Ti掺杂对La0.67Ba0.33MnO3磁性和磁电阻影响

系统地研究了Ti掺杂对La0.67Ba0．33MnO3颗粒材料磁性、电性和磁电阻效应的影响，随着Ti含量的增加，材料的磁化强度和居里温度快速下降，电阻率急剧增大，电阻率的峰值逐渐向低温移动。Ti的掺杂对材料低温下低场磁电阻影响不大，主要是显著提高了材料的本征磁电阻。1％的Ti掺杂使材料的室温磁电阻得到显著增强，1T磁场下，室温磁电阻达到-8．4％，比未掺杂的La0.67Ba0．33MnO3材料增强了50％。     

La0.67Sr0.33MnO3中Ag-Ti的掺杂效应

将La0.67Sr0.33MnO3（LSMO）、Ag2O及TiO2粉混合经高温烧结后制备了钙钛矿相/xAg两相复合体系（x是Ag与钙钛矿材料的物质的量比）,系统地研究了Ag-Ti的共掺杂对LSMO电性和磁电阻效应的影响.0.07摩尔比Ti4＋离子的B位掺杂使LSMO的居里温度降至室温.Ag的掺入对Tc影响不大,Tp逐渐升高.由于钙钛矿颗粒属性的改善和金属导电通道的出现,材料的电阻率明显下降.Ag掺杂使室温磁电阻得到显著增强,室温下从x=0.30样品中得到最大的磁电阻,约为32%,是La0.67Sr0.33MnO3样品的8倍,La0.67Sr0.33Mn0.93Ti0.07O3样品的1.6倍.     

Nb5+的掺杂引起La0.67Sr0.33MnO3增强的磁电阻效应

将Nb2O5掺杂到用溶胶-凝胶法制备的La0.67Sr0.33MnO3(LSMO)微粉中,XRD测量结果表明所有样品均为单相菱面结构.随着Nb5 掺杂量的增加,材料电阻率发生显著变化.在x=0.06的掺杂样品中得到最高为1110Ω·cm电阻率(x是掺入的Nb离子与母体材料的摩尔比),比LSMO高5个数量级,这是由于晶界处以及颗粒内部增加的自旋相关的散射和隧穿效应所致.Nb5 离子的掺杂使样品的低场磁电阻(LFMR)和高场磁电阻(HFMR)效应都有所增强.77K下,0.1和1T磁场下在x=0.07样品中分别得到25%和42%的磁电阻效应,分别是LSMO样品的2倍和1.7倍.室温下x=0.03样品的磁电阻最大,为7%.其中,LFMR来源于颗粒晶界处电子的自旋相关隧穿及散射作用,而HFMR来源于表面层的自旋非共线结构.     

La0.67Ba0.33MnO3中Cu掺杂对电特性和室温磁电阻的影响

在溶胶-凝胶法制备的La0.47Ba0.38MnO3(LBMO)微粉中掺入CuO粉,制成一系列(LBMO)／／(CuO),(x=0．01～0．1,为摩尔比)掺杂材料,实验结果发现．随着Cu掺杂量的增加,材料的磁化强度和居里温度变化不大,材料的电阻率先快速减小,而后缓慢增大,当x=0．01时在全温范围内电阻率都达到最小值,这与Cu离子的价态变化有关。实验还发现Cu离子的掺入可以使材料的室温磁电阻逐步提高．当掺入10%的Cu时,室温磁电阻比达到-8．4％。比未掺杂的LBMO提高了50％。低电阻率导电陶瓷材料和大的室温磁电阻效应都是应用研究所关注的课题。     

La0.67Ba0.33MnO3中Ag的掺杂效应

在溶胶-凝胶法制备的La0.67 Ba0.33 MnO3(LBMO)微粉中掺入Ag2O粉,制成一系列(LBMO)／(Ag2O)x／2(x=0～0．35,为摩尔比)掺杂材料,实验结果发现Ag掺杂可明显降低材料的电阻率。当掺Ag量为x=0．25时,样品的电阻率达到最低值。同时在居里点附近,样品的峰值磁电阻得到显著增强。微量的Ag掺杂有助于提高样品的自旋相关隧穿磁电阻,使低场磁电阻得到显著增强。     

Nb5+的掺杂对La0.67Sr0.33MnO3磁性和传输性的影响

将用溶胶-凝胶法制备的La0.67Sr0.33MnO3(LSMO)微粉与(Nb2O5)x/2粉在1100℃下混合烧结,形成了具有钙钛矿结构的锰氧化物与LaNbO4的复合体系,x是掺入的Nb5 离子与母体材料的摩尔比.在x=0.07的样品中得到最大电阻率为23.74 Ω·cm,比LSMO 高三个数量级.Nb5 离子的掺杂使样品的低场磁电阻(LFMR)和高场磁电阻(HFMR)效应都有所增强.77 K下,0.1 T和1 T磁场下在x=0.07 样品中分别得到24 % 和33.8 %的磁电阻效应,是LSMO样品的2倍和1.7倍.室温下x=0.05样品的磁电阻最大,为9 %.其中,LFMR来源于颗粒晶界处电子的自旋相关隧穿及散射作用,而HFMR来源于表面层的自旋非共线结构.     

(1-x)La2/3Ca 1/3 MnO 3/xSb2O 5复合体系的电子输运和磁电阻行为

用两步法制备了（1-x）La2／3Ca1／3MnO3／xSb2O5复合样品．零场下电阻温度关系测量表明，对x〈3％范围。随Sb2O5含量增加，复合样品电阻率增大，绝缘体一金属转变温度降低；而对x〉3％范围，随Sb2O5含量增加。复合样品电阻率减小，绝缘体一金属转变温度提高．磁电阻测量表明，少量Sb2O5同La,2／3C＆1／3MnO3复合，可明显增强磁电阻效应．     

铋掺杂对SrTiO3薄膜微观结构及阻变行为的影响

采用溶胶-凝胶及快速退火工艺在p+-Si上制备了Bi掺杂SrTiO_3薄膜,构建了Ag/Sr_(1-x)Bi_xTiO_3/p+-Si结构阻变器件,研究了Bi掺杂量对薄膜微观结构、器件阻变行为及特性的影响。结果表明:Bi掺杂量较低时并未改变Sr_(1-x)Bi_xTiO_3薄膜的相结构,但随着掺杂比例的增大,晶粒尺寸也明显增大,当掺杂量x=0.16时,有Bi4SrTi4O15及TiO2相形成;不同Bi掺杂量的Ag/Sr_(1-x)Bi_xTiO_3/p+-Si器件均呈现出双极性阻变特性,且有明显的多级阻变行为。随Bi掺杂量的增加,器件的阻变性能逐步提高,当x=0.12时器件的高、低阻态电阻比值最大,达到105左右,并且在2 000次可逆循环测试下,高、低阻态电阻比未出现衰减,表现出良好的抗疲劳特性,但当掺杂量x达到或超过0.16后,器件的性能呈下降趋势。Bi掺杂量的增大会导致器件高阻态时的导电机制从空间电荷效应(SCLC)导电机制(x0.16)转变为肖特基势垒发射(x=0.16)。器件在低阻态下均遵循欧姆导电机制。     

Y2O3掺杂量对ZnO-Bi2O3-Nb2O5压敏陶瓷电性能的影响

通过掺杂Y2O3和优化烧结工艺制备了ZnO-Bi2O3-Nb2O5压敏陶瓷。利用XRD、SEM和VSR研究了Y2O3掺杂量对其电性能的影响。结果表明，随着Y2O3掺杂量增加，陶瓷电阻率ρ减小，非线性系数α增大；Bi2O3气氛下烧结（1170℃、保温2．5h）的陶瓷，当x（Bi2O3）和x（Nb2O5）为3％、y（Y2O...     

层状结构锰氧化物La2-2xSr1+2xMn2O7的EXAFS研究

采用溶胶—凝胶法和传统的固相反应法相结合,制备了双层钙钛矿结构锰氧化物La2-2xSr1 2xMn2O7较宽掺杂范围内(0．2≤x≤0．6)系列单相样品,并测量了各样品的X射线衍射谱(XRD)和扩展X射线吸收精细结构(EXAFS)谱。通过对XRD的分析证实样品均为Sr3Ti2O7型四方结构,空间群为I4／mmm,同时发现晶格参数a随掺杂量x的变化几乎不变,而c随x的增加则明显减小。通过对EXAFS的分析和研究得到MnO6八面体中c轴方向的Mn—O键长和Jahn—Teller畸变量△JT随掺杂浓度x的变化,发现在最佳掺杂浓度x=0．33附近,J-T畸变最大,显示出La2-2xSr1 2xMn2O7(0．2≤x≤0．6)系列锰氧化物的磁电性能与畸变量△JT密切相关。     

La0.67Sr0.33Co1-xFexO3体系的输运行为

研究了Co位Fe掺杂对La0．67Sr0．33Col—xFexo3体系的电输运性质和超大磁阻效应的影响．实验结果表明：在低掺杂(x≤0．1)时电阻率表现出金属性输运行为，在高掺杂(x＝0．2和0．3)时则为半导体行为．Fe掺杂削弱了Te处的MR峰值，但增加了低温下(T《Te)的MR值．La0．67Sr0．33Col—xFe2o3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。     

Dy和Yb部分替代La0.67Ca0.33MnO3中的La的影响

用Dy和Yb部分替代La0.67Ca0.33MnO3中的La使材料的居里温度单调下降，掺Dy使材料的相变温度单调下降，峰值电阻率迅速增大，磁电阻比急剧增大，掺入13％（原子分数）的Dy可使材料的最大磁电阻比增大近40倍，而掺Yb对磁电阻的影响要小得多，用自旋团簇理论可以解释庞磁电阻的形成。     

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.     

Research on a New Process of Preparation for Nano-SiO2 with High Activity and Mesopores

Nano-SiO_2 with high activity and mesopores was prepared through sol-gel synthesis followed by low-temperatureheat treatment and ball milling firstly in our experiments. TEM was performed to measure particle sizes. Nitrogenadsorption experiments were carried out to estimate specific surface area, porous distribution and porous ratio by BETand BJH methods. The content of Si-OH in SiO_2 surface was calculated by analysis of the results of hydrogen-oxygencontent mensuration (HOCM). As a result, appropriate heat treatment system and ball milling time are important topreparation for nano-SiO_2 with high activity and mesopores, which are 5～50 nm particles, 5～6 nm average aperture,85%～93% porous ratio, and 51%～55% Si-OH content in surface. Nano-SiO_2 with that structure has high surfaceenergy and activity. This process, which has simple facilities and operation rules, is a new way of preparation fornano-SiO_2 with high activity and mesopores.     

The Tb Doping Effect on the Room Temperature Magnetoresistance in (La1-xTbx)0.67Sr0.33MnO3 (x≤ 0.4)

by Tb in (La1-xTbx)0.67Sr0.33MnO3, the room temperature magnetoresistance △R/R0 drops at first, then undergoes an increase near x≈0.1, and finally drops again. The value of room temperature magnetoresistance at a field H=12 kOe for (La1-xTbx)0.67Sr0.33MnO3 is -3.56%. The enhancement of the room temperature magnetoresistance induced by an appropriate Tb substitution in (La1-xTbx)0.67Sr0.33MnO3 is correlated with the shifts of the Curie temperature and metal-insulator temperature to near room temperature. The drop of the room temperature magnetoresistance at large Tb doping-contents may be due to its lower TC and TMI far from the room temperature.     

Piezoresistivity in films of nanocrystalline manganites

Rare earth manganites having perovskite structure are susceptible to lattice strain. So far most investigations have been done with hydrostatic pressure or biaxial strain. We have observed that hole doped rare-earth manganites, which are known to display colossal magnetoresistance (CMR) also show change in its resistance under the influence of uniaxial strain. We report the direct measurement of piezoresistive response of La0.67Ca0.33MnO3 (LCMO) and La0.67Sr0.33MnO3 (LSMO) of this manganite family. The measurements were carried out on nanostructured polycrystalline films of LCMO and LSMO grown on oxidized Si(100) substrates. The piezoresistance was measured by bending the Si cantilevers (on which the film is grown) in flexural mode both with compressive and tensile strain. At room temperature the gauge factor approximately 10-20 and it increases to a large value near metal-insulator transition temperature (Tp) where the resistivity shows a peak.     

La0.67Ca0.33-0.5xLixMnO3多晶陶瓷结构及电学性能研究

用溶胶-凝胶法制备La0.57Ca0.33-0.5xLixMnO3(x=0.00,0.05,0.10,0.20)多晶陶瓷,用XRD分析多晶陶瓷的晶体结构,用SEM对多晶陶瓷的微观形貌进行分析,用标准四探针法测量电阻率-温度关系.结果表明,随着Li掺杂量的增加,所有样品均为斜方晶系,晶胞体积不断减小,金属-绝缘体转变温度(Yp)降低,电阻率不断增加,电阻率温度系数(TCR)不断减小.低温区域(T＜TP)的电阻率数据可以用ρ(T)=ρ0+ρ2T2 +ρ4.5T4.5进行拟合;高温区域(T＞TP)的电阻率数据可以用小极化子跃迁(SPH)模型和变程跳跃(VRH)模型进行拟合.整个温度区域(100～300 K)可以使用渗透模型对电阻率进行拟合.从拟合数据可知极化子激活能Ea随Li掺杂量的增加而增大,这是由于Li的加入减小了Mn3+-O2--Mn4+的键角,增大了有效带宽的间隙,因此也减弱了双交换作用,增大了电阻率.     

Lattice Effects and Irreversible Magnetoresistance in Gd Doped La—Ca—Mn—O

The Gd substituting effects for La in La0.67Ca0.33MnO3 has been studied .With increasing the substituting amount of Gd,the phase transition temperature of metal-isolator for the samples decreases,the corresponding peak resistivity increases,the Curie temperature decreases monotonically.The substitution of La-Ca-Mn-O with 11% Gd for La improved the magnetoresistance ratio by an order of magnitude.The effects of substituting Gd can be explained in terms of the lattice effects.An irreversible MR behaviour was observed in Gd-substituting compounds.This effect became marked when the substituting amount of Gd was greater than 7%.A maximum irreversible increment of MR ratio as large as 91% was obtained when Gd substituting amount was 11%.     

Ag／La0.67Sr0.33MnO3/Pt异质结构的电阻开关特性

采用脉冲激光沉积技术在Pt／Ti／SiO2／Si（100）衬底上制备出多晶La0.67Sr0.33MnO3（LSMO）薄膜,对其电脉冲致非挥发可逆电阻开关特性进行研究．结果表明,Ag/LSMO／Pt结构具有明显的室温电脉冲诱发电阻开关特性,且在宽电压脉冲作用下表现出较低的开关电压和较快的变阻饱和速度．由此可见,总脉冲能量或电荷（电流作用）为该结构的电阻开关效应提供驱动力．对Ag／LsMO／Pt结构进行了耐久性测试,表明该结构具有良好的疲劳特性与保持特性,可应用于新型不挥发存储器、传感器及可变电阻等电子元器件的研制