Bi2Sr2CaCu2O8单晶中的反常尖锋效应

使用牛津震动样品磁强计(VSM)研究了Bi₂Sr₂CaCu₂O₈单晶的磁滞回线.在20到40K温度之间发现了反常的尖锋效应,随样品O含量的增加,发生尖锋效应的外场也相应提高.可以认为在尖峰效应处发生了由涡漩物质的有序固态到无序固态的相变,在有少量点缺陷存在的BSCCO单晶相图上,B_sp线终止于20K温度处,在20K以下温区没有发生准格子到涡漩玻璃的相变,涡漩固相始终以准格子形式存在;可以认为尖峰效 关键词： 2Sr₂CaCu₂O₈单晶')" href="#">Bi₂Sr₂CaCu₂O₈单晶 磁滞回线 尖锋效应 相变     

Bi2Sr2CaCu2O8的晶体结构与超导性能

本文研究了Bi-Sr-Ca-Cu-O体系中理想成份为Bi₂Sr₂CaCu₂O₈化合物的超导性能和晶体结构。名义成份为BiSrCaCu₂O_5.5零电阻超导转变温度T_c(0)=81.5K。用X射线粉末衍射方法测定了Bi₂Sr₂CaCu₂O₈的晶体结构,其基本结构属体心四方晶系,空间群为D_4h¹⁷-l4/mmm,点阵常数a=3.825?,c=30.82?。每单胞化合式单位为2.2Ca占据2(a)等效点系,4Sr,4Bi和4Cu占据三组4(e)位置,其原子参数z分别为0.110,0.302和0.445,16O分别占据8(g),z=0.445和二组4(e),z=0.210和0.380。Bi₂Sr₂CaCu₂O₈晶体结构可认为是阳离子沿z轴的(00z)和((1/2)(1/2)z)交错排列,由Aurivillius相导生出来的。讨论了在Bi-Sr-Ca-Cu-O体系中可能存在的其它沿z轴不同堆垛层数的超导相。 关键词：     

在H2气氛中Bi2Sr2CaCu2O8+δ的热处理效应

对高品质单相多晶Bi₂Sr₂CaCu₂O_8+δ样品作真空或H₂气氛中不同温度下的热处理。由X射线结构分析,其正常态和超导态性质(特别是载流子浓度)的系统测量结果表明:Bi₂Sr₂CaCu₂0_8+δ样品在H₂气氛中热处理,其氧的释放可分为两个阶段:一是Bi-O层之间的过量氧原子的逸出,降低系统的载流子浓度,从而调节T_c;二是CuO₂面内氧原子的迁移,产生氧空位,使CuO₂面内Cu²⁺的短程二维反铁磁(2D-AFM)有序背景遭到破坏。可以认为:以往文献中报道的Bi₂Sr₂CaCu₂O_8+δ超导体的吸氢效应导致T_c的变化,很可能主要的并不是氢原子的电子掺杂行为,而是与吸氢过程中氧含量的变化相联系。 关键词：     

Bi2Sr2CaCu2O8超导单晶中的电阻反常行为

测量了Bi2 Sr2 CaCu2 O8单晶的ab面和c轴方向电阻 ,在其超导转变温度附近发现了反常的电阻峰出现 .其随外磁场 (>10 0Gs)和电流的增加而逐渐消失 .文章认为这个反常的电阻峰是由于单晶中超导相的不均匀分布而导致的准再进入行为 .     

不同氧含量Bi2Sr2CaCu2O８+δ单晶电阻率的各向异性

精确测量了在不同氧压下退火的单晶Bi₂Sr₂CaCu₂O_8+δ(Bi2212)样品的Cu-O面内和Cu-O面外的电阻率ρ_c(T)和ρ_ab(T).发现ρ_c(T)和各向异性比(ρ_c(T)/ρ_ab(T))随着载流子浓度增加而迅速下降.在过掺杂样品中,高于120K时,ρ_c随温度线性下降,而各向异性 关键词：     

Bi2Sr2CaCu2O8单晶a-b平面热电势率的各向异性

测量了Bi₂Sr₂CaCu₂O₈单晶a方向的热电势率S_a和b方向的热电势率S_b与温度T的关系,发现在a-b平面内热电势率存在各向异性。认为S_a与S_b的差异来源于b方向的调制结构,并用扩散热电势率S_d,声子曳引热电势率S_g和相关跳跃热电势率S_h三种贡献,对实验结果进行了 关键词：     

蓝宝石基片上制备大面积Tl2Ba2CaCu2O8超导薄膜

在2英寸双面蓝宝石基片上采用CeO₂作为缓冲层制备了高质量Tl₂Ba₂CaCu₂O₈(Tl-2212)超导薄膜.以金属铈作为溅射靶材,采用射频磁控反应溅射法生长了c轴织构的CeO₂缓冲薄膜,并研究了不同生长条件对于CeO₂缓冲层的晶体结构及表面形貌的影响.超导薄膜采用直流磁控溅射和后热处理的方法制备.扫描电子显微镜(SEM)图像显示,超     

YBa2Cu3O7-δ/LaAlO3和Tl2Ba2CaCu2O8/LaAlO3高温超导薄膜内的应变对其微波表面电阻影响的研究

YBa₂Cu₃O_7-δ/LaAlO₃ (YBCO/LAO) 超导薄膜是通过热蒸发沉积方法制备的,实验中使用的Tl₂Ba₂CaCu₂O₈/LaAlO₃ (TBCCO/LAO) 超导薄膜是通过直流磁控溅射方法制备的.通过分析两片超导薄膜的XRD谱计算出了两片超导薄膜内的应变,ΔC_{关键词： YBCO/LAO TBCCO/LAO 超导薄膜 应变 表面电阻}     

Bi2Sr2CaCu2O8+y掺Na样品的超导机制

用熔融法制备了Bi₂Sr₂CaCu₂O_8+y掺Ｎａ多晶样品，转变温度Ｔ_c提高到９０Ｋ以上，最大的零电阻温度达到９２．５Ｋ。在流动氧气退火后，未掺Ｎａ样品Ｔ_c显著降低，而掺Ｎａ样品Ｔ_c几乎不变，说明二者Ｔ_c提高具有不同的机制。据此我们认为Ｎａ替代了Ｂｉ而使Ｂｉｏ层电荷失去平衡，Ｃｕｏ面上电子转移到Ｂｉｏ层而形成空穴，空穴和电子的吸引相 关键词：     

NdBa2Cu3O7-δ/YBa2Cu3O7-δ多层膜体系的外延结构和磁通钉扎的研究

采用脉冲激光沉积技术,在单晶SrTiO₃基底上外延生长了一系列名义结构为p×(NdBa₂Cu₃O_7-δ(m)/YBa₂Cu₃O_7-δ(n))的多层膜和准多层膜(单元层NdBa₂Cu₃O_7-δ较厚而YBa₂Cu₃O_7-δ呈非连贯的岛状分布,m,n为激光脉冲数,p为重复周期).样品的超导转变温度在87—91 K范围,具体大小取决于不同的调制结构,多层膜的重复周期越大,层状界面越多,超导转变温度就越低.磁传输测量表明,准多层的样品不仅具有较高的超导转变温度,而且具有较强的磁通钉扎性能,77K零场下的临界电流密度高达4×10⁶ A/cm²,显示出良好的应用前景. 关键词： 2Cu₃O_7-δ')" href="#">NdBa₂Cu₃O_7-δ 多层膜 磁通钉扎 临界电流密度     

Sr2RuO4正常态的c方向的磁阻的研究

研究了典型的层状钙钛矿结构超导单晶Sr₂RuO₄在c方向的磁阻(Δρ/ρ₀)(H∥ab,J∥c)的变化.实验发现,磁阻表现出强烈的各向异性,并且随着温度T的降低,磁阻效应越明显;当在平面ab内旋转磁场H的方向时,磁阻成周期性变化;实验表明,磁场沿(110)方向时,出现磁阻的极大值.分别从Sr₂RuO₄的费米面的各向异性、载流子散射率、c方向能带色散的各向异性等方面来解释这些输运性质. 关键词： 2RuO₄')" href="#">Sr₂RuO₄ 磁阻     

ELECTROCHEMICAL OXIDATION OF La2CuO4 SINGLE CRYSTALS

Bulk superconducting La₂CuO_4+δ single crystals are obtained by using electrochemical intercalation technique from the as-grown insulating samples. Oxidation is carried out by constant current I=10μA at temperature T=70℃ and room temperature, respectively. Structure and magnetic properties are studied by low-temperature X-ray diffraction and susceptibility measurements. A superconducting phase with T_c of 19K and δ-0.12 can be attributed to the formation of oxygen clusters. Room temperature oxidation is inhomogeneous: two superconducting phases with T_c1 of 24K and T_c2 of 8K and an antiferromagnetic phase are coexisting in the crystal. It is found that the appearance of T_c in this system has the "step" tendency.     

Single crystal growth and characterizations of iron arsenide superconductor BaFe2-xNixAs2（0.0≤x≤0.12）

A series of big single crystals of BaFeFe_2-xNi_xAs₂ have been prepared by the FeAs self-flux method, with nominal nickel doping x = 0--0.12. The dimensions of the cleaved crystals are over 10~mm along ab plane and ～ 2~mm in maximum along the c direction. The measurements of x-ray diffraction, electrical resistance and magnetic property are carried out on the crystals. For the undoped parent compound BaFe₂As₂, both resistance and magnetization data display an anomaly associated with spin density wave and/or structural phase transition, with the transition temperatures at ～ 138~K. For Ni-doped BaFe_2-xNi_xAs₂ crystals, the superconducting critical temperature T_c ranges from 4.3~K for x=0.06 sample to 20~K for the optimally doped x=0.10 crystal.     

The microwave response of MgB2 /Al2O3 superconducting thin films

Microwave characteristics of MgB2/Al2O3 superconducting thin films were investigated by coplanar resonator technique. The thin films studied have different grain sizes resulting from different growth techniques. The experimental results can be described very well by a grain-size model which combines coplanar resonator theory and Josephson junction network model. It was found that the penetration depth and surface resistance of thin films with smaller grain sizes are larger than those of thin films with larger grain sizes.     

Magnetization anomaly and anisotropy of Bi2Sr2CaCu2−xNixO8 single crystals

We have observed the anomalous magnetization of Bi₂Sr₂CaCu_2−xNi_xO₈ (x = 0 and 0.02) single crystals. Anisotropy decreases with iodine intercalation although it expands the space between CuO₂ layers. Iodine intercalation seems to suppress the magnetization anomaly for Ni = 1% crystals, but not for Ni = 1% substituted crystals. We have discussed these results in terms of the increase of anisotropy by Ni substitution and the dimensional crossover of flux lines. Effects of both oxygen concentration and substitution of a magnetic element for the Cu site on the anisotropy of Bi₂Sr₂CaCu₂O₈ crystals show the same tendency as the case of the YBa₂Cu₃O₇ superconductor.     

Blue luminescence in Tm-doped KGd(WO4)2 single crystals

Up-conversion blue emissions of trivalent thulium ions in monoclinic KGd(WO₄)₂ single crystals at 454 and 479 nm are reported for a single pump laser source at 688 nm. We grew thulium-doped KGd(WO₄)₂ single crystals at several concentrations from 0.1% to 10%. We recorded a polarized optical absorption spectrum for the ³F₂+³F₃ energy levels of thulium at room temperature and low temperature (6 K). From the low temperature emission spectra we determined the splitting of the ³H₆ ground state. The blue emissions are characterized as a function of the dopant concentration and temperature from 10 K to room temperature. To our knowledge, this is the first time that sequential two-photon excitation process (STEP) generated blue emissions in thulium-doped single crystals with a single excitation wavelength.     

Vortex states in mesoscopic single crystals Bi2Sr2CaCu2O8+δ in high magnetic fields

The c-axis resistivity measurements were performed in the vicinity of the ab-plane in order to investigate the interaction between Josephson vortices and pancake vortices in Bi₂Sr₂CaCu₂O_8+δ mesoscopic single crystals. It was found that the angular dependence of the c-axis resistivity drastically changes in high magnetic field regime. The vortex lock-in transition becomes considerably broad in high magnetic fields, while the angular dependence of resistance exhibits the sharp lock-in features in low magnetic field region.     

取向Pr2Fe14B与Nd2Fe14B多晶磁化曲线的 计算

基于单离子晶场模型,提出了计算稀土-Fe(Co)金属间化合物取向多晶样品磁化曲线的方法.用此方法计算了取向Pr₂Fe₁₄B和Nd₂Fe₁₄ B多晶的高场磁化曲线,计算中使用了拟合化合物单晶磁化曲线得到的交换场与晶场参数.计 算曲线与实验曲线相符合. 关键词： 磁化曲线 晶场 2Fe₁₄B')" href="#">R₂Fe₁₄B