Effect of varying the ratio of matrix/dispersoid particle size on the piezoresistivity of alumina/carbon-black composite ceramics

Alumina/carbon-black composite ceramics with different percolation thresholds were fabricated by changing the size ratio of constituent particles. The dependence of resistivity on pressure was established for each sample. The compositional dependence of resistivity can be explained by percolation theory. The percolation threshold decreases with increasing alumina/carbon-black particle size ratio. The pressure dependence of the resistivity increases as the composition approaches the percolation threshold. When the relative composition at the percolation threshold is fixed, the sensitivity increases with increasing matrix/dispersoid initial particle size ratio.     

Electrical resistivity of holmium hydride films

The electrical resistivity and temperature coefficient of resistance of polycrystalline holmium hydride films, grown on glass slides, have been measured in vacuo. Experimental results show that the resistivity decreases with decreasing film thickness. The resistivity of 200 Å holmium dihydride film is less than that of the parent metal. The observed behaviour of the thickness dependence of the resistivity has been explained in terms of the structural phase change.     

Effect of deposition process parameters on resistivity of metal and alloy films deposited using anodic vacuum arc technique

Thin solid films of copper, aluminum and nichrome have been deposited on glass substrates with thickness ranging from 20 nm to 200 nm, using the anodic vacuum arc deposition technique. Electrical resistivity and average grain size of deposited thin films have been measured and their dependence on the deposition process parameters has been investigated. Thickness dependence of resistivity has also been compared with numerically generated results using Fuchs-Sondheimer theory and Mayadas-Shatzkes theory which has been found to be in good agreement for film thickness greater than 80 nm. The resistivity values of Cu, Al and NiCr has been found to take a minimum value (approaching that of corresponding bulk material) of 80 A arc current and a substrate bias of around − 50 V.     

Thermoelectric properties of the flash-evaporated n-type Bi2Te2.4Se0.6 thin films

The electronic transport properties of the flash-evaporated n-type Bi₂Te_2.4Se_0.6 thin films have been investigated. The thickness dependence of Seebeck coefficient and electrical resistivity has been analyzed by the effective mean free path model. It was found that both the Seebeck coefficient and the electrical resistivity have a linear relation with the reciprocal of film thickness. The data analyzed by the effective mean free path model have been combined to evaluate important material parameters such as mean free path, its energy dependence, and Fermi energy. Annealing effects on the electronic transport properties have been also examined in conjunction with the antistructure defects. It was found that the annealing treatment is necessary for Bi₂Te_2.4Se_0.6 thin films to reduce the antistructure defects and to improve their thermoelectric properties.     

Electrical properties of lithium-intercalated InSe

We have studied the intercalation reaction of n-type InSe with n-butyl lithium in hexane solution through the time dependence of the electrical resistivity, and by Hall effect measurements. The electrical properties as a function of temperature have also been examined. Li_xInSe resistivity is decreasing as x is increased. The large variation of the resistivity is mainly attributed to the variation of the free carrier concentration in the host material and the semiconducting character is conserved.     

Ferromagnetic- and Superconducting-Like Behavior of the Electrical Resistance of an Inhomogeneous Graphite Flake

We have measured the magnetic field and temperature dependence of the resistivity of several micrometers long and heterogeneously thick graphite sample. The magnetoresistance results for fields applied nearly parallel to the graphene planes show both granular superconducting behavior and the existence of magnetic order in the sample.     

Temperature dependence of the thermal conductivity in nearly magnetic metals: Application to plutonium

In nearly magnetic metals, if one takes into account the temperature dependence of the Stoner susceptibility, then the electron-par-amagnon thermal resistivity, after the low-temperature enhanced linear T behavior, goes through a maximum around the spin-fluctuation temperature and then decreases as T ^?1 at higher temperatures. A comparison is made with the corresponding behavior of the electron-paramagnon electrical resistivity and the thermal dependence of the Lorenz number is deduced. The theory can account for the extremely large value of the thermal resistivity of plutonium and for its decrease at high temperatures.     

Influence of Ca-deficiency on the magneto-transport properties in La(0.8)Ca(0.2)MnO(3) perovskite and estimation of magnetic entropy change

La(0.8)Ca(0.2?-?x)□(x)MnO(3) (x?=?0.00, 0.10, and 0.20) perovskite was prepared by the conventional solid-state reaction and annealed at 1473?K. X-ray diffraction and scanning electron microscopy shown the existence of a secondary phase attributed to the unreacted Mn(3)O(4) oxide. The magneto transport properties have been investigated based on the temperature dependence of the resistivity ρ(T) measurements under several applied magnetic fields. We note that the La(0.8)Ca(0.2)MnO(3) (x?=?0.00) sample has a classical metal-insulator transition at T(ρ). But we have observed that the lacunars samples (x?=?0.10 and 0.20) include a metallic and insulator behavior simultaneously below T(ρ) and the resistivity is dominated by tunneling through the barriers associated with the insulating phase. In other words, the calcium deficiency favors the enhancement of the insulator behavior. The electrical resistivity is fitted with the phenomenological percolation model, which is based on the phase segregation of ferromagnetic metallic clusters and paramagnetic insulating regions. Furthermore, we found that the estimated results are in good agreement with experimental data. Above all, the resistivity dependence on the temperature and magnetic field data is used to deduce the magnetic entropy change. We have found that these magnetic entropy change values are similar to those calculated in our previous work from the magnetic measurements. Finally, we have found an excellent estimation of the magnetic entropy change based on the Landau theory.     

Electrical properties of lithium intercalated p-type GaSe

We have studied the intercalation reaction of p-type GaSe with n-butyl lithium in hexane solution through the time dependence of the electrical resistivity, and by Hall effect measurements. The electrical properties as a function of temperature have also been examined. Li_xGaSe resistivity is increasing as x is increased. The large variation of the resistivity is mainly attributed to the variation of the free carrier concentration in the host material. Lithium intercalation causes a compensation of GaSe, and the semiconducting character is conserved.     

Uniaxial pressure dependence of the Debye temperature in metals

The electrical resistance and its temperature coefficient have been measured for a platinum foil as a function of uniaxial pressure over the pressure range 0 to 60 MPa. The measurements were performed at room temperature using the transient hot-strip method. The data are analyzed using the electrical resistivity formula within the Block-Grüneisen approximation. The pressure dependence of the Debye temperature was directly obtained from an expansion of this formula and using the basic definition of the temperature resistivity coefficient. The reliability of the experimental data was then verified using the basic definition of Grüneisen constant. Within the investigated pressure range, the analysis supports the interpretation that the change in resistance of platinum under pressure is mainly due to the change in the amplitude of the atomic vibrations that are directly related to the change in Debye temperature. The pressure dependence of resistance and the Debye temperature of the platinum were reasonably good in spite of the approximations involved.     

Pressure Dependence of the Magnetic and Quadrupolar Ordering in YbRu2Ge2

We have investigated the pressure dependence of the magnetic field-temperature phase-diagram of the tetragonal compound YbRu₂Ge₂ by electrical resistivity measurements in the pressure range up to 10 GPa and for magnetic fields up to 14 T.     

Optical and electronic properties of the layered semiconductors NiPS3 and FePS3

From optical absorption data, the band-gaps for NiPS₃ and FePS₃ are found to have similar values of about 1.6 eV. A marked photoconductive effect is observed in NiPS₃, which supports this value for the energy-gap. It is confirmed by the temperature dependence of resistivity for NiPS₃, which shows intrinsic behaviour. The isostructural FePS₃ has a much lower resistivity and behaves extrinsically.     

Electrical resistivity of thin bismuth films

The thickness dependence of electrical resistivity of thin bismuth films deposited on to glass substrates has been studied in the temperature range 77 to 350 K. The structural studies show that films are polycrystalline with grain size increasing with thickness. The electrical resistivity decreases with increasing temperature. This type of temperature dependence of electrical resistivity arises due to the competition between the temperature dependences of carrier density and carrier mobility, the temperature coefficients of which are opposite in sign. The electrical properties of bismuth films are greatly affected by the presence of surface states. The size effect theory of Pichard and colleagues (PTT) has been modified to investigate the variation of charge carrier concentration with thickness. The experimental results on electrical resistivity are found to be consistent with the predictions of this modified three-dimensional model (PTT). The value of specularity parameter,p, is about 0.43 and it exhibits no temperature dependence. The experimental results on grain-boundary resistivity agree fairly well with the theoretical variations. The values of transmission coefficient,t, are determined from the experimental data.     

脉冲激光法外延生长锰氧化物薄膜

利用脉冲激光法在ＬａＡｌＯ３衬底上外延生长了Ｌａ－Ｃａ－Ｍｎ－Ｏ、Ｌａ－Ｓｒ－Ｍｎ－Ｏ等巨磁电阻薄膜,测定了这些薄膜电阻－温度特性,观测到了其铁磁转变及巨磁电阻效应,实验发现,较高的淀积温度使薄膜的峰值转变温度Ｔｐ降低,峰值电阻率增大,而高温后退火则具有相反的效果,分析比较了多种因素对薄膜生长与性能的影响及其机理。     

Resistivity measurements and the vortex phase diagram of Bi2Sr2CaCu2O y

We have measured the temperature dependence of the ab-plane resistivity on Bi₂Sr₂CaCu₂O_y single crystals with high sensitivity. A clear resistivity drop was observed when a relatively low magnetic field was applied, which is attributed to the melting transition of the flux line lattice. Three crystals with different carrier doping level were investigated and the phase diagrams are determined from the resistivity measurements. It is also shown that the phase transition temperature depends strongly on the angle between the magnetic field and the crystallographic c-axis direction, reflecting the large anisotropy of Bi₂Sr₂CaCu₂O_y.     

Measuring the temperature dependence of resistivity of high puritycopper using a solenoid coil (SRPM method)

The resistivity of high purity copper was measured by a method which estimates it by using the difference in the impedance between a circular multilayer solenoid coil with a circular rod-shaped copper sample and a similar coil without a copper sample (SRPM method). The residual resistivity ratio (RRR) of high purity copper measured at 100 Hz by the SRPM method has correlated well with the values measured by the DC four-probe method. It was confirmed that an accurate measurement of the resistivity to 10^-12 Ωm is possible by the SRPM method. Frequency dependence was confirmed to exist in high purity copper with very low resistivity. As the measuring frequency is raised, the decrease in skin depth seems to affect the resistivity     

Effect of annealing on the conductivity of electroless deposited Ni nanowires and films

We examined the effect of annealing on the conductivity of electroless deposited nickel nanowires and nanofilms. The electroless deposited nanowires were 50-200-nm thick and a few micrometers long. TEM analysis of the wires revealed that they have a bead-like (50 nm in size) structure. On annealing, in a nonoxidizing environment, the beads coalesced to form contiguous wires. Four-point resistance measurements of the nickel nanowires showed that annealed wires have considerably lower resistivity than nonannealed wires. In-situ resistance measurement of Ni nanofilms, during annealing, showed an exponential decay of resistance with temperature. The drop in resistance is thought to be a result of bead coalescence and grain-boundary attrition. After annealing, the resistivity showed a linear dependence on temperature, with the slope indicative of the electron-phonon interaction.     

Electrical resistivities in single crystals of TiC x and VC x

TiC _x and VC _x have wide non-stoichiometric composition ranges which come only from the carbon vacancies. High purity single crystals with controlled compositions were prepared, and their electrical resistivities at 4.2 and 298 K were measured as a function of composition. In the case of TiC _x whose carbon vacancies are disordered in the lattice, the dependence of the residual resistivity on the composition was interpreted' by applying Nordheim's rule to the vacancy scattering and by considering the change in carrier density due to the introduction of vacancies. In addition, the difference in the resistivity between 4.2 and 298 K was discussed. In the case of VC _x whose carbon vacancies are ordered, the dependence of the resistivity on the composition ranges of the ordered phases was examined in detail.     

Dépendance de fréquence de la résistance des couches minces d'aluminium dans la gamme des ondes centimétriques

The dependence of the surface resistivity of thin aluminium films on electric field at microwave frequencies has been studied. It was established that in the frequency range 7.7–37 GHz the resistivity is dependent on structure and either reveals the resonance type of variation or increases with increasing frequency. The capacitance and inductance of a square area in the Al films were determined from the experimental dependence of the resistivity on frequency. It was found that the inductance depends on the dimensions of surface crystalline grains and increases with the mean diameter of the grains. The resistivity of thin aluminium films produced during application of a d.c. field is less dependent on frequency than that of films formed under usual conditions.     

(1-x)La2/3Ca 1/3 MnO 3/xSb2O 5复合体系的电子输运和磁电阻行为

用两步法制备了（1-x）La2／3Ca1／3MnO3／xSb2O5复合样品．零场下电阻温度关系测量表明，对x〈3％范围。随Sb2O5含量增加，复合样品电阻率增大，绝缘体一金属转变温度降低；而对x〉3％范围，随Sb2O5含量增加。复合样品电阻率减小，绝缘体一金属转变温度提高．磁电阻测量表明，少量Sb2O5同La,2／3C＆1／3MnO3复合，可明显增强磁电阻效应．