Gd掺杂对Bi2Sr2Ca1—xGdxCu2Oy单晶载流子浓度和各向异性电阻率？…

系统地研究了Ｇｄ掺杂对Ｂｉ２Ｓｒ２Ｃａ１－ｘＧｄｘＣｕ２Ｏｙ单晶超导电性及各向异性电阻率的影响。Ｔｃ满足Ｔｃ／Ｔｃ,ｍａｘ＝１－８２．６（ａｘ＋ｂ）＾２,并随Ｇｄ含量的增加而下降,这是由于Ｇｄ掺杂引起载流子浓度减小所导致。在ｘ≥０．１９时,ρａｂ（Ｔ）在Ｔｃ随近有类半导体行为,ｄρａｂ／ｄＴ随Ｇｄ含量的增大而增大。ρｃ（Ｔ）呈半导体行为,并可用唯象公式ρｃ（Ｔ）＝（ａ／Ｔ）ｅｘｐ（△／Ｔ）＋ｂＴ＋     

Bi-2212单晶各向异性电阻率的研究

测量了从欠掺杂区域到过掺杂区域变化的一系列Ｂｉ２２１２单晶样品ａｂ平面内和ｃ方向电阻率ρａｂ．ρｃ随温度Ｔ的变化关系．按照几种不同模型分析了测量数据．比较两块处于过掺杂区域的Ｂｉ２Ｓｒ２ＣａＣｕ２Ｏ８＋δ（单晶和Ｂｉ２－ｘＰｂｘＳｒ２ＣａＣｕ２Ｏ８＋δ（单晶，发现尽管平面内电阻率ρａｂ与温度Ｔ依赖行为类似，且Ｔｃ值基本相同，但ｃ方向电阻率ρｃ与温度Ｔ的行为差别很大．这种氧空缺和离子取代的无序效应所造成ｃ方向电阻率ρｃ不同温度行为表明：无序的阻挡层（ｂｌｏｃｋｉｎｇｌａｙｅｒ）对于ｃ方向电阻率ρｃ有重要影响     

Bi_2Sr_（1．8）La_（0．2）Cu_（1－x）MxOy（M＝Ni，Z

本文利用Ｘ射线衍射、电子衍射和拉曼散射对Ｂｉ２Ｓｒ１．８Ｌａ０．２ＣＵ１－ｘＭｘＯｙ（Ｍ＝Ｎｉ，Ｚｎ）体系的微结构进行了研究．实验表明，随着掺杂量的增加，掺Ｚｎ体系的结构畸变明显大于掺Ｎｉ体系的结构畸变．由此看来，非磁性杂质Ｚｎ之所以比磁性杂质Ｎｉ对Ｔｃ具有更大的抑制作用，应该归因于Ｚｎ掺杂造成材料中严重的结构畸变．     

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Ｂｉ２Ｓｒ２ＣａＣｕ２Ｏ８＋δ（Ｂｉ２２１２）样品的ＣｕＯ面内和ＣｕＯ面外的电阻率ρｃ（Ｔ）和ρａｂ（Ｔ）．发现ρｃ（Ｔ）和各向异性比（ρｃ（Ｔ）／ρａｂ（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，ρｃ随温度线性下降，而各向异性比与温度仅有微弱的依赖关系．ρｃ（Ｔ）和ρｃ（Ｔ）／ρａｂ（Ｔ）的值可以用Ａｌｅｘａｎｄｒｏｖ和Ｍｏｔ建立的双极化子模型很好地加以拟合     

R＿（1－x）Pr＿xBa＿2Cu＿3O＿（7－δ）超导T＿c平台的离子尺寸效应

系统地研究了Ｒ＿（１－ｘ）Ｐｒ＿ｘＢａ＿２Ｃｕ＿３Ｏ＿（７－δ）的超导Ｔ＿ｃ与Ｐｒ替代浓度ｘ的关系。发现在离子半径ｒ＿ｉ≤ｒ＿ｉ（Ｄｙ）时，在低Ｐｒ浓度范围内存在一个超导Ｔ＿ｃ平台，并且平台宽度表明一个Ｒ￣（３＋）离子尺寸效应。我们认为，Ｔ＿ｃ平台宽度的离子尺寸效应可能起源于Ｐｒ４ｆ电子局域态的改变。提出一个临界Ｒ￣（３＋）离子半径ｒ＿（ｉｃ），ｒ＿ｉ＞ｒ＿（ｉｃ）时ＲＢａ＿２Ｃｕ＿３Ｏ＿（７－δ）的超导电性消失     

Bi2Sr1.8La0.2Cu1—xMxOy（M=Ni,Zn）体系的微结构研究

本利用Ｘ射线衍射、电子衍射和拉曼散射对Ｂｉ２Ｓｒ１．８Ｌａ０．２Ｃｕ１－ｘＭｘＯｙ（Ｍ＝Ｎｉ，Ｚｎ）体系的微结构进行了研究。实验表明，随着掺杂量的增加，掺Ｚｎ体系的结构畸变明显大于掺Ｎｉ体系的结构畸变。由此看来，非磁性杂质Ｚｎ之所以比磁性杂质Ｎｉ对Ｔｃ具有更大的抑制作用，应该归因于Ｚｎ掺杂造成材料严重的结构畸变。     

掺Ba的Bi—sr—Cu—O的单晶Raman散射研究

利用Ｒａｍａｎ散射研究了Ｂｉ２Ｓｒ２－ｘＢａｘＣｕＯｙ（ｘ＝０，０．２，０．４）单晶样品的声子振动性质。实验结果表明，在Ｂｉ２Ｓｒ２－ｘＢａｘＣｕＯｙ体的Ｒａｍａｎ谱中主要出现以下几个频率的特征振动模，即１９６，３００，４６０，６２５和６６０ｃｍ＾－１；而频率为１９６，３００，６２５，６６０ｃｍ＾－１的特征峰的强度随着Ｂａ掺杂量的增加而增加。在早期的工作中，我们曾经研究过Ｂａ的掺杂对Ｂｉ２２０１相     

THE SUPERCONDUCTIVITY IN Al-DOPEDY_(1-x)Al_xBa_2Cu_3O_y

本文系统地分析了在Ｙ１－ｘＡｌｘＢａ２Ｃｕ３Ｏｙ（ｘ＝０～０．７）中用Ａｌ替代Ｙ的替代效应．我们发现当ｘ＜０．４时，Ａｌ主要替代在Ｙ位，引起结构畸变，从而导致氧含量的减少和Ｏ－Ｔ相变，转变温度随Ａｌ含量增加而下降．当掺杂量大于０．４，Ａｌ开始占据Ｃｕ（１）和Ｃｕ（２）位，样品变为四方结构，Ｔｃ迅速下降．ＸＰＳ分析表明，Ａｌ的位置依赖于掺杂量，随掺杂浓度的增加Ａｌ依次替代Ｙ，Ｃｕ（１），Ｃｕ（２）．同时我们观察到Ｔｃ和ＣｕＯ２平面间相互作用的正比关系．     

Bi—2212相欠掺杂区域的反常输运性质研究

测量了Ｂｉ２Ｓｒ２Ｃａ１－ｘＹｘＣｕ２Ｏ８单晶样品ａｂ平面内电阻率ρａｂ和多晶样品电阻率ρ．热电势Ｓ随温度Ｔ的变化关系（单晶：ｘ的范围从０到０．１５；多晶：ｘ的范围从０到０．４）．在单晶和多晶样品中，都系统地观察到类似于ＹＢａ２Ｃｕ４Ｏ８，ＹＢａ２Ｃｕ３Ｏ７－ｙ体系中由于自旋能隙出现而引起的输运性质反常现象．详细地讨论了上述实验结果，并与角分辨率光电子能谱实验（ＡＲＰＥＳ），电子拉曼实验结果进行比较，得出Ｂｉ２２１２相欠掺杂区域的电子相图．     

过量La掺杂的Bi—2201单晶的超导电性

在极度Ｌａ掺杂的Ｂｉ２Ｓｒ２－ｘＬａｘＣｕＯ６＋ｙ单晶中发现Ｔｃ高达３６Ｋ的超导相。Ｘ射线衍射（ＸＲＤ图和劳埃斑点实验都显示单晶具有很好的质量。ＥＤＸ分析结果和由ＸＲＤ得到的单晶ｃ轴长度均证实单晶处于极度Ｌａ掺杂的区域。一般来说，处于如此高Ｌａ掺杂区域的Ｂｉ－２２０１体系不表现出超导电性。因为我们的样品曾在Ｏ２中６８０℃退火１０小时，而且极度Ｌａ掺杂会导致长程反铁磁有序背景。所以我们将这种高Ｔｃ的     

Magnetic ordering in HoRu2Si2, HoRh2Si2, TbRh2Si2 and TbIr2Si2 by neutron diffraction

Neutron diffraction study of polycrystalline HoRu₂Si₂, HoRh₂Si₂, TbRh₂Si₂, and TbIr₂Si₂ was performed in the temperature range between 4.2 and 300 K. For HoRu₂Si₂ the magnetic spin alignment of a linear transverse wave mode below the Néel temperature 19 K is observed. This static moment wave is propagating along the b-axis with k=(0, 0.2, 0) and is polarized in the c-axis. The root-mean-square and maximum saturation moments per Ho atom are 9.26 and 13.09μ_B, respectively. HoRh₂Si₂, TbRh₂Si₂ an TbIr₂Si₂ are simple collinear antiferromagnets of +-+- type with Néel temperatures of (27±1), (98±2) and (72±3) K, respectively. For TbRh₂Si₂ and TbIr₂Si₂ magnetic moments are localized on RE ions only and are aligned along the tetragonal axis, while for HoRh₂Si₂ they form an angle ø = (28±3)°.     

μ+SR study of LaNi2As2, URh2Si2 and CeRh2Si2

Muon spin relaxation experiments have been carried out in the paramagnetic and magnetically ordered states of URh₂Si₂ and CeRh₂Si₂. As the magnetic structure of these compounds is well known, these measurements can help to characterise their magnetic properties probed by μSR and to understand the μSR results of the heavy fermion compounds of the same crystallographic family. Our measurements show that the muons occupy two different crystallographic sites. The spectra of URh₂Si₂ and CeRh₂Si₂ in the magnetically ordered states are very different, probably reflecting their different magnetic structures. The spectra obtained on CeRh₂Si₂ are similar to the published spectra of the heavy fermion compound CeCu_2.1 Si₂. Muon spin rotation measurements on LaNi₂As₂ indicate that the muon is diffusing at 150 K.     

13C-selective IRMPD of CBr2F2/Cl2 and CCl2F2/Br2 systems

The CO₂ TEA laser irradiation of CBr₂F₂ in the presence of Cl₂ yielded ¹³C-enriched CBrClF₂ and ¹³C-enriched CCl₂F₂ under selected experimental conditions. As the photolysis proceeded, the ¹³C concentration of CBrClF₂ decreased gradually and that of CCl₂F₂ increased up to 90% or higher. These results can be explained by the mechanism involving the secondary ¹³C-selective IRMPD of the primary product CBrClF₂. On the other hand, the carbon-containing product for a CCl₂F₂/Br₂ system was only CBrClF₂; the further IRMPD of which probably regenerated CBrClF₂ in the presence of Br₂. The decomposition probabilities of ¹²C- and ¹³C-containing molecules in both systems were measured as functions of laser line, laser fluence, and reactant pressures.     

Polar optic phonons in Hg2Cl2 and Hg2Br2

Far infrared (30–430 cm^?1) reflectivity measurements of Hg₂Cl₂ and Hg₂Br₂ single crystals have been performed in polarized light. The spectra, which are in agreement with group-theoretical predictions, were analyzed by the oscillator fitting procedure and Kramers-Kronig method. The results are compared with the existing data from other measurements and the large anisotropy of polar modes is briefly discussed. The polarization vectors of all long-wavelength symmetry modes were determined group-theoretically.     

Magnetostriction of SmMn2Ge2 and GdMn2Ge2 intermetallic compounds

Longitudinal and transverse magnetostrictions of polycrystalline samples of intermetallic compounds RMn₂Ge₂ (R=Sm or Gd) are measured in pulsed magnetic fields up to 250 kOe. It is found that linear magnetostrictive strains of about 10^?3 arise in a temperature range in which the magnetic field causes a change in the magnetic state of a manganese magnetic subsystem. The results obtained are described within the model of a two-sublattice ferrimagnet with a negative exchange interaction in the manganese subsystem in terms of a strong dependence of this interaction on interatomic distances.     

Superconductivity in LaPd_2Bi_2 with CaBe_2Ge_2-type structure

正Since the discovery of superconductivity in LaFeAsO_(1-x)F_x,the high-T_c iron-based superconductors have been extensively studied from both experimental and theoretical viewpoints [1-8]. However, the mechanism of the unconventional superconductivity is still to be resolved. To     

Structural,magnetic and neutron diffraction studies on TbFe2-TbAl2, TbCo2-TbAl2 and HoCo2-HoAl2

Both pseudobinary systems exhibit large homogeneous regions of cubic and hexagonal Laves phases. Ordering tendencies on crystallographic sites between Al and the transition metals are observed in the hexagonal type.Electron transfer to the transition metals quenches their moments so that they become nonmagnetic at high Al concentrations. The peculiarities in the mechanism of magnetization which appear in rare earth dialuminides when Al is replaced by a transition metal have been studied in detail at cryogenic temperatures.The first replacement of Al results in a decrease in saturation moment. Neutron diffraction verifies the low ordered rare earth sublattice moments and reveals the ‘lost part’ as a disordered component. Considerable magnetic hardness develops in certain regions of concentration often connected with spontaneous increases in magnetization with field. All available evidence suggests the presence of unusual domain wall effects to be responsible for this effect. High remanences develop in both the hexagonal and in the cubic structures in the intermediate region. The development of disordered magnetic components is connected either with the disorder on crystallographic sites or changes in the free electron concentration.