(La0.67Ca0.33MnO3)x/(ZrO2)1-x复合体系的磁性和传输特性

将用溶胶-凝胶法得到的La0.67Ca0.33MnO3(LCMO)微粉与ZrO2的颗粒进行复合,制备了(LCMO)x/(ZrO2)1-x渗流复合体系.当LCMO的体积分数为40%时,复合体系达到渗流阈值,此时材料在低温下的磁电阻得到显著增强.77 K时在10 mT的磁场下,(LCMO)0.4/(ZrO2)0.6的磁电阻比为7.8%,相对于LCMO增加了712%.低场磁电阻(LFMR)的增强是由于载流子在二者界面处发生的自旋相关隧穿效应.由于界面反应,不可避免地产生了Zr离子对Mn离子的B位替代,从而引起材料磁性M和居里温度Tc的下降.在x＜60%时,Tc保持在220 K附近基本不变,说明该B位替代是有限的.     

La_(0.67)Sr_(0.33)Fe_xMn_(1-x)O_3制备和奇特磁电阻效应

系列陶瓷氧化物La0.67Sr0.33FexMn1-xO3（0.055x0.33）通过共沉淀法工艺合成获得.经X射线衍射分析表明，所得氧化物均为单相，属三方结构.在零场和外加磁场下的四极法电阻测试结果表明：所有样品都具有较大的磁电阻效应，当x<0.13时，样品的电阻率-温度曲线中均出现电阻率峰（电阻率出现从半导体性向金属性的转变），该电阻率峰处的温度（Tp）随x的增大而向低温区移动，磁电阻效应是负值;x＝0.23时，样品已呈半导体性，磁电阻效应仍是负值;然而x＝0.33时，样品虽也表现为半导体性，但其中的磁电阻效应出现奇特的正负交替转换.     

Raman光谱研究La_(1-x)MnO_(3+δ)结构畸变对电输运性质的影响

采用固相反应法制备了La空位La_(1-x)MnO_(3+δ)(0.04,0.1,0.15,0.2)多晶样品,利用X射线衍射(XRD)与拉曼光谱(Raman)技术相结合研究了微观晶体结构对电输运性质的调控。X射线衍射结果表明,所有样品都具有菱方结构,空间群为R3C。Raman光谱研究表明每种样品在490和620 cm~(-1)都观察到比较明显的声子振动峰,分别对应MnO_6八面体的反对称伸缩振动模式和对称振动模式。随着La空位的增加和温度的降低,反对称振动模式峰均出现硬化现象,表明晶格轨道-自旋-声子(OSP)耦合作用的增强及Jahn-Teller畸变加剧。电输运性质研究发现,随着La空位浓度的增加,金属绝缘体转变温度降低,磁电阻效应减小。研究结果表明La空位导致OSP耦合作用增强,Jahn-Teller畸变加剧,致使La_(1-x)MnO_(3+δ)导电性变差。     

IrO_2掺杂对La_(0.7)Ca_(0.2)Sr_(0.1)MnO_3室温磁电阻效应的增强

将IrO2掺杂到固相反应法制备的La0.7Ca0.2Sr0.1MnO3(LCSMO)微粉中,制备了(1-x)La0.7Ca0.2Sr0.1MnO3+xIrO2(LCSMO/IrO2)复合体系。通过X射线衍射(XRD)、振动样品磁强计(VSM)以及直流四探针法测试,对复合材料的结构及性能进行了研究。结果发现,在复合体系中,一部分Ir4+离子取代了B位的Mn4+离子,另一部分以IrO2氧化物的形式存在于颗粒的边界处。随着IrO2掺杂量的增加,样品的比饱和磁化强度(σs)快速下降,而居里温度(TC)先下降后上升,电阻率也发生显著变化。与此同时,IrO2的掺杂使样品的低场磁电阻效应(LFMR)和高场磁电阻效应(HFMR)都有所增强,在H=3 kOe,T=307 K,x=5%的样品磁电阻达到11.65%;同样对于x=5%的样品,在H=2 T,T=295 K,磁电阻达到28%,室温磁电阻得到显著增强,这可能与本征磁电阻效应的特点及材料的TC和相变温度接近室温有关,另外掺杂物本身的特性对磁电阻的增强也有一定的影响。     

甲醇水蒸气重整制氢CuO/La_(1-x)Ce_xCrO_3催化剂

采用溶胶凝胶法制备了负载型CuO/La_(1-x)Ce_xCrO_3催化剂,研究了A位中Ce元素掺杂量对CuO/La_(1-x)Ce_xCrO_3催化剂结构、性质及其催化甲醇水蒸气重整制氢性能的影响。结果表明,掺杂Ce元素影响了CuO的还原性能和钙钛矿载体与CuO之间的作用力,进而影响了CuO/La_(1-x)Ce_xCrO_3催化剂对甲醇水蒸气重整制氢反应的催化性能。其中,CuO/La_(0.8)Ce_(0.2)CrO_3具有较好的催化性能,在280℃、水醇物质的量比为1.2、甲醇气体空速为800 h~(-1)的条件下,甲醇转化率达到100%。     

厚度效应对La0.67Ca0.33MnO3单晶薄膜电输运特性的影响

研究了外延La0.67Ca0.33MnO3（LcMO）／SrTiO3（100）和LCMO／NdGaO3（110）（NGO）薄膜的电输运特性随薄膜厚度的变化。尽管LCMO／STO和LCMO／NGO表现出不同的晶格畸变，但是，研究发现，在结构与输运特性之间没有直接的依赖关系，表现晶格应变效应对薄膜的电输运特性没有影响，如电阻率、金属-半导体转变、极化子激发能。     

La0.67Sr0.33Mn1-xCrxO3(0.00≤x≤0.30)的特殊输运行为

研究了La0.67Sr0.33Mn1-xCrxO3(0.00≤x≤0.30)体系的M-T曲线、ρ-T曲线和MR-T曲线. 实验结果表明 Cr对Mn位的替代对居里温度TC影响不明显, 但是随着Cr含量的增加, 电阻率和磁电阻出现双峰行为, CMR效应的温区被极大地拓宽了. 体系的特殊输运行为和异常CMR效应可能是Mn3+-O-Mn4+和Mn3+-O-Cr3+两种通道共存和竞争的结果.     

静电纺丝法制备La_(0.67)Ba_(0.33)MnO_3微纳米纤维及其红外发射率研究（英文）

采用静电纺丝法结合溶胶-凝胶技术制备了钙钛矿型La_(0.67)Ba_(0.33)MnO_3微纳米纤维,并利用差示扫描量热-热失重分析(DSC-TGA)、X射线衍射(XRD)、傅里叶变换红外光谱(FTIR)和扫描电子显微镜(SEM)等技术对产物进行了表征,利用IR-2红外发射率测试仪测试了La_(0.67)Ba_(0.33)MnO_3在280~370 K范围内的红外发射率.结果表明,La_(0.67)Ba_(0.33)MnO_3在600℃时已形成钙钛矿结构.随着煅烧温度的升高,La_(0.67)Ba_(0.33)MnO_3的形貌由纤维状向三维网络状转变,并最终失去纤维形态.在280~370 K范围内,La_(0.67)Ba_(0.33)MnO_3微纳米纤维的红外发射率随温度升高而升高,由0.564增加至0.689.利用钙钛矿材料双交换理论解释了这一现象,并进一步探讨了其在红外发射率可变材料中的应用前景.     

稀土空位庞磁电阻材料La(1-x)2/3Ca1/3MnO3的结构变化和输运性质

利用标准的固相反应法制备了La（1-x）2/3Ca（1/3）MnO3（x〈0.1）系列具有稀土La空位的庞磁电阻锰氧化物多晶样品.X射线粉末衍射（XRD）测量分析表明所有的样品均为单相,单胞具有正交对称性（Pnma）.分析了不同浓度的La空位对磁电输运性质的影响： 随着空位浓度的增大,绝缘体-金属的转变温度（TMI）几乎不变（约为267 K）,这表明少量的稀土空位不会破坏双交换作用;但当La空位浓度x〉0.04时,零场电阻率增大,但磁电阻（MR）值减小;在x=0.04时MR值在转变温度TMI处达到最大值约为220%（8 T）.     

择优掺杂的La-Ca-Na-Mn-O体系的庞磁电阻效应

利用溶胶-凝胶法制备出择优掺杂的名义组分为La_(1-x)(Ca_(1-y)Na_y)_xMnO_3(LCNM)的多晶样品.xRD测试表明样品均为钙钛矿结构.电输运测试表明所有样品均发生金属-绝缘体转变和顺磁一铁磁转变(转变温度分别用T_m和T_c表示),转变温度随Na含量的增加而增加,但是由于Ca,Na离子间价态的不同引起的磁不均匀性,同时含Ca和Na的样品电输运曲线在T_m温度以下出现肩型鼓包,同时表现出增宽的顺磁·铁磁转变过程,磁电阻测量发现所有样品均表现出庞磁电阻(CMR)效应,但是由于磁不均匀性,y约为0.25的样品表现出两个CMR峰.     

La0.67Ca0.33Mn1-xAlxO3体系的结构和输运特性研究

研究了Al离子的Mn位替代对巨磁阻材料La0.67Ca0.33MnO3体系的结构和输运特性的影响。结果表明,随Al3 替代量的增加,在整个替代范围内,晶胞体积表现出单调减小的规律。体系的电阻率急剧增加,绝缘体 金属转变温度TIM向低温方向移动,且与Al3 替代量存在线性关联。对少量Al3 替代量,在T>TIM的高温区域体系的输运特性满足热激活模型,在T相似文献   

Phase Separation and Transport Behavior in La0. 67-x Smx Sr0.33 MnO3 System

The magnetic behavior and the transport behavior of La0.67-x Smx Sr0.33 MnO3 （x = 0. 00, 0. 10, 0. 20, 0. 30, 0. 40, 0. 50 and 0. 60 ） systems were studied through measuring the M-T curves, electron spin resonance （ ESR ） curves and ρ-T curves. The samples exhibit a long-range ferromagnetic order when x = 0. 00, 0. 10, a cluster-spin glass state when x = 0. 20 and 0. 30, and an anti-ferromagnetic state at low temperatures when x = 0. 40, 0. 50 and 0. 60. The samples of x = 0. 30 and 0.40 show phase separation at temperatures above Te. The transport behavior of the sample of x = 0. 60 becomes abnormal when the doping is high, and an insulator-metal transition occurs near To and then a metal-insulator transition occurs, which rarely appears in an ABO3 structure. It is concluded that the magnetic and electric behavior changes of the systems depend on the extra magnetism and lattice distortion effect induced by Sm doping.     

Ca2+xLa8-x(SiO4)6O2-0.5x的合成及其导电机理

Ca2+xLa8-x(SiO4)6O2-0.5x的合成及其导电机理;溶胶凝胶法;硅酸盐氧基磷灰石;空位导电机理;电化学阻抗谱     

Gd掺杂对La0.67 Sr0.33 CoO3、La0.67 Sr0.33 MnO3体系磁行为的影响

M~T curves and M~H curves of the systems La0.67Sr0.33CoO3, La0.67Sr0.33MnO3 (x=0.00, 0.05, 0.10, 0.20, 0.30, 0.40, 0.50, 0.60, 0.67) were studied by experiments. Experimental results show that the magnetic structure of La0.67-xGdxSr0.33CoO3 system exhibits the cluster glass state with doping Gd increasing. The M~T curves of samples x>0.10 exhibit a peculiar phenomenon that M value rises sharply at low temperature range. The magnetic structure of La0.67-xGdxSr0.33MnO3 system changes from the long rang ferromagnetic order to the cluster glass state, and anti ferromagnetic state. The M~T curves of samples x≥0.50 decline sharply at low temperature range. The different phenomena shown by the two systems come from different coupling function between Gd and Co, Mn and from spin state transition of Co.     

K3[Tb(x)Eu(1-x)Ge3O8(OH)2] (x = 1, 0.88, 0.67, 0): 2D-layered lanthanide germanates with tunable photoluminescent properties

A family of novel 2D-layered lanthanide germanates K(3)[Tb(x)Eu(1-x)Ge(3)O(8)(OH)(2)] (x = 1, 0.88, 0.67, 0; denoted as TbGeO-JU-87, Tb(0.88)Eu(0.12)GeO-JU-87, Tb(0.67)Eu(0.33)GeO-JU-87, and EuGeO-JU-87) were synthesized under mild hydrothermal conditions in a concentrated gel system. They are isostructural, as confirmed by the powder X-ray diffraction analysis. The single-crystal X-ray diffraction analysis of EuGeO-JU-87 reveals that it is a 2D-layered [EuGe(3)O(8)(OH)(2)](n)(3n-) anionic framework, which is built up from GeO(4)H/GeO(4) tetrahedra and EuO(6) octahedra by sharing vertex O atoms. Charge neutrality is achieved by K(+) ions located in the free void space. Interestingly, photoluminescence studies show that Tb(0.88)Eu(0.12)GeO-JU-87 and Tb(0.67)Eu(0.33)GeO-JU-87 exhibit a high Tb(3+)-to-Eu(3+) energy-transfer efficiency and the Tb(x)Eu(1-x)GeO-JU-87 system displays tunable photoluminescent properties.     

Unusual physical and chemical properties of Cu in Ce(1-x)Cu(x)O(2) oxides

The structural and electronic properties of Ce(1-x)Cu(x)O(2) nano systems prepared by a reverse microemulsion method were characterized with synchrotron-based X-ray diffraction, X-ray absorption spectroscopy, Raman spectroscopy, and density functional calculations. The Cu atoms embedded in ceria had an oxidation state higher than those of the cations in Cu(2)O or CuO. The lattice of the Ce(1)(-x)Cu(x)O(2) systems still adopted a fluorite-type structure, but it was highly distorted with multiple cation-oxygen distances with respect to the single cation-oxygen bond distance seen in pure ceria. The doping of CeO(2) with copper introduced a large strain into the oxide lattice and favored the formation of O vacancies, leading to a Ce(1-x)Cu(x)O(2-y) stoichiometry for our materials. Cu approached the planar geometry characteristic of Cu(II) oxides, but with a strongly perturbed local order. The chemical activities of the Ce(1-x)Cu(x)O(2) nanoparticles were tested using the reactions with H(2) and O(2) as probes. During the reduction in hydrogen, an induction time was observed and became shorter after raising the reaction temperature. The fraction of copper that could be reduced in the Ce(1-x)Cu(x)O(2) oxides also depended strongly on the reaction temperature. A comparison with data for the reduction of pure copper oxides indicated that the copper embedded in ceria was much more difficult to reduce. The reduction of the Ce(1-x)Cu(x)O(2) nanoparticles was rather reversible, without the generation of a significant amount of CuO or Cu(2)O phases during reoxidation. This reversible process demonstrates the unusual structural and chemical properties of the Cu-doped ceria materials.     

YBa2Cu4O8/La2/3Ca1/3MnO3/YBa2Cu4O8异质结中的超导转变温度

采用对靶溅射技术制备了YBa2Cu4O8/La2/3Ca1/3MnO3/YBa2Cu4O8（Y-124/LCMO/Y-124）异质结, 研究了超导转变温度（TC）随LCMO层厚度（dL）的振荡行为. 当dL＞dLCR时, TC-dL曲线表现出清晰的非单调行为, 而金属-绝缘体转变温度（TMI）仅当dL＞dLCR时才能观测到. Y-124/LCMO/Y-124系统中所存在的这种对中间层的依赖关系, 显示了铁磁和超导耦合间强烈的相互作用.