Anisotropy of Iodine Intercalated Bi2212 Single Crystals by Magnetic Torque

The magnetic torque of iodine intercalated Bi₂Sr₂CaCu₂O₈₊ (I-Bi2212) single crystals has been measured under magnetic fields up to 8 kOe in the temperatures from 4.2 to 100 K. The anisotropy parameter for the 1-Bi2212 determined by London model is smaller than that for the pure Bi₂Sr₂CaCu₂O₈₊ (Bi2212). A sharp peak C1 due to the intrinsic pinning and an extra peak C2 due to the dimensional crossover of the pancake vortex are observed in the magnetic field direction dependence of the torque. The reduced temperature at which the peak C1 appears with decreasing temperature is T/T _c=0.82, which is lower than T/T _c=0.97 for the pure Bi2212. The dimensional crossover field for the I-Bi2212 obtained from the peak C2 is larger than that for the pure Bi2212. According to these results, it is concluded that the iodine intercalation causes the enhancement of interlayer coupling.     

Resistivity and Hall Coefficient of Zinc Diarsenide at Hydrostatic Pressures of up to 9 GPa

The electrical properties of ZnAs₂ single crystals were measured along the [001] direction in the pressure range from 0 to 9 GPa. The electrical resistivity of the crystals was found to decrease by one order of magnitude as the pressure increases from 0 to 7 GPa, without significant changes at higher pressures. The Hall coefficient drops by two orders of magnitude as the pressure increases from 0 to 7 GPa and remains constant in the range from 7 to 9 GPa.     

Hall Effect in Bulk‐Doped Organic Single Crystals

The standard technique to separately and simultaneously determine the carrier concentration per unit volume (N , cm^?3) and the mobility (μ) of doped inorganic single crystals is to measure the Hall effect. However, this technique has not been reported for bulk‐doped organic single crystals. Here, the Hall effect in bulk‐doped single‐crystal organic semiconductors is measured. A key feature of this work is the ultraslow co‐deposition technique, which reaches as low as 10^?9 nm s^?1 and enables us to dope homoepitaxial organic single crystals with acceptors at extremely low concentrations of 1 ppm. Both the hole concentration per unit volume (N , cm^?3) and the Hall mobility (μ_H) of bulk‐doped rubrene single crystals, which have a band‐like nature, are systematically observed. It is found that these rubrene single crystals have (i) a high ionization rate and (ii) scattering effects because of lattice disturbances, which are peculiar to this organic single crystal.     

Elastic Anisotropy,Isothermal Compressibility,and Gruneisen Parameter of GaS Single Crystals

The elastic anisotropy factor, isothermal compressibility, and Gruneisen parameters of GaS single crystals are determined in the range 80–410 K. With increasing temperature, the anisotropy factor and volume compressibility of GaS increase, while its Gruneisen parameters decrease. The results are interpreted in terms of the anharmonicity of lattice vibrations.     

Second and Third Peaks in the Non-resonant Microwave Absorption Spectra of Superconducting Bi2212 Crystals

Non-resonant microwave absorption (NMA) measurements at liquid nitrogen temperature with systematic microwave power variation showed a two-peak structure in the Bi-2212 textured crystals, similar to that observed in the Bi-2212 single crystals (Srinivasu et al., in J. Supercond. Incorp. Nov. Magn. 14:41, 2001). NMA signals from the aged Bi-2212 single crystals show an emergence of a ‘third peak’ as a function of microwave power. We qualitatively interpret these second and third peaks as due to the microwave power induced phase locking of several number of junctions into coherent groups and then the destruction of the phase locking by the applied DC field leading to decoupling or fluxon motion, which gives the loss in individual junctions belonging to these otherwise coherent groups.     

Time-Temperature Dependence of Anisotropy of Creep-Rupture Strength Characteristics of Single Crystals of Nickel-Base Superalloys

The paper presents the results of processing experimental data on creep-rupture strength of >110<- and >111<-oriented single crystals of ZhS36 and CMSX-4 nickel-base superalloys in the temperature range from 1023 to 1373 K. We give numerical values of the coefficients in equations of the time-temperature dependence of creep-rupture life and plot the creep-rupture strength curves for single crystals of the same orientation in the creep-rupture life range up to 105 h. We have revealed three various time-temperature regions of variation of the creep-rupture strength anisotropy factor, where the mode of anisotropy is governed by various creep mechanisms and depends on the microstructure evolution of single crystals.     

Explanation of Non-linear In-Plane Resistivity and Hall Coefficient in the Normal State of Cuprates: Polaronic Approach

We present a theoretical study of the in-plane resistivity ρ _{a b} (T) and Hall coefficient R _H (T) within the polaronic model and precursor pairing scenario by considering a two-component charge carrier picture in the normal state of high-temperature superconducting cuprates (HTSC). Here, we use a Boltzmann-equation approach and extended BCS-like model to compute ρ _{a b} (T) and R _H (T) in the τ-approximation. The opening of the pseudogap (PG) in the normal state of the cuprates should affect their transport properties. We have found that the transition to the PG regime and the effective conductivity of charge carriers in the normal state are responsible for the pronounced non-linear temperature dependence of ρ _{a b} and R _H . With the two-component model analysis, we conclude that the opening of the BCS-like PG, while the non-linear temperature dependence of ρ _{a b} and R _H could be understood as a consequence of pairing fluctuations in the PG state of cuprate superconductors. The calculated results for ρ _{a b} (T) and R _H (T) were compared with the experimental data obtained for various hole-doped cuprates. For all the considered cases, a good quantitative agreement was found between theory and experimental data. We also show that the energy scales of the binding energies of charge carriers are identified by PG crossover temperature on the cuprate phase diagram.     

Resistivity Tensor in the Normal State of BSCCO Single Crystals as a Function of Doping

We present measurements of the resistivity tensor of Bi₂Sr₂CaCu₂O₈+ single crystals with different oxygen concentrations. Sample doping varies from underdoped to slightly overdoped. Measurements are performed through multiterminal technique, which allows for a simultaneous determination of both in-plane and out-of-plane components of the resistivity tensor. Data are analyzed in terms of a model that assumes two different mechanisms for the out-of-plane conduction, markedly thermal activation and incoherent tunneling. Within this model we are able to describe data of normal state resistivity for all samples with different doping levels. We also analyze data from the literature. In all cases, the proposed model describes very well the data in the normal state.     

Nonresonant Microwave Absorption in Bi2212 Single Crystal: Second Peak and Microwave Power Dependence

Nonresonant microwave absorption (NMA) measurements were carried out at liquid-nitrogen temperature on a high quality Bi2212 single crystal, as a function of microwave power in three mutual orientations of crystal ab plane, dc field (H_dc), and microwave magnetic field (H_w). NMA line shapes in Bi2212 crystal are complicated with a narrow peak (P₁ peak) located near zero field, followed by a much broader second peak (P₂ peak) in the particular orientations. More excitingly, we show that the P₂ peak qualitatively evolves as a function of microwave power in the orientation of H_dc ab plane, plane, and H_dc H_w. In this configuration, as the microwave power is progressively increased, the broad P₂ peak first gets smeared off and then a multiple peak structure appears, which develops into another narrower second peak (P_s-peak) at high enough microwave powers. In the orientation of plane, H_w ab plane, and H_dc H_w, we report for the first time the appearance and disappearance of a new second peak (P₂-like peak) as a function of microwave power.     

Effects of Neutron Irradiation and Annealing on the Elastic Moduli and Electrical Resistivity of Molybdenum and Tungsten Single Crystals

The effects of neutron irradiation and annealing on the elastic moduli and electrical resistivity of Mo and W were studied using single-crystal samples oriented with their axis along [100], [110], and [111]. The samples were irradiated with fast neutrons (E> 0.1 MeV) to a neutron fluence of 1.14 × 10²⁶n/m²in a BR-10 reactor at 460°C. The irradiation-induced changes in resistivity and elastic moduli were found to be orientation-dependent. Irradiated W was found to exhibit elastic anisotropy and relaxation of the shear and Young's moduli. Isochronal annealing below 0.7t _mdid not reduce the resistivity of the samples to its initial level, presumably because of the formation of radionuclides, while the shear and Young's moduli were restored to their initial levels.     

Longitudinal and Hall Resistivity in Thin Film Superconductor

We associate both the longitudinal and Hall resistivity of a thin film superconductor YBCO near its transition temperature with vortex lattice melting. In a two dimensional Kosterlitz-Thouless transition there are two characteristic properties, the number of free dislocations and the dielectric function for the dislocation pairs. Using these two parameters, we are able to fit both the longitudinal and Hall resistivity as a function of temperature and magnetic field.     

Structural and Transport Properties of Sn-Doped Bi2Te3 – x Se x Single Crystals

The transport properties of Bi_{2 – y} Sn _y Te_{3 – x} Se _x solid solutions are studied. The results demonstrate that doping with Sn has a strong effect on the temperature dependences of the thermoelectric power and electrical conductivity of the crystals. This suggests that the valence band of the crystals contains Sn-related resonance states. The point defects and dislocation system in Bi₂Te₃ and Bi_{2 – y} Sn _y Te_{3 – x} Se _x solid solutions are studied by transmission electron microscopy. It is shown that the predominant defects in the crystals studied, grown by the Czochralski technique, are dislocations lying in the (0001) plane. The estimated dislocation density is 10⁸ to 10⁹ cm^–2, and the primary slip plane is (0001). Electron-microscopic examination indicates the presence of stacking faults and very small dislocation loops in both Bi₂Te₃ and Bi_{2 – y} Sn _y Te_{3 – x} Se _x single crystals. Since all of the crystals are highly degenerate semiconductors, it is reasonable to assume that structural defects have an insignificant effect on their electrical properties.     

Anisotropy of the Thermal Conductivity of Parahydrogen Crystals

The anisotropy of thermal conductivity of parahydrogen crystals has been observed for the first time. The thermal conductivity measurements have been made on samples of different diameters at the temperature range from 2 to 8 K.     

Effect of Pressure on the Out-of-Plane Critical Current and T c of Bi-2201 and Bi-2212 Single Crystals

We used the hydrostatic pressure P <1 GPa as a tool to change the c-axis critical current (interlayer coupling) of Bi-2201 and Bi-2212 single crystals. The c-axis critical current drastically increases with pressure (up to 270 % GPa ^–1 ). The superconducting critical temperature, on the contrary, only slightly increases with a rate of 2-6 % GPa ^–1 . This implies that the CuO-interlayer coupling has little effect on T _c in Bi-compounds.     

Na1.88Bi1.88S4和Na1.36Ca1.28Bi1.36S4单晶制备与结构及其光学性能表征

采用碘化钠为助熔剂,通过固相反应法制备了两种晶体质量较好的Na_1.88Bi_1.88S₄和Na_1.36Ca_1.28Bi_1.36S₄单晶。测试结果表明,它们属于氯化钠结构,面心立方,空间群为Fm-3m。形貌表征和物性测试结果表明,在碘化钠的作用下,化合物Na_1.88Bi_1.88S₄和Na_1.36Ca_1.28Bi_1.36S₄呈现双锥状形貌,沿(111)晶面择优取向生长,带隙分别为1.29和1.45 eV。通过光电器件性能测试,发现两种化合物均表现出良好的光电响应特性,说明它们可以作为一类潜在的、性能优良的光电开关材料。     

Growth of Sillenite-Structure Single Crystals

The main processes for preparing bulk single crystals and films of photorefractive and piezoelectric Bi₁₂M _x O_20±δ (M = Group II–VIII elements) sillenite compounds are considered. Experimental data are summarized on the crystal growth of Bi₁₂M _x O_20±δ from the melt and under hydrothermal conditions, and the key morphological features of sillenites are analyzed. Various types of macroscopic growth defects in sillenite-type crystals are described, and their origin is discussed. The compositions of second-phase inclusions in undoped and doped (Group I–VIII elements) Bi₁₂SiO₂₀, Bi₁₂GeO₂₀, and Bi₁₂TiO₂₀ single crystals are presented, and the main physicochemical properties of various Bi₁₂M _x O_20±δ crystals are summarized.     

Effect of Heat Treatment on the Superconductivity of Pb-Doped Bi-2212 System: Evidence for a Possible Phase Segregation

Samples of the Bi_1.8Pb_0.2Sr₂CaCu₂O_8– system with different oxygen concentrations were prepared by annealing the corresponding ceramic sample in various conditions. The normal-state properties were investigated by means of X-ray diffraction (XRD), resistivity, thermoelectric power (TEP), and specific heat. Analyses of these data demonstrate that a possible phase segregation exists in some samples, i.e., the Bi_1.8Pb_0.2Sr₂CaCu₂O_8– phase with lower carrier concentrations separates into oxygen-rich superconducting domains and oxygen-poor superconducting domains. The anomalous properties of the normal state are discussed in the paper.     

Negative Temperature Coefficient of Resistivity in Bulk Nanostructured Ag

1. IntroductionIn 1980s, Glener et al.11'2] studied the relationshipbetween resistivity and temperature for nanocrystalline metals (such as Cu, Pd and Fe) and the changerule of the temperature coefficient of resistivity (or)with the grain size. It was shown that the resistivityincreases linearly with temperatuxe (the Mathiessenrule). This is similar to what appears in the relativelypure ordered metals with coarse grains. The decreaseof a with the drop of the density was reported inthe nanost…     

Growth and Study of Borocarbide Single Crystals

Superconducting yttrium borocarbides were synthesized by different methods. A two-step method was found to be advantageous. Influence of the annealing time on superconducting properties is investigated. The superconducting temperature of YNi ₂ B ₂ C single crystal is 15 K.