Anomalies in Noble-Metal-Based Liquid Alloys

Experimental data on liquid noble-metal-based alloys were analysed in terms of a pseudopotential approach. The anomalies in the heat of mixing, the electrical resistivity and the magnetic susceptibility were found to be reflected by the theory in a qualitative manner even if compound formation or short range order is not taken into account. The emphasis was placed on liquid Ag-In, but other examples of this particular class of alloys were also included in the discussion.     

高密度电法在涌水区探测中的应用研究

地铁建设中,隧道掘进时容易发生涌水、涌沙等突发事件。在突发状况下,现场情况比较复杂,各种电磁干扰及人为干扰较大。如何克服多干扰,利用先进的物探技术,第一时间为事故处理提供详实可靠的成果是关键问题。综合分析后选择大功率高密度电法进行探测,及时准确的圈定了漏水影响区域范围及空间位置并指导注浆;通过注浆前后成果的对比,及时检验了注浆加固的效果,注浆止水效果良好。在快速应对处置涌水中起到了重要的作用。     

Effects of micro-additions on structures and properties of rapidly solidified Sn-10% Sb alloy

Structure, electrical resistivity, hardness, internal friction and elastic modulus of Sn-10% Sb and Sn₈₉Sb₁₀M₁ (M₁ = Ag, Cu, Zn and Pb) alloys have been investigated. No obvious change on the electrical resistivity value was found at 293 °K of a Sn-10% Sb alloy by adding Zn and Cu, but extreme changes occurred after adding Ag and Pb. The elastic modulus, internal friction, hardness and thermal diffusivity values are greatly affected by adding the micro-additions to a Sn-10% Sb rapidly solidified alloy. It is also interesting to note that Ledbetter's theoretical values of μ/E are in good agreement with the experimental results. The rapidly solidified alloys Sn₉₀Sb₁₀ and Sn₈₉Sb₁₀Ag₁ have good properties as toxic-free lead solder alloys for high-temperature applications and good mechanical properties such as under the hood in the automobile and avionics systems. Also, the rapidly solidified alloys Sn₈₉Sb₁₀Zn₁, Sn₈₉Sb₁₀Cu₁ and Sn₈₉Sb₁₀Pb₁ have good properties as bearing materials.     

Electrical and electronic properties of nitrogen doped amorphous carbon (a-CNx) thin films

Nitrogen-doped amorphous carbon thin films (a-CN_x) were prepared on silicon substrate by pulsed laser deposition process using methane (CH₄) and nitrogen (N₂) as source gas. The electrical properties of a-CN_x films changes with nitrogen concentration in the film structure. The intensity ratio of the D and G peak (I_D/I_G) increases with higher nitrogen concentration, which means that sp²-clusters were formed in these films and is responsible for the enhancement of conductivity of the a-CN_x films. We observed that the amorphous carbon (a-C) films becoming more graphitic in nature yielding higher conductivity/lower resistivity with increase of nitrogen concentration. Electron field emission result shows that the emission current density enhances with nitrogen doping that indicates the useful in electron field emission devices application.     

Effects of Ag addition on phase transformation and resistivity of TiSi2 thin films

In this study, the effects of adding Ag to TiSi₂ thin films are examined. It is demonstrated that both the C49 → C54 transformation temperature and the electric resistivity are appreciably lowered with Ag addition. Due to the presence of Ag nanocrystals precipitated at the C49 grain boundaries, the overall grain boundary density would increase to result in the higher nucleation rate of C54 and the lower transformation temperature. The precipitation of pure Ag network can provide another electric current conductive path except for the TiSi₂ grains. Due to the lower vacuum condition and the higher oxygen content in the current sputtered and annealed films, the C49 → C54 transformation temperature and the resistivity of the TiSi₂-20 at%Ag films can only be reduced by ∼100 °C and 10 μΩ cm, as compared with the non-Ag additive films. With better fabrication vacuum, the transformation temperature and resistivity might be lowered to a level below 700 °C and 15 μΩ cm, which are highly applausive for engineering applications.     

Dependence of resistivity on structure and composition of AZO films fabricated by ion beam co-sputtering deposition

The correlation between the resistivity and the structure/composition in the aluminum doped zinc oxide (AZO) films fabricated by the ion beam co-sputtering deposition at room temperature was investigated. The various compositions of AZO films were controlled by the sputtered area ratio of Al to Zn target. The structure, Al concentrations and resistivities of the as-deposited films were determined by X-ray diffractometer (XRD), energy dispersive spectrometer (EDS) and four-point probe station, respectively. The lowest resistivity of the deposited film was 5.66 × 10⁻⁴ Ω-cm at the 0.7 wt.% aluminum concentration. The most intense ZnO (0 0 2) diffraction peak, the largest grain size, the longest mean free path, and the highest free carrier concentration in the film result in the lowest resistivity of 5.66 × 10⁻⁴ Ω-cm at room temperature; simultaneously, the thermal stability of the resistivity of the AZO film as a function of the sample temperature was investigated. Below 200 °C the film's resistivity was almost kept at a fixed value and the lowest resistivity of 4.64 × 10⁻⁴ Ω-cm at 247 °C was observed.     

Magnetic and transport properties of Nd1.67Sr0.33NiO4

Nd_1.67Sr_0.33NiO₄ polycrystals have been prepared by modified sol–gel method and subsequent annealing. X-ray diffraction analysis, electrical resistivity, magnetic susceptibility and thermal magnetisation have been measured. Rietveld analyses show a tetragonal or pseudo-tetragonal K₂NiF₄-type structure. The resistivity measurements present a change in conduction mode close to 230 K, which corresponds to the charge ordering temperature. Below this temperature, the material adopts a variable range hopping conduction mode; and above, the conduction follows adiabatic thermal activated mode. The magnetic measurements show paramagnetic behaviour in the range of 80–300 K. Moreover, the magnetic susceptibility data show a sign of the charge ordering transition about 230 K.     

Role of mesoscopic morphology in charge transport of doped polyaniline

In doped polyaniline (PANI), the charge transport properties are determined by mesoscopic morphology, which in turn is controlled by the molecular recognition interactions among polymer chain, dopant and solvent, Molecular recognition plays a significant role in chain conformation and charge delocalization. The resistivity of PANI doped by camphor sulfonic acid (CSA)/2-acrylo-amido-1-propane sulfonic acid (AMPSA)/dodecyl benzene sulfonic acid (DBSA) is around 0.02 Ω cm. PANI-CSA and PANI-AMPSA show a metallic positive temperature coefficient of resistivity above 150 K. with a finite value of conductivity at 1.4 K; whereas, PANI-DBSA shows hopping transport at low temperatures. The magnetoresistance is positive (negative) for PANI-CSA (PANI-AMPSA); and PANI-DBSA has a large positive MR. The behavior of MR suggests subtle variations in mesoscopic morphology between PANI-CSA and PANI-AMPSA.     

Metal-insulator crossover in high T c cuprates: A gauge field approach

A metal-insulator crossover appears in the experimental data for in-plane resistivity of underdoped cuprates and a range of superconducting cuprates in the presence of a strong magnetic field suppressing superconductivity. We propose an explanation for this phenomenon based on a gauge field theory approach to the t-J model. In this approach, based on a formal spin-charge separation, the low energy effective action describes gapful spinons (with a theoretically derived doping dependence of the gap m _s ² ∼ δ| ln δ|) and holons with finite Fermi surface (ɛF ∼ tδ) interacting via a gauge field whose basic effect on the spinons is to bind them into overdamped spin waves, shifting their gap by a damping term linear in T, which causes the metal-insulator crossover. The presence of a magnetic field perpendicular to the plane acts by increasing the damping, in turn producing a big positive transverse in-plane magnetoresistance at low T, as experimentally observed.