非晶态超导合金Zr87.7Si12.3中结构弛豫和结晶化对超导

对非易态超导合金Zr_87.7Si_12.3,在适当的温度下进行了lh等时退火处理.测量了其结构、超导临界参量T_c,H_(C2)及其转变宽度ΔT_c,ΔH_c2等的变化.发现些与金属-金属型非晶态合金不同的变化规律,并结合在结构弛豫过程中所发生的拓扑短程有序化和化学短程有序化,以及相应的结晶化机制,对实验结果作了讨论. 关键词：     

非晶Fe82Si5B13合金的磁导率驰豫

在0—300℃范围内考查了非晶Fe₈₂Si₅B₁₃合金的磁导率等温弛豫动力学行为,给出了等时弛豫谱,观察到四个弛豫峰。测量表明,总的磁导率弛豫由两种弛豫过程组成,即对于退磁可逆的普通减落和对于退磁不可逆的磁导率连续衰减。计算了弛豫时间和激活能的分布,表明弛豫时间和激活能有宽的分布。普通减落和磁导率衰减过程的最可几激活能分别为1.0eV和1.4eV。对退火的样品,观察到磁导率先是增大而后是衰减的广义cross-over效应。 关键词：     

YBa2-xSrxCu3O7-δ系统的超导电性与结构的关联

本文系统地研究了YBa_2-xSr_xCu₃O_7-δ中超导电性与物相以及结构变化之间的关系。发现当0c并不随Sr的含量而单调变化。在x=1.0处,T_c出现一峰值。同时,超导临界温度与样品的晶体结构之间呈现出强烈的相关性:随着正交性的增强(即a,b间差值的增大),T_c单调地上升。本文还就S 关键词：     

C-15结构(Hf,Zr,Ta)V2和(Hf,Zr,Nb)V2合金超导转变的压力效应研究

本文研究了C-15结构化合物(Zr_0.5Hf_0.5-xTa_x)V₂(x≤0.2)和(Hf_0.5Zr_0.5-xNb_x)V₂(x≤0.2)的超导转变温度T_c及其压力效应?T_c/?P。报道了实验方法与结果。与(Hf_1-xTa_x)V₂和(Zr_1-xTa_x)V₂的情况不同,在(Zr_0.5Hf_0.5-xTa_x)V₂中Ta的引入使常压下的T_c下降,然而(?)T_c/(?)P却大为提高。因此高压下Zr_0.5Hf_0.45Ta_0.05V₂的T_c反而比Hf_0.5Zr_0.5V₂更高。导出了一个基于角动量分波表象能带论方法的描述压力效应的新关系式。它指出导带电子波函数中的高角动量成分变化对T_c的压力效应影响比较重要。这个公式有助于理解上述复杂的实验现象,并能合理地解释某些元素(如Cs,Ba,La等)的T_c随压力剧增的事实。 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：     

(Bi,Pb)2Sr2Ca2Cu3Oy单相样品的超导电性与载流子浓度

对(Bi,Pb)₂Sr₂Ca₂Cu₃O_y单相样品进行不同条件下的热处理,通过X射线衍射、电阻-温度关系、交流磁化率,以及Hall系数等测量,发现样品均具有较好的单相性,随着热处理条件的变化,其超导转变中点温度(T_c)有规律地分布在100—110K之间,T_c随载流子浓度(n_H)的增加而升高。实验结果表明,热处理条件对样品的相结构、超导 关键词：     

BaFCl0.5Br0.5:Sm2+的荧光特性分析

本文是对无机光谱烧孔的典型材料BaFCl_0.5Br_0.5:Sm²⁺的发光动力学过程进行的探索。通过实验得到了⁵D₂、⁵D₁、⁵D₀→⁷F₀的荧光强度、荧光衰减曲线随温度的变化关系,对⁵D₂→4f5d带的热激活、⁵D_J间的无辐射弛豫,⁵D_J→⁷F₀的辐射跃迁等过程进行了分析。     

(Hf0.5Zr0.5V2)Hx的声子谱与超导性的关系

本文报道了用Be过滤探测器谱仪对C-15相的(Hf_0.5Zr_0.5V₂₎H_x等五种样品的声子谱的测量。观察到了它们的声子谱随含氢量而变化以及声学支有规则的软化现象。表明(Hf_0.5Zr_0.5V₂₎H_x的T_c随x的变化,主要是声学支的贡献,声学文软化有利于T_c的提高,而光学支“软化”可能会抑制超导性。 关键词：     

用Monte-Carlo方法计算L12结构的有序度

本文应用Monte-Carlo统计物理计算方法,计算了L1₂结构有序度随温度的变化。计算中考虑了最近邻有序相互作用J₁和次近邻有序相互作用J₂=0,-0.3J₁,0.3J₁三种情况。计算结果显示存在有序无序一级相变,临界温度T_c与准化学方法等理论结果相符,同时发现次近邻有序相互作用J₂敏感地影响到有序无序转变温度T_c,为间隙原子对L1₂结构金属间化合物塑性的作用提供了一种可能的解释。 关键词：     

CeCu2Si2和UBe13的超导理论(Ⅱ)——热力学量的计算

根据文献[1]中给出的模型和能隙方程,计算了超导态的热力学临界磁场,T_c处的比热跃变以及T_c以下的比热行为。结果表明:有关热力学量的临界值与实验结果定性相符;T_c以下的比热行为在整个温区与CeCu₂Si₂和UBe₁₃的实验结果符合。 关键词：     

电子型掺杂高温超导体La2-xCexCuO4飞秒时间分辨动力学研究

利用飞秒时间分辨光抽运探测技术研究了电子型掺杂La_2-xCe_xCuO₄(LCCO)高温超导材料的准粒子超快动力学过程.得到低温(T<0.7T_c)、转变温度附近(0.7T_c≤T≤T_c)和高温(T>T_c)三个温区内的动力学行为.研究发 关键词： 电子型掺杂高温超导体 飞秒时间分辨 准粒子 声子瓶颈     

Dielectric dispersion in the microwave range of the incommensurate phase (NH4)2BeF4

The complex dielectric constant of (NH₄)₂BeF₄ single crystals was measured in the frequency range from 0.6 to 300 MHz in the vicinity of the transition temperature T_c. It was found that, the relaxation frequency is about 1 × 10⁸Hz atT_c. Dielectric relaxation can be described by a polydispersive process.     

Unusual behavior of nuclear relaxation in CeCu2Si2 “possible evidence for triplet superconductivity”

Nuclear relaxation of ⁶³Cu in the superconducting state of the Kondo-lattice system CeCu₂Si₂ has been studied with the use of the ⁶³Cu nuclear quadrupole resonance technique under zero field and down to 65mK. The nuclear spin-lattice relaxation rate (1/T₁) decreases drastically just below T_c=0.67 K down to 0.5T_c without the apparent enchanced behavior and then is found to be almost temperature independent below 0.3T_c. These results suggest that the superconductivity in CeCu₂Si₂ is not in the usual BCS regime. The analysis based upon the existing triplet pairing model with an anisotropic energy gap describes well the behavior from T_c down to 0.5T_c, while the temperature independence below 0.3T_c remains unexplained.     

Dielectric dispersion in the incommensurate phases of [N(CH3)4]2CoCl4 and [N(CH3)4]2ZnCl4

The complex dielectric permittivity ?(ω) of [N(CH₃)₄]₂CoCl₄ and [N(CH₃)₄]₂ZnCl₄ along the a-axis was measured between 0.35 MHz and 100 MHz. It has been found that for both substances the relaxation frequencies are about 5 MHz at T_c. The dielectric relaxation of both substances could be described by a polydispersive process β = 0.74 in the vicinity of T_c. However, for the temperature region of (T?T_c) > 0.6 for [N(CH₃)₄]₂CoCl₄ the dielectric absorption seems to be rather monodispersive.     

Elucidation of 3D-to-2D transformation by magnetization studies for Hc in Bi2Sr2CaCu2O8

New magnetization results (for Hc) on a single crystal of Bi2212 elucidating the transition from a one-component to a two- component response across the 3D-to-2D transformation are reported. The two-component response is identified to emanate from the 2D planes and interplanar links. The magnetization response above the transformation temperature T_s and very close to T_c is found to be irreversible in contrast to the reversible behavior so far believed in. A new phase diagram for the mixed state of layered superconductors near T_c is proposed.     

B NMR relaxation in superconductors: YRuB2 and LuRuB2

To investigate the electronic states in YRuB₂ and LuRuB₂, we have carried out ¹¹B NMR measurements. In the normal state, the spin-lattice relaxation rates 1/T₁'s in these compounds are proportional to the temperature T. 1/T₁'s show a small coherence peak just below the superconducting transition temperature T_c and decrease exponentially well below T_c. YRuB₂ and LuRuB₂ are found to be BCS superconductors with the energy gap 2Δ(0)=3.52 k_BT_c.     

Two-dimensional critical behaviour in antiferrodistortive Al ur6(CIO4)3 and Ga ur6(ClO4)3

Critical behaviour with dimensionality d = 2 has been observed for the 300 K antiferrodistortive phase transition in Al ur₆(ClO₄)₃ and Ga ur₆(ClO₄)₃ by means of the temperature dependence of the ESR parameter D. The systems exhibited d = 2 behaviour in the static critical behaviour for T<T_c?40 K for T>T_c + 40 K. From the ESR data including line width measurements the local order parameter relaxation rate ω₁ has been obtained for various temperatures above T_c, with a lowest value of ω₁ = 150 MHz at T_c + 15 K     

Electrical and infrared study of Bi2Sr2Ca1Cu2O8 in semiconducting, superconducting ceramic and superconducting glass ceramic state

We have studied the electrical and infrared properties of Bi₂Sr₂Ca₁Cu₂O₈ compound in three states. Electrical and IR measurements show that the pure powder state sample is a semiconductor, the ceramic Bi₂Sr₂Ca₁Cu₂O₈ sample prepared after annealing at 820°C for 240 hours shows a T_c of 85 K, whereas Bi₂Sr₂Ca₁Cu₂O₈ sample prepared through glassy route, i.e. melting at 1250°C and annealing at 820°C for 240 hours shows a drop of T_c by 5 K. The infrared spectra of superconducting ceramic and glass ceramic states in the available frequency range of measurement reveals the presence of three phonons. Since the vibrational mode around 595 cm^–1 is due to CuO₂ layers and as the CuO₂ layers are responsible for T_c in the ceramic superconductors, any change in these layers will affect the T_c. The shifting of the 595 cm^–1 mode towards lower frequencies in the glass ceramic due to different preparation process, indicates that there is a change in CuO₂ layers resulting in a change of T_c, which is confirmed by Four probe dc measurements.     

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：     

Proton spin-lattice relaxation study of the phase transition in TlH2AsO4

Measurements of the temperature and frequency dependence of the proton laboratory and dipolar frame spin-lattice relaxation rates in powdered TlH₂AsO₄ demonstrate that the ⁷⁵As quadrupole resonance frequency changes from v_Q ≈ 38 MHz at T ?T_c to v_Q 〈 10 MHz at T 〉 T_c. The structural phase transition at T_c = 251 K is thus connected with a disordering of the protons in the O–H … O bonds surrounding the AsO₄ groups.