Single-Ion Kondo scaling of the coherent Fermi liquid regime in Ce(1-x)La(x)Ni2Ge2

Thermodynamic and transport properties of the La-diluted Kondo lattice CeNi(2)Ge(2) were studied in a wide temperature range. The Ce-rich alloys Ce(1-x)La(x)Ni(2)Ge(2) were found to exhibit distinct features of the coherent heavy Fermi liquid. At intermediate compositions (0.7≤x≤0.9), non-Fermi liquid properties have been observed, followed by the local Fermi liquid behavior in the dilute limit. The 4f-electron contribution to the specific heat was found to follow the predictions of the Kondo-impurity model in both the local as well as the coherent regimes, with the characteristic Kondo temperature decreasing rapidly from about 30 K for the parent compound CeNi(2)Ge(2) to about 1 K in the most dilute samples. The specific heat does not show any evidence for the emergence of a new characteristic energy scale related to the formation of the coherent Kondo lattice.     

Ca2YSbO6:Bi3+的发光性能

本文首次研究了Bi3+在具有单斜结构的复合氧化物Ca2YSbO6中的激发和荧光光谱。发现Ca2YSbO6对于Bi3+是一个很有效的基质,该磷光体在315nm激发下,Bi3+产生很强的宽带发射,峰值位于400nm。荧光强度随Bi3+化学组成的改变发生明显规律性的变化,当Bi3+浓度为0.04摩尔时发光尤为有效。该磷光体有可能成为黑光灯粉和合成维生素c光化反应的光源。     

Interplay between crystal field splitting and Kondo effect in CeNi(9)Ge(4-x)Si(x)

The pseudo-ternary solid solution CeNi(9)Ge(4-x)Si(x) (0?≤?x?≤?4) has been investigated by means of x-ray diffraction, magnetic susceptibility, specific heat, electrical resistivity, thermopower and inelastic neutron scattering studies. The isoelectronic substitution of germanium by silicon atoms causes a dramatic change of the relative strength of competing Kondo, RKKY and crystal field (CF) energy scales. The strongest effect is the continuous elevation of the Kondo temperature T(K) from approximately 3.5?K for CeNi(9)Ge(4) to about 70?K for CeNi(9)Si(4). This increase of the Kondo temperature is attended by a change of the CF level scheme of the Ce ions. The interplay of the different energy scales results in an incipient reduction of the ground state degeneracy from an effectively fourfold degenerate non-magnetic Kondo ground state with unusual non-Fermi-liquid features of CeNi(9)Ge(4) to a lower one, followed by an increase towards a sixfold, fully degenerate ground state multiplet in CeNi(9)Si(4) (T(K)?～?Δ(CF)).     

Mechanisms of the pancake vortex and vortex line movement in the high Tc superconductors Bi2Sr2CaCu2O8+δand La1.93Sr0.07CuO4+δ

In the strict sense, it is not very clear why with magnetic field increasing, the normal-superconductive (NS) transition becomes broad for Bi2Sr2CaCu2O8+δ(Bi2212) while the NS transitions are almost parallel for La1.93Sr0.07CuO4+δ(La214). In this paper, R-T relations are measured by the six-probe method. We propose a moving mechanism of the pancake vortex and vortex line for Bi2212. The theoretical curves fit the experiment data well.     

New universality class of quantum criticality in Ce- and Yb-based heavy fermions

A new universality class of quantum criticality emerging in itinerant electron systems with strong local electron correlations is discussed. The quantum criticality of a Ce- or Yb-valence transition gives us a unified explanation for unconventional criticality commonly observed in heavy fermion metals such as YbRh(2)Si(2), β-YbAlB(4), YbCu(5-x)Al(x), and CeIrIn(5). The key origin is due to the locality of the critical valence fluctuation mode emerging near the quantum critical end point of the first-order valence transition, which is caused by strong electron correlations for f electrons. The wider relevance of this new criticality and important future measurements to uncover its origin are also discussed.     

4f-electron localization in CexLa 1-xM In5 with M=Co, Rh, or Ir

de Haas-van Alphen measurements on Ce(x)La(1-x)MIn(5) yield contrasting types of behavior that depend on whether M=Co and Ir or M=Rh. A stronger x-dependent scattering in the case of M=Co and Ir is suggestive of a stronger relative coupling, J/W, of the conduction electrons to the 4f electrons, which would then account for the development of a heavy composite Fermi-liquid state as x-->1. The failure of a composite Fermi-liquid state to form for any x in the case of M= Rh is shown to be inconsistent with theoretical models that propose antiferromagnetism to result from spin-density-wave formation.     

Cu掺杂对Kondo绝缘体CeNiSn低温比热的影响

CeNiSn是一种很有趣的重费米子化合物,其基态为Kondo绝缘体.采用化学元素替代的方法研 究Cu掺杂对CeNiSn多晶样品低温比热的影响.在流动高纯氩气的保护下,用电弧炉制备了一 系列的多晶样品CeNi_1-xCu_xSn(x＝0,002,006,008).X射 线粉末衍射分析表明,制备出来的样品均为单相多晶.随着Cu掺杂量的增加,样品的晶格参 数增大.采用绝热热脉冲法测量样品的比热,结果表明随着Cu掺入量的增加,相应样品的低温比热也随之增大,能隙逐渐减小 关键词： 重费米子 Kondo绝缘体 CeNiSn 比热 反铁磁有序     

Spectroscopic observation of bipolaronic point defects in Ba(1-x)KxBiO3

An infrared-absorption band centered at 0.85 eV, which is below the big optical absorption at the charge-density-wave (CDW) gap energy of 1.85 eV, has been observed for semiconducting single crystalline Ba(1-x)KxBiO3. With substituting K for Ba, the spectral weight of the new band increases with x, while that of the CDW-gap excitation decreases. Since the impurity state with the K substitution is known to be nonmagnetic at low temperatures, Bi3+ the state with 6s2 electrons surrounded by the six Bi5+ ions forms a small bipolaron by losing a pair of electrons in the Rice-Sneddon model. The new band is assigned to a transition from the lower-Peierls band to a state of the bipolaronic point defect.     

Spatial distribution of the induced magnetization in CeNi

In order to confirm the electronic nature of the susceptibility measured on the Pauli paramagnet CeNi and more especially the origin of the maximum of the susceptibility observed at 140 K, a polarized neutron diffraction study has been performed at 20 and 140 K, in an applied field of 4.6 T, leading to induced magnetization density maps at these two temperatures. Whereas in the Pauli paramagnet CeNi₅, the induced magnetization is localized on the nickel sites only, in CeNi it is localized on the cerium site at both temperatures and no magnetic density appears on the nickel site. Thus, magnetism in CeNi arises from the 4f electrons of cerium which is in an intermediate valence state.     

Investigation of the phase diagram and superconductivity of Hg−Pb−Bi−Ba<Subscript>2</Subscript>CaCu<Subscript>2</Subscript>O<Subscript>6+δ</Subscript>

Compounds of the series Hg_(1?x?y) Bi_xPb_yBa₂CaCu₂O_6+δ (0≤x,y≤0.5) are synthesized directly from the metal oxides without using a precursor. Structural, and morphological investigations are made by x-ray diffraction, SEM and EDXA techniques. Bi and Pb substitution suppresses or enhances the simultaneous formation of Hg-1201 and Hg-1223 phase. Multiphase Hg_0.8Bi_0.2Ba₂CaCu₂O_6+δ has a maximum T_c of 134K. For Bi and Pb concentrations higher than 0.5 mole, non-superconducting phases are formed.     

Monte Carlo calculation using a personal computer for electron probe microanalysis

Monte Carlo simulation for calculating x‐ray spectra under electron impact is carried out by a personal computer. Reduction of the CPU time by reducing the number of incident electrons for calculation is performed. One of the methods used to reduce the number of incident electrons to obtain the results within an acceptable error is provided. We limit the present report to five typical compounds: an oxide (Al₂O₃), a nitride (TiN), a carbide (Al₄C₃), a light–light element compound (BN), and a heavy–light element compound (PbS). We calculate the relative x‐ray intensity generated from the five compounds listed above with the change of the number of the incident electrons. The calculated x‐ray intensity is then converted into the mass % by the ZAF method. Comparisons are made between the calculation and experiment for Al₄C₃ and PbS. It is found that the present Monte Carlo method is useful for investigating a relationship between the number of incident electrons and the acceptable error. The results of 150 incident electrons can be applied in practical analysis, and the calculation time is less than 2 min. Copyright © 2004 John Wiley & Sons, Ltd.     

Geant4模拟δ电子对单粒子翻转的影响

利用Geant4蒙特卡洛程序包, 基于RPP (Rectangular ParallelePiped Volume)模型构建SRAM器件单元的灵敏体积, 编写了重离子在器件材料中的输运程序和单粒子翻转截面计算方法, 得到了简化器件结构的单粒子翻转截面σ与线性能量转移LET的关系曲线, 计算得到的翻转LET阈值和饱和截面与实验结果基本一致。模拟获得了LET值为99.69 MeV/(cm-2·mg)的Bi离子及LET值为69 MeV/(cm-2·mg)的Bi离子和Xe离子在器件材料中产生的δ电子分布图像,讨论了δ电子分布对翻转截面的影响。 计算了灵敏体积中能量沉积与δ电子分布的关系,认为δ电子分布对单粒子效应的影响随着器件的特征尺寸减小将更加严重。In this paper, the sensitive volume of SRAMs was constructed based on RPP(Rectangular ParallelePiped Volume) model using the Monte-Carlo code Geant4. The interactions of heavy ion with materials and the SEU(Single Event Upset) cross section calculation method were presented in the program. The SEU cross section curves with the linear energy deposition ware obtained. The SEU threshold value and saturation cross section were consistent with the testing data with heavy ions beam. The δ electrons distribution were different in the device material, which were generated by Bi ion with LETs of 99.67 MeV/(cm2·mg) and Bi ion, Xe ion with LETs of 69 MeV/(cm-2·mg). These results indicate δ electrons distribution impacts on the SEU cross section. According to the relation of energy deposition in the sensitive volume, the δ electrons distribution have more and more important effect on the Single Event Effect with reducing the feature size of semiconductor devices.     

Bi4-xLax Ti3O12-SrBi4-y Lay Ti4O15共生结构铁电材料拉曼光谱研究

在常温下 ,对La掺杂共生结构铁电陶瓷Bi4 -xLaxTi3O1 2 _SrBi4 -yLayTi4 O1 5[BLT_SBLT(x y) ,x y =0 0 0 ,0 2 5 ,0 5 0 ,0 75 ,1 0 0 ,1 2 5 ,1 5 0 ]进行了拉曼光谱研究 .结果表明 ,在掺杂量低于 0 5 0时 ,La只取代类钙钛矿层中的Bi,当掺杂量高于 0 5 0后 ,部分La开始进入 (Bi2 O2 ) 2 层 .La取代 (Bi2 O2 ) 2 层中的部分Bi以后 ,(Bi2 O2 ) 2 层结构发生变化 ,原有的绝缘层和空间电荷库的作用减弱 ,导致材料剩余极化下降 .La掺杂量增至 1 5 0时 ,样品出现弛豫铁电性 ,这与 30cm- 1 以下模的软化相对应 ,说明La掺杂可引起材料的结构相变     

Bi3+掺杂对Sr2MgSi2O7∶Eu2+荧光粉的结构及发光性能的影响

采用溶胶-凝胶法在还原气氛下制备了Sr₂MgSi₂O₇∶Eu²⁺,xBi³⁺(x=0,0.02,0.04,0.06,0.08,0.1)荧光粉,并用XRD、TG-DTA及激发与发射谱仪对样品的结构及发光性能进行了表征。结果发现:单掺杂Bi³⁺的Sr₂MgSi₂O₇样品的发射光谱所用的材料的激发光谱为一主峰为286 nm的宽带谱,这是由于激发态时Bi³⁺的³P₁→¹S₀电子能级跃迁而造成的;单掺杂Eu²⁺的Sr₂MgSi₂O₇样品的发射光谱所用的材料的激发光谱为一主峰为358 nm的宽带谱,这是典型的Eu²⁺的4f⁶5d¹→4f⁷跃迁而引起的。当Bi³⁺离子掺杂到Sr₂MgSi₂O₇∶Eu²⁺样品的摩尔分数为0.04时,样品的发射强度是未掺杂Bi³⁺离子样品的1.9倍。     

Correlation between valence electronic structure and magnetic properties in RCo_5(R=rare earth) intermetallic compound

The magnetisms of RCo_5(R = rare earth) intermetallics are systematically studied with the empirical electron theory of solids and molecules(EET).The theoretical moments and Curie temperatures agree well with experimental ones.The calculated results show strong correlations between the valence electronic structure and the magnetic properties in RCo_5 intermetallic compounds.The moments of RCo_5 intermetallics originate mainly from the 3d electrons of Co atoms and 4f electrons of rare earth,and the s electrons also affect the magnetic moments by the hybridization of d and s electrons.It is found that moment of Co atom at 2c site is higher than that at 3g site due to the fact that the bonding effect between R and Co is associated with an electron transformation from 3d electrons into covalence electrons.In the heavy rare-earth-based RCo_5 intermetallics,the contribution to magnetic moment originates from the 3d and 4f electrons.The covalence electrons and lattice electrons also affect the Curie temperature,which is proportional to the average moment along the various bonds.     

Topological surface states in lead-based ternary telluride Pb(Bi(1-x)Sb(x))2Te4

We have performed angle-resolved photoemission spectroscopy on Pb(Bi(1-x)Sb(x))2Te4, which is a member of lead-based ternary tellurides and has been theoretically proposed as a candidate for a new class of three-dimensional topological insulators. In PbBi2Te4, we found a topological surface state with a hexagonally deformed Dirac-cone band dispersion, indicating that this material is a strong topological insulator with a single topological surface state at the Brillouin-zone center. Partial replacement of Bi with Sb causes a marked change in the Dirac carrier concentration, leading to the sign change of Dirac carriers from n type to p type. The Pb(Bi(1-x)Sb(x))2Te4 system with tunable Dirac carriers thus provides a new platform for investigating exotic topological phenomena.     

Anomalous momentum dependence of the quasiparticle scattering rate in overdoped Bi2Sr2CaCu2O8

The question of the anisotropy of the electron scattering in high temperature superconductors is investigated using high resolution angle-resolved photoemission data from Pb-doped Bi2Sr2CaCu2O8 (Bi2212) with suppressed superstructure. The scattering rate of low energy electrons along two bilayer-split pieces of the Fermi surface is measured (via the quasiparticle peak width), and no increase of scattering towards the antinode (pi,0) region is observed, contradicting the expectation from Q=(pi,pi) scattering. The results put a limit on the effects of Q=(pi,pi) scattering on the electronic structure of this overdoped superconductor with still very high T(c).     

密闭高温高压溶样ICP-MS测定24个国际地质标样中的Sb和Bi

研究了ICP-MS分析中Bi,Sb,Te和As产生的记忆效应,其记忆效应Bi>Sb>Te>As。在低浓度硝酸介质中(0.01%～1%),贮存样品的聚丙烯瓶和ICP-MS的进样管道会对Bi元素产生严重的吸附作用。0.1%氢氟酸的清洗效果优于6%的硝酸,而6%的硝酸的清洗效果要优于0.1%高氯酸。在给定的仪器操作条件下,Sb和Bi的检出限分别为0.001和0.000 1 ng·mL-1。采用该清洗方法,结合密闭高温高压溶样,测定了24个国际地质标样中的Bi和Sb。大部分标样的测定结果与已有参考值吻合较好。文章还给出了国际标样AGV-2(安山岩)、BHVO-2(玄武岩)和BCR-2(玄武岩)中Bi和Sb的测定值。     

单原子Bi吸附对BiOI光催化性能的影响

BiOI是一种极具潜力的光催化剂,目前其光催化效率较低,有待进一步提高.本文为了研究其微观光催化机理,提高光催化性能,采用第一性原理方法计算研究单原子Bi吸附在1I-BiOI表面体系的结构、电子和光学性质.与BiOI相比,Bi/BiOI吸附体系不仅结构稳定性强,而且具有可见光吸收高的性质.计算结果表明,单原子Bi吸附在1I-BiOI表面时,电荷从吸附原子Bi转移到1I-BiOI表面,与1I-BiOI体系相比,吸附Bi的1I-BiOI体系中Bi-B、Bi-Z和Bi-H的功函数降低,单原子Bi吸附后,Bi/BiOI体系的光吸收增强.表明吸附原子Bi与1I-BiOI之间形成了内建电场,提高了电子转移效率,抑制了光电子-空穴复合率,进而提高光催化性能.计算研究表明单原子Bi吸附能提高BiOI光催化效率,有助于设计具有更好光催化性能的新型结构.