing. All of the samples except x=0 are ferromagnetic at roo...     

溶胶-凝胶法制备HPMC／Si02杂化复合薄膜

采用溶胶-凝胶法（sol—gel）在聚乳酸（PLA）基膜上负载羟丙基甲基纤维素／二氧化硅（HPMC／SiO2）有机-无机杂化层,制备HPMC／Si02有杂化复合薄膜。表征和测试杂化复合薄膜的结构与性能。结果表明：当HPMC溶液体积分数为6％时,杂化复合薄膜的氧气阻隔性能比PLA薄膜的氧气阻隔性能提高了36倍,同时,杂化复合薄膜的拉伸强度优于PLA薄膜。     

Sol－Gel法制备YBa_2Cu_3O_（7－x）超细粉末研究

用柠檬酸盐作螯合剂，用氨水调节溶液的酸度，通过Ｓｏｌ－Ｇｅｌ转变制得了粒径为１００ｎｍ大小的ＹＢａ２Ｃｕ３Ｏ（７－ｘ）超细粉末，对ＹＢａ２Ｃｕ３Ｏ（７－ｘ）在合成反应中溶胶的形成和凝胶聚合过程进行了研究和探讨。Ｓｏｌ－Ｇｅｌ法制得的ＹＢａ２Ｃｕ３Ｏ（７－ｘ）超细粉末在粒度、纯度、烧结特性和超导性能上，均优于固态反应合成方法。     

Effect of La Doping on Microstructure and Ferroelectric Properties of Bi4Ti3O12 Thin Films Prepared by Sol-gel Method

The Bi4Ti3O12 and Bi3.25La0.75Ti3O12 thin films were prepared on the Pt/Ti/SiO2/Si substrate using the sol-gel method. The effect of La doping on the microstructure and ferroelectric properties of Bi4Ti3O12 films were investigated. Both the Bi4Ti3O12 and Bi3.25La0.75Ti3O12 thin films exhibited typical bismuth layered perovskite structure. The 2Pr (remanent polarization) value of Bi3.25La0.75Ti3O12 thin films is 18.6 Μc/cm2, which is much larger than that of Bi4Ti3O12 thin films. And the Bi3.25La0.75Ti3O12 films show fatigue-free behavior, while the Bi4Ti3O12 thin films exhibit the fatigue problem. The mechanism of improvement of La doping was discussed.     

Nd0．7Ce0．3MnO3的电脉冲诱导电阻转变特性及其溶胶-凝胶制备方法

以醋酸盐为原料、采用溶胶-凝胶法制备Nd0.7Ce0．3MnO3薄膜材料,并对Nd0.7Ce0.3MnO3薄膜材料的电脉冲诱导电阻可逆变化（EPIR）效应进行了研究。实验结果发现,Nd0．7Ce0.3MnO3结晶性很好且纯度高,没有出现CeO2的杂质相。EPIR效应测试表明：Nd0.7Ce0．3MnO3薄膜材料具有良好的EPIR效应,其高低电阻态之间的电阻值最大可以达到5～6个数量级的变化,有利于提高非挥发性存储的存储密度,同时材料的高低电阻态电阻具有良好的保持性。     

A位无序掺杂锰氧化物La2/3-xYxCa1/3-ySryMnO3的微结构和居里温度研究

采用固相反应法制备了A位无序掺杂锰氧化物La2/3-xYxCa1/3-ySryMnO3系列样品;利用Rigaku Dmax-rB 12 kW转靶X-ray衍射仪和振动样品磁强计Lakeshore7300对样品进行表征,并通过Rietveld方法对X-ray衍射谱进行结构精修。讨论了A位掺杂无序度σ2对样品的相、微结构（Mn—O键长、Mn—O—Mn键角等参数）和居里温度的影响。结果表明：随着掺杂浓度x和无序度σ2的增加,样品仍然保持单相性较好的钙钛矿正交结构,晶格常数a,b,c和晶胞体积V没有发生大的变化;Mn—O—Mn键角增加和Mn O键长减小;样品的居里温度下降,但x=0.20时,La2/3-xYxCa1/3-ySryMnO3居里点反而拉伸增大。     

溶胶-凝胶法制备聚氨酯/二氧化硅杂化材料

为了获取一种新型的聚氨酯／二氧化硅杂化材料，采用溶胶-凝胶法制备了不同二氧化硅含量的聚氨酯／二氧化硅杂化材料，详细研究了加水量、催化剂HCl用量、温度对溶胶-凝胶过程的影响以及偶联剂的加入对杂化材料性能的影响；确定了实验最佳条件为：n(H2O)：n(TEOS)=4：1，n(HCl)：n(TEOS)=0．5：1，通过红外光谱、扫描电镜和光电子能谱等手段考察了杂化材料的结构与性能。结果表明：通过溶胶-凝胶法制备的PU／SiO2杂化材料中PU和SiO2形成了较强的化学作用，而不是简单的共混，同时随着SiO2含量的增加材料的脆性逐渐增大，但加入偶联剂后，材料的韧性又有所提高。     

Sr离子含量的减少对于La0.60Sr0.25Na0.15MnO3材料性能的影响

利用溶胶-凝胶法（sol-gel）制备了稀土锰氧化物多晶样品La0.60Sr0.25-xNa0.15MnO3,发现随着Sr离子含量的减少,样品在室温附近庞磁电阻效应有了明显的改善。在1.8 T的磁场下,对于x=0.05的样品,其CMR值在240~320 K的温区范围内均保持在5.3%（±0.2%）,温度稳定性有显著改善。