A STUDY OF RAMAN SCATTERING AND INFRARED ABSORPTION SPECTRUM IN A NEW SERIES OF MERCURY-BASED HIGH-Tc SUPERCONDUCTOR (Hg,Mo)Sr2(Y1-xCax)Cu2O6+δ

Lattice vibrations of the (Hg,Mo)Sr₂(Y_1-xCa_x)Cu₂O_6+δ—a new series of mercury-based high-T_c superconductor are analyzed with the aid ofgroup theory. The vibrations of species are given. They are 4A_1g+ B_1g+ 5E_g+ 7A_2u + B_2u+ 8E_u. The 4A_1g, B_1g and 5E_g modes are Ramma active, the 6A_2u and 7E_u are infrared active. Phonon vibration characteristics of the samples are studied using Raman scattering and infrared absorption spectra. The experimental results show that the typical phonon vibrational modes appear mainly at 145, 320, 440, 578, 592 and 645cm^-1, The intensities of the 145, 320, 440, 578 and 645 peaks decrease with increasing Ca content x and the position of 645 peak moves to higher wavenumber slightly. In this article, the phonan modes are assigned and their variation behavior with increasing Ca content x are discussed.     

POSITRON LIFETIME STUDIES OF Y1-xCaxBa2Cu3O7-δ AND Y1-xCaxBa2Cu3-xFexO7-δ

In this paper it is reported that the measurement of the bulk positron lifetime as a function of substitution content x in the temperature range from 70 to 220K was performed in two high-T_c superconducting systems, Y_1-xCa_xBa₂Cu_3-xFe_xO_7-δ and Y_1-xCa_xBa₂Cu₃O_7-δ. It was found that τ_B of both systems decreases significantly with x and the temperature dependence of τ_B is very weak in normal state. In lower temperature region (Tc), a dramatic x-dependent temperature variation of τ_B was observed in the Ca-substituted system: from a decrease of τ_B with decreasing T to an increase of τ_B. With increasing x, the temperature dependence of τ_B remains weak in the Ca- and Fe- substituted systems. Compared with the experimental data of positron lifetime in other substituted systems and the calculation of the positron density distribution, the authors suggest that positron bulk lifetime spectra behaviour can be interpreted by the physical model based on the transfer of electron density between the CuO₂ planes and Cu-O chains. Therefore, the study of positron lifetime spectra provides a useful means to detect the local charge density and to study the correlation between the electronic structure and the high-T_c superconductivity.     

RAMAN SCATTERING OF α-ET3(ReO4)2 CHARGE-TRANSFER SALT

We describe the results of Haman studies on C=C stretch modes in α-ET₃(ReO₄)₂ charge-transfer salt with the incident laser beam polarised perpendicular and parallel to the large flat face of plate-like crystal. We have assigned central C=C stretch mode at 1454 cm^-1 and ring C=C stretch mode at 1470cm^-1. The change in ring C=C stretch vibration was observed at the metal-insulator transition of α-ET₃(ReO₄)₂ on warming due to the distortion of the ET molecules.     

Y1-xCaxBa2Cu3-xMxO7-δ (M=Fe,Ni)体系的超导电性

本文报道,通过对Y_1-xCa_xBa₂Cu_3-xMxO_7-δ(M=Fe,Ni)体系样品的晶体结构、氧含量、正常态电阻率与温度的关系,以及超导转变温度等测量,并与YBa₂Cu_3-xMxO_7-δ(M=Fe,Ni)体系进行比较,发现Y_1-xCa_xBa₂Cu_3-xFe_xO_7-δ体系的T_c显著地高于相应x值的YBa₂Cu_3-xFe_xO_7-δ体系,而Y_1-xCa_xBa₂Cu_3-xNi_xO_7-δ体系则相反,T_c低于仅Ni替代的体系,表明Ca和Fe同时替代时两者引起的载流子浓度(n_H)变化相互补偿,抑制了仅Fe替代时引起的n_H和T_c急剧下降;而作Ca和Ni同时替代时主要的不是两者引起载流子浓度变化的相互补偿,Ca和Ni替代效应之间的关联较弱。作者认为,对Y_1-xCa_xBa₂Cu_3-xFe_xO_7-δ体系属于CuO₂平面外的元素替代,这时载流子浓度是决定Tc的主要因素;而对Y_1-xCa_xBa₂Cu_3-xNi_xO_7-δ体系,由于Ni²⁺离子主要占据Cu(Ⅱ)位,它导致磁拆对效应,Ni²⁺离子的拆对效应是引起T_c下降的直接原因。 关键词：     

A POSSIBLE SOLITON-LIKE POLARON MODEL FOR SUPERCONDUCTORS Y1-xCaxBa2Cu3-xMxO7-δ(M=Fe, Ni)

Using 1+1 soliton-like polaron model of a deformable continuum, the critical temperature and the energy gap in high-temperature superconductors Y_1-xCa_xBa₂Cu_3-xM_xO_7-δ(M=Fe,Ni) are studied in the framework of finite temperature Green's function theory. The ratio 2Δ/k_BT_c=3.9 is obtained. Theoretical results are found in good agreement with the experimental data.     

A STUDY ON ABSORPTION OF Na ATOMS ON Si(100) 2×1 SURFACES WITH DV-Xα METHOD

The Na absorption on Si(100) 2×1 surface is studied with quantum chemistry molecular cluster method. The calculated results show that the most favourable absorption site of Na is the cave site and the charge transfer of Na atom to Si is large when the Na coverage is smaller than 0.5 monolayer (ML). A Na chain is formed along the cave sites at the 0.5 ML Na coverage, the charge transfer then becomes small. The calculated density of states show that the Na atoms are metallic along the chain. At 1 ML coverage, the Na atoms occupy both the cave and pedestal sites and form a double-layer. There is a charge transfer of 0.5e from each Na atom to the Si surface. The calculated surface energy shows that the saturation absorption of Na on Si surface is 1 ML.     

Y2(Fe1-xSix)14B的中子衍射研究

Nd₂Fe₁₄B是一种磁能积很高的优良的永磁材料,但在实用上稍嫌它的居里温度低了一点。为了提高它的居里温度,人们曾用某些元素替代其中的一些铁作了尝试。文献[9]及我们最近的实验表明:用硅代替部分铁之后,材料的居里点都获得了提高。本文用中子衍射法研究了Si在Y₂Fe₁₄B中的占位情况,以了解Si对磁性能产生的影响。中子衍射的结果表明:Si择优地占据c,j₁及k₂晶位。最后,用磁交换作用对结果进行了讨论。 关键词：     

Y1-xPrxBa2Cu3O7+δ的红外反射谱

测量了温度范围为4.2—300K的Y_1-xPr_xBa₂Cu₃O_7+δ(x=0,0.1,0.2,0.4,0.5,0.61.0)的红外反射谱,发现在低温下Ba模有双模行为,随着x值增大双模强度反转,在YBa₂Cu₃O_7+δ中已被判定为Y模的位于194cm^-1的反射峰的位置与Pr的含量无关,即用Pr部份或全部替代Y时此峰不发生频移。建议Pr在Y_1-xPr_xBa₂Cu₃O_7+δ,中是正4价,Pr的替代使原来可移动的空穴被定域在Pr的周围,使超导电性受到压制。 关键词：     

LECTRONIC STRUCTURE STUDIES OF Bi2Sr2CaCu2-xSnxO8+δ SYSTEM

Photoemission measurements have been carried out for Bi₂Sr₂CaCu_2-xSn_xO_8+δ system with conventional x-ray photoemission spectroscopy for core-level spectra and synchrotron radiation photoemission spectroscopy for valence band. With Sn doping, all core levels shift differently in binding energy, and the intensity near fermi energy becomes smaller in valence hand. From the experiment, we can deduce that the shifts of all core levels and valence hands may involve some other mechanisms, such ms electrostatic effects, in addition to binding energy referencing effects. We argue that the chemical environment plays a crucial role in the electronic structure of high-temperature superconductors.     

Y1-xCaxBa2Cu3O6系统中空穴掺杂诱导的绝缘体-金属转变和超导电性

本文报道利用Ca部分取代Y的方法,将空穴引入绝缘的YBa₂Cu₃O₆系统中,使其发生由绝缘体到超导体的转变,并通过研究其电子输运性质、磁性质,以及晶体结构的变化,揭示了具有适当载流子浓度的CuO面是维持高T_c超导电性的重要条件。 关键词：     

金属玻璃(Cu1-xNix)33Zr67合金的低温电阻率

本文研究了金属玻璃(Cu_1-xNi_x)₃₃Zr₆₇合金的低温电阻输运特性。在较宽的温区(2—273K)测试了电阻率,测量结果符合Mooij判据。样品电阻率随温度的变化行为与双能级隧道模型符合较好。 关键词：     

阴离子取代合成Sr3LaAxV3-xO12:Eu3+(A=Mo,W)白光荧光粉

通过高温固相法合成Sr₃LaA_xV_3-xO₁₂:Eu³⁺（A=Mo,W）荧光粉,利用MoO₄^2-和WO₄^2-取代基质中部分VO₄^3-,改变基质组成和结构,进而影响基质和激活剂Eu³⁺离子的发光性能。采用X射线衍射（XRD）、扫描电子显微镜（SEM）和荧光分光光度计对所合成样品的物相、形貌、荧光性能及荧光寿命进行表征。研究表明,MoO₄^2-和WO₄^2-的部分掺杂对基质发光位置和强度均有影响,能明显减弱VO₄^3-的发光,但对Eu³⁺离子发光影响不大,添加电荷补偿剂F^-可以加强VO₄^3-对Eu³⁺离子的能量传递。通过调整基质VO₄^3-发光和Eu³⁺离子发光,可以得到单一基质的白光荧光粉。初步探讨了阴离子掺杂对Eu³⁺离子红光发射增强的机理。     

YBa2(Cu0.95M0.05)3O7-δ的代换效应及其中子衍射研究

X射线衍射实验表明YBa₂(Cu_0.95M_0.05)₃O_7-δ(M=Ti,V,Cr,Mn,Fe,Co,Ni,Cu和Zn)均为单相结构。Fe,Co,Ni和Zn对Cu的替代使超导临界温度T_c显著下降,而同样含量的Ti,V,Cr,Mn对Cu的替代并未对超导性能产生显著影响。并利用中子衍射分析了Ti,Mn,Fe和Co对Cu原子的取代,发现代换原子对Cu的两个晶位各自存在不同的择优占据 关键词：     

第2系列ZrO2(Y2O3)薄膜的慢正电子研究

用慢正电子技术研究了在溅射时不加偏压,衬底加热300℃,纯Ar气氛下制备的用Y_{2O3稳定的ZrO2薄膜材料(简称YSZ薄膜),发现了YSZ薄膜在不同 深度处的缺陷分布情况,退火温度对YSZ薄膜缺陷有影响.简要讨论了致密、优质YSZ薄膜的 制备方法.}     

YBa2Cu1-xCox(Cu1-yZny)2Oz体系的Co,Zn共同掺杂效应

本文报道通过对YBa₂Cu_1-xCo_x(Cu_1-yZn_y)₂O_z(0≤x,y≤0.1)体系晶体结构、氧含量、正常态电阻-温度关系、Hall效应以及超导临界温度等的综合测量,发现随着Co和Zn含量的增加,体系经历了从正交结构的超导金属向四方结构的非超导半导体的转变,超导临界温度T_c和载流子浓度n_h均迅速下降,Co 关键词：     

正磷酸盐晶体Ba3(PO4)2和Sr3(PO4)2高温拉曼光谱研究

测量了碱土金属正磷酸盐Ba₃(PO₄)₂和Sr₃(PO₄)₂常温及高温拉曼光谱, 对拉曼振动模式进行指认, 并分析了晶体拉曼振动光谱及晶体结构在高温下的变化. 在温度升高的过程中, 拉曼振动频率向低频移动且振动峰宽度展宽, 晶体中的P-O平均键长随温度升高而变长, 但O-P-O的键角并未发生变化. 晶体在900 ℃以下无结构相变发生. 关键词： 3(PO₄)₂和Sr₃(PO₄)₂')" href="#">Ba₃(PO₄)₂和Sr₃(PO₄)₂ 高温拉曼光谱 振动模式 高温结构     

新块材超导体Pr1-xCaxBa2Cu3O7-δ(0.4≤x≤0.6)的高压合成与超导电性

采用高温高压合成方法，合成出了Pr_1-xCa_xBa₂Cu₃O_7-δ(0.4≤x≤0.6) 系列块材超导体，在缺氧的Pr_0.5Ca_0.5Ba₂Cu₃O_7-δ四方123结构样品中得到了T_c为98K.实验结果表明Pr在123结构中的价态为大于3+的混合价态，因而空穴填充和杂化导致的载流子局域化是Pr抑制123相超导电性的关键因素. 关键词：     

MAGNETIC PROPERTIES OF Pr2Co17-x Mx ( M＝Ga,Si) COMPOUNDS

The influence of Ga or Si substitution for Co on the structural and magnetic properties of Pr₂Co₁₇ compounds is investigated. All samples studied here are single phase and have the rhombohedral Th₂Zn₁₇-type structure. The unit-cell volume is found to increase linearly by the substitution of Ga for Co,but reduce by the substitution of Si for Co in Pr₂Co₁₇ compounds. In Pr₂Co_17-x M_x, the Curie temperature decreases monoto nically with increasing at an approximate rate of 153K per Ga atom and 175K per Si atom. The saturation magnetic moment of Pr₂Co_17-x M_x ( M=Ga,Si) decreases with increasing x. The rates of the decrease are larger than that expected as a simple dilution. For Pr₂Co_17-xSi_x ,the spin reorientation transition is observed above room temperature. The spin-reorientation temperature Tsrfirst decreases with increasing Si content and then increases at higher x values (x>2). The spin reorientat ion behavior is interpreted by the competition between the Pr and Co sublattice anisotropies. The easy magnetization direction in Pr₂Co_17-xGa_x compounds is perpendicular to the c-axis, and no spin reorientation transition is observed.     

PHASE TRANSITIONS IN Bi2Sr2(Cu1-zFez)O6+δ

We have investigated, by X-ray diffraction, a series of single crystals of Bi-based oxides with the nominal composition Bi₂Sr₂(Cu_1-zFe_z)O_6+δ(0≤z≤0.55). In this system we observed two structural phase transitions with the increase of the doping content. The first transition, from an incommensurate monoclinic phase to an incommensurate orthorhombic phase, occurs at a doping content of iron z_Fe=0.027. The second one corresponds to a phase transition from an incommensurate orthorhombic phase to a commensurate orthorhombic phase at z_Fe=0.34. The comparison of these results with those for more limited substitutions of Zn and Ni indicates the significant role of the insertion of the extra oxygen in the (Bi-O)_∞ double layers.     

SIMS STUDY OF OXYGEN SPIRAL DIFFUSION C-TEXTURED Yba2Cu3O7-δ/SrTiO3 EPITAXIAL THIN FILM

Secondary ion mass spectroscopy was used to study the chemical diffusivity of 0¹⁸ in c-textured YBa₂Cu₃O_7-δ/SrTiO₃ epitaxial thin film. By fitting experimental data to the one- dimensional diffusion curve, the apparent diffusivity along the c-axis was obtained to be equal to l.02×10¹⁴cm²/sec when the temperature was 350℃. A computer analysis method was put forward to calculate the "spiral diffusion" process, and the diffusivity anisotopy of films with different mosaic size obtained. For a film of 7000×7000?² mosaic size, Dab was found to be ～3.55×10^-5xexp((-1.03 ev)/kT) cm²/sec. The calculated results reveal that the variation of the results of Dc is not the result of diffusivity anisotropy but of the difference in mosaic size.