钙钛矿锰氧化物（La0.8Ln0.2）2/3Ca1/3MnO3（Ln=La，Ce，Pr，Nd，Sm，Eu）的低场电输运性能分析

用溶胶-凝胶法制备了系列掺杂（La0.8Ln0.2）2/3Ca1/3MnO3（Ln=La,Ce,Pr,Nd,Sm,Eu）纳米级晶体。对比在La被其它镧系元素部分替代后,引起的A位离子平均半径的改变和磁矩变化对电输运及磁阻性能的影响,实验分析表明,各个样品在同样大小磁场下的磁电阻存在较大的差别,样品的磁电阻随原子序数的增加而明显变大,由镧系收缩引起晶格畸变所产生的本征磁电阻占主导地位,随着外加磁场的增加,不同掺杂样品间的峰值电阻差异被弱化;各掺杂样品间的转变温度差与掺杂离子半径差和磁矩差密切相关,且离子半径的差异对转变温度的改变贡献更大。     

La2/3Sr1/3Mn1-xCuxO3的磁电阻研究

采用溶胶一凝胶(sol-gel)法制备了La2/3 Sr1/3Mn1-x CuxO3(x=0.00、0.05、0.10、0.20)的多晶样品.利用振动样品磁强计测量了样品在室温下的磁性能;利用X射线衍射确定了粉体的组成;利用扫描电子显微镜观察了颗粒的形貌.在1.8T磁场作用下,当x=0时,在370K,样品的磁电阻几乎成...     

层状钙钛矿La2KMn2O7和La3KMn3O10的制备及磁、电性质的研究

采用溶胶-凝胶法制备了La2KMn2O7和La3KMn3O10两种后状钙钛矿锰氧化物多晶样品，研究了乙酸(CH3COOH)超声处理后对La2KMn2O7和La3KMn3O10结构和磁性的影响。结果表明超声取代可以提高样品的结晶度，对样品的结构及磁性能也有较大影响。本文对上述现象的可能原因也进行了初步讨论，并讨论了样品的磁电阻效应。     

双掺杂稀土锰氧化物La2/3(Ca1/3Sr2/3)1/3MnO3薄膜的输运特性

采用射频磁控溅射法制备了Ca、Sr双掺杂La2/3(Ca1/3Sr2/3)1/3MnO3(LCSMO)薄膜。电阻率-温度特性表明,薄膜在387K时发生铁磁金属相-顺磁非导体相相变。同时测试了薄膜在180,230和280K温度下的伏安特性．表明所制备的薄膜具有自阻效应,并分析了产生该现象的原因。     

La0.7Ca0.3-xSrxMnO3薄膜的电输运特性研究

采用溶胶-凝胶法制备La_0.7Ca_0.3-xSr_xMnO₃(LCSMO)薄膜, 探讨掺杂对结构、磁性能与电输运特性的影响机制。从X射线衍射(XRD)结果来看, 所有薄膜均具有典型钙钛矿结构。LCSMO薄膜的居里温度(T_C)和金属绝缘体转变温度(T_MI)均随Sr掺杂浓度增加而单调增加。总体看来, 当x ≤0.05时, LCSMO薄膜磁阻率类似于窄带系LCMO 系材料, 在T_MI周围较宽的温度区间内存在相分离, 而相分离过程中多相共存的无序状态是该类材料庞磁阻效应的主要来源。对特定温度下的磁阻率随磁场的变化进行分析, 当温度低于T_MI时, 磁阻率随磁场变化出现双梯度, 低磁场时晶界隧穿效应起主导, 该部分效应对磁场特别敏感, 高磁场时磁阻率主要来源于磁场对自旋波动的压制; 当温度接近或高于T_MI时, 晶界隧穿效应逐渐消失, 磁阻率随磁场线性变化, 磁场对自旋波动的压制起主导作用。     

Zn掺杂SrTiO3光催化剂的制备及性能研究

采用溶胶-凝胶法制备了不同Zn含量掺杂的SrTiO_3光催化剂(Zn-SrTiO_3),通过X射线衍射(XRD)、扫描电子镜显微(SEM)和荧光光谱(PL)对其进行了表征,用亚甲基蓝(MB)光催化降解实验评价了其光催化活性。结果表明,SrTiO_3经Zn掺杂后仍然保持了钙钛矿结构,Zn~(2+)进入SrTiO_3晶格对Sr2+进行了替位掺杂,导致晶格畸变;热处理温度升高,样品发生热团聚;适量的Zn掺杂,能有效降低光生电子和空穴的复合几率,提高SrTiO_3的光催化活性;当掺杂量n(Zn)∶n(Sr)=1.5∶100,热处理温度900℃时制备的样品光催化活性达95.5%,明显优于同等条件下纯SrTiO_3活性58.5%,样品具有较高的光催化活性和良好的稳定性。     

La0.67Sr0.33-xCuxMnO3的室温磁电阻效应

采用溶胶一凝胶(sol-gel)法制备了名义组分为La0.67Sr0.33-XCuXMnO3(x=0～0.33)的多晶样品,发现用Cu替代少部分Sr后样品的室温磁电阻比替代前的明显增大.在1.8T磁场作用下,当x＝0.15时,磁电阻峰值为27.7%,峰值温度为306K,当温度低于306K时磁电阻值随温度的升高而增大,当温度高于306K时磁电阻值随温度的升高而减小;当x＝0.1时,在295K-310K温度之间磁电阻值达19%左右,受温度影响很小;因此在提高了室温磁电阻值的同时,又提高了磁电阻的温度稳定性.这对于该类磁电阻材料的应用具有很大意义.     

La、Fe共掺杂TiO_2/活性炭纤维的制备及其光催化性能

采用溶胶-凝胶法,以硝酸镧和钛酸丁酯为原料,选取活性炭纤维作为载体,制备了La、Fe共掺杂TiO2/ACF复合材料,通过紫外灯照射,对甲醛气体进行光催化降解,考察材料的光催化活性。结果表明,适宜的La、Fe掺杂量能够提高TiO2/活性炭纤维的光催化活性。当La的掺杂量为0.5%(摩尔分数),Fe的掺杂量为0.5%(摩尔分数),焙烧温度为350℃时,La、Fe共掺杂TiO2/ACF光催化性能最佳,反应2h甲醛降解率达到98.9%。     

稀土Dy掺杂对纳米TiO2相变及光催化性能的影响

采用溶胶-微波法制备了稀土元素Dy掺杂的纳米TiO_2复合粉体,采用XRD、拉曼、XPS等手段对样品进行了表征和分析,并以甲基橙的光催化降解为探针反应,探讨稀土Dy掺杂对纳米TiO_2的相变及光催化活性的影响。研究结果表明:稀土掺量为1.3%、经550℃煅烧后制备的样品光催化活性显著提高,对甲基橙的降解率为92%。与未掺杂纳米TiO_2相比,稀土Dy掺杂可以阻碍纳米TiO_2晶粒的生长,增大了比表面积;提高其热稳定性,抑制TiO_2锐钛矿相向金红石相转变;并使TiO_2产生晶格缺陷从而增加纳米TiO_2粉体表面羟基含量和表面氧空位,抑制了光生电子和空穴的复合,增强纳米TiO_2的光催化活性。     

新型溶胶-凝胶工艺制备La0.5Ca0.5MnO3薄膜及性能分析

鉴于以醇盐为原料溶胶-凝胶制备La0.5Ca0.5MnO3薄膜工艺中存在诸多苛刻因素,本文以无机盐为原料采用溶胶-凝胶工艺在SiO2/Si(100)衬底上制备了La0.5Ca0.5MnO3薄膜.并用XRD、SEM和TEM等分析手段对薄膜进行了表征,通过不同磁场下电阻-温度(R-T)曲线,研究了样品的磁电阻(CMR)效应...     

Low Field Magnetoristance and Inhomogenieties in La2/3Ca1/3MnO3 Films

La_2/3Ca_1/3MnO₃ films were prepared using a conventional paint-on method on alumina and monocrystalline TiSrO₃ substrates. A significant difference between the peak resistivity temperature T _p=178 K and the magnetic transition temperature T _c=240 K was found in contrast to single crystal samples. The behavior of the magnetoresistance with temperature also differs from that found in bulk samples. Although the films show significant granular morphology differences, their transport and magnetoresistive properties are very similar. Maximum magnetoresistance ratios of 16% and 10% at 0.3 T and 77 K were obtained for films deposited on alumina and TiSrO₃ substrates, respectively. Magnetization measurements above T _c show a nonlinear behavior, consistent with the presence of ferromagnetic inhomogeneities within the paramagnetic phase. These results suggest that, in addition to the importance of grain boundary scattering in determining the magnetoresistance at low fields, microscopic inhomogeneity plays a role in determining magnetotransport properties.     

庞磁电阻薄膜La0.7Ca0.3MnO3的制备和输运特性

用溶胶-凝胶法在LaAlO3衬底上制备了La0．7Ca0．3MnO3薄膜,研究了La0．7Ca0．3MnO3薄膜的结构和输运特性．结果表明：La0．7Ca0．3MnO3薄膜呈现畸变钙钛矿结构,具有好的外延性;在同一温度下,电阻在磁场作用下变小,在283K和88K分别出现了金属-绝缘体转变,产生了双极值现象,并且在双极值附近电阻变化最大;用连续激光作用薄膜时,同样出现了双极值现象,在同一温度下,电阻反而变大,在升温和降温过程中出现了明显的滞后行为．根据双交换和小极化子理论,这些现象与Mn离子的eg电子受激跃迁有关．     

(La2/3Ca1/3)(Mn(3-x)/3)Fex/3)O3体系磁电阻行为的研究

通过系统地测量（La_2/3Ca_1/3）（Mn_{（3-x）／3}Fe_x／3）O₃（x＝0、0.1、0．2、0．3的体系样品的电阻率-温度关系以及一定温度下磁电阻率与磁场的关系,发现随x的变化其磁电阻率峰和电阻率峰均发生位移,磁电阻率峰值增大,并伴生磁电阻率峰展宽效应．作者认为由于Fe的替代,引起体系中Mn³⁺／Mn⁴⁺比率及磁矩的变化,加之外场对磁有序结构的调制作用,从而影响了Mn³⁺－O^－Mn⁴⁺的双交换作用,最终导致磁电阻行为发生变化．     

La0.67Ca0.33MnO3/YBa2Cu4O8/La0.67Ca0.33MnO3三层膜的时间效应研究

报导了La0.67Ca0.33MnO3/YBa2Cu4O8/La0.67Ca0.33MnO3薄膜中超导特性的时间效应.样品在空气中存放11个月后,超导转变温度都降低,而且每个系列样品的临界厚度增加.对用La0.67Ca0.33MnO3作保护层的YBa2Cu4O8薄膜进行时间效应测量,结果表明当La0.67Ca0.33MnO3层的厚度大于40nm时可以防止水对YBa2Cu4O8薄膜的影响.     

用内耗技术研究La0.7Pb0.3MnO3巨磁电阻材料

用低频扭摆法在多功能内耗仪上测量了巨磁电阻材料La_0.7Pb_O.3MnO₃(LPMO)的温度内耗谱和弹性模量.结果表明,内耗峰位与测量频率无关,并且峰高与频率成反比,弹性模量在对应的内耗峰处有明显的转折,内耗峰表现为相变峰的特征.结合电阻和磁化率的测试,解释了内耗和电阻-温度曲线的双峰现象,高温内耗峰和高温电阻峰与居里温度有很好的对应,来源于顺磁半导体向铁磁金属的转变,低温内耗峰和磁化率的单调下降来源于铁磁相分离过程,而较大的低温电阻峰部分来源于相分离过程.     

Magnetic and Electrical Transport Properties of Er2O3-Doped La0.7Ca0.3MnO3 Composites

The (La_0.7Ca_0.3MnO₃)_1?x /(Er₂O₃) _x composites with x=0, 1, 2, 3, 4, 7, 9, 15, 17, and 20% were prepared by a solid state reaction process. The magnetic and electrical transport properties of the composites were investigated. The X-ray diffraction (XRD), scanning electronic microscopy (SEM), and the calculation of lattice parameters of La_0.7Ca_0.3MnO₃ (LCMO) indicated that there is no reaction between La_0.7Ca_0.3MnO₃ and Er₂O₃; especially, compared with pure LCMO, a new metal-insulator transition temperature (T _P2) was observed at a lower temperature in some composites with x=1,2,3,4, and 7%, which may result from the existence of a new phase related to Er₂O₃ dopant at grain boundaries or surfaces of LCMO grains. An enhancement of low field magnetoresistance (LFMR) is obtained at temperature below 130 K for the composites with higher Er₂O₃ content, but the intrinsic CMR at T _P1 decreased monotonously with increasing Er₂O₃ content. The increased LFMR results from the spin-dependent scattering and spin-polarized tunneling at the grain boundaries and the decreased intrinsic CMR due to the Double Exchange (DE) interaction between Mn³⁺ and Mn⁴⁺ ions.     

A位阳离子无序对La_(2/3)Ca_(1/3)MnO_3结构和输运性能的影响

利用固相反应法合成了(La1-xDyx)2/3Ca1/3MnO3(x=0、0.1、0.2)材料,研究阳离子无序对微结构和电输运性能的影响。Rietveld方法拟合XRD结果表明,随着Dy掺杂浓度的增加,晶胞参数和Mn-O键长键角发生了明显的变化,造成MnO6八面体畸变。电输运性能显示:样品电导率随Dy掺杂量的增加而减小,其导电机制符合半导体小极化子模型。Dy掺杂浓度的增加使得钙钛矿ABO3的A位阳离子无序度增加,影响了样品的微结构;A位无序效应增强了载流子的晶格散射,抑制了电导率。     

Lattice Effect on the Transport Properties in Double Doped La2/3(Ca1-xSrx)1/3MnO3 Films

1. IntroductionThe manganese oxides REMnO3 (RE=trivalent rareearth elements) have the perovskite type structure. Ifthe trivalent rare earth element is partially doped withthe divalent alkaline earth element A (A=Ca, Sr, Ba,Pb), the doped manganese oxides RE1-yAyMnO3 haveexhibited a colossal magnetoresistance (CMR) effect[1~6],where the ions at A position affect the energy band widthand the transport characters of the RE1-yAyMnO3 ma-terials. While the Mn3+/Mn4+ ratio is fixed at 2,th…     

PLZST陶瓷衬底上La0.7Sr0.3MnO3薄膜生长及其磁性能和电输运特性研究

采用磁控溅射法在PLZST陶瓷衬底上制备了不同厚度的LSMO薄膜, 并对其微结构、磁性能及电输运特性进行了研究。结果表明, LSMO薄膜具有单一钙钛矿结构, 晶粒均匀, 表面平整, 其中20 nm厚LSMO薄膜粗糙度仅为2.93 nm。在10~300 K温度范围内, LSMO薄膜均具有大的磁电阻效应, 20 nm厚的LSMO薄膜磁电阻温度稳定性优异。随着薄膜厚度的增加, 薄膜的居里温度、金属绝缘体转变温度、磁化强度和导电性能降低。这可能是由于Pb、Sn、Zr等离子扩散进入LSMO薄膜中, 导致MnO₆八面体畸变造成的。     

Effect of Short-Range Ferromagnetic Ordering on the Electrical Transport Properties of (La0.9Bi0.1)2/3Ca1/3MnO3 in the Magnetic Field up to 40 T

The temperature and magnetic field dependence of the resistance of polycrystalline sample (La_0.9Bi_0.1)_2/3Ca_1/3MnO₃ was investigated in pulsed high magnetic field up to 40 T over a wide temperature region. In order to describe the magnetotransport properties of the sample, an extended Mott hopping conduction model was employed. Instead of B _J (gμ _B J(T)B/k _B T) in the ferromagnetic (FM) state and $B_{J}^{2}(g\mu_{B}J(T)B/k_{B}T)$ in the paramagnetic (PM) state, the magnetic field dependence of the resistance could scale nicely with the Brillouin function B _J (gμ _B J(T)B/k _B T) in all the given temperatures (above and below the Curie temperature T _c ). The deduced value of the average spin moment J(T) increases with the increasing of the temperature and reaches the maximum value (～35) around T _c . The large value of J(T) indicate the presence of magnetic clusters in the sample which is induced by the short-range ferromagnetic ordering, however, compared to the un-doped compound La_2/3Ca_1/3MnO₃, the value of J(T) is much smaller, which might be ascribe to the location of the 6s² lone pair electrons of Bi³⁺ ions in the sample (La_0.9Bi_0.1)_2/3Ca_1/3MnO₃.