Temperature Coefficient Of The Resistivity Research Articles

Athermal ω Phase and Lattice Modulation in Binary Zr-Nb Alloys.

To further explore the potential of Zr-based alloys as a biomaterial that will not interfere with magnetic resonance imaging (MRI), the microstructural characteristics of Zr-xat.% Nb alloys (10 ≤ x ≤ 18), particularly the athermal ω phase and lattice modulation, were investigated by conducting electrical resistivity and magnetic susceptibility measurements and transmission electron microscopy observations. The 10 Nb alloy and 12 Nb alloys had a positive temperature coefficient of electrical resistivity. The athermal ω phase existed in 10 Nb and 12 Nb alloys at room temperature. Alternatively, the 14 Nb and 18 Nb alloys had an anomalous negative temperature coefficient of the resistivity. The selected area diffraction pattern of the 14 Nb alloy revealed the co-occurrence of ω phase diffraction and diffuse satellites. These diffuse satellites were represented by gβ + q when the zone axis was [001] or [113], but not [110]. These results imply that these diffuse satellites appeared because the transverse waves consistent with the propagation and displacement vectors were q = <ζ ζ¯ 0>* for the ζ~1/2 and <110> directions. It is possible that the resistivity anomaly was caused by the formation of the athermal ω phase and transverse wave. Moreover, control of the athermal ω-phase transformation and occurrence of lattice modulation led to reduced magnetic susceptibility, superior deformation properties, and a low Young’s modulus in the Zr-Nb alloys. Thus, Zr-Nb alloys are promising MRI-compatible metallic biomaterials.

Thermoelectric and magnetic properties of Ce3Cu3−xAuxSb4 compounds

We present the result of magnetic and thermoelectric investigations of the series of Ce3Cu3−xAuxSb4 compounds. The experimentally obtained data are discussed based on ab initio band structure calculations. It has been shown that structural disorder resulting from doping of Ce3Cu3Sb4 with Au induces a spin-glass-like behavior in the Ce3Cu3−xAuxSb4 series. All components x exhibit a negative temperature coefficient of the resistivity and metallic behavior of thermopower S(T) in the temperature region of T &amp;gt; 100 K. The maximal S value of 250 μV/K was measured for the pristine Ce3Au3Sb4 sample, while the highest figure of merit ZT = 0.06 was obtained for sample x = 1.5 at the highest measured temperature (T = 390 K).

The Impact of Disorder on the Disappearance of Metamagnetic Behavior and Enhancement of Temperature Coefficient of Resistivity for (La1−xNdx)2/3(Ca1−ySry)1/3MnO3 Ceramics

The polycrystalline samples (La1−xNdx)2/3(Ca1−ySry)1/3MnO3 were prepared by the solid-state reaction method. Magnetization measurements versus temperature were performed in order to investigate the magnetic properties such as the metamagnetic transition. The transition temperature estimated from the maximum of dM/dH is found sensitive to disorder σ2 leading to the formation of an inhomogeneous metastable state and to subsequent magnetization jumps. The peak temperature coefficient of the resistivity improved significantly from 1.54 to 8.21% K−1 due to the increase in disorder. These findings suggest that (La1−xNdx)2/3(Ca1−ySry)1/3MnO3 ceramics can be used to prepare uncooled infrared bolometers.

VISCOSITY AND ELECTRICAL RESISTIVITY OF LIQUID CuNiAl, CuNiAlCo, CuNiAlCoFe ALLOYS OF EQUIATOMIC COMPOSITIONS

We measured the resistivity of liquid CuNi, CuNiAl, CuNiAlCo, CuNiAlCoFe alloys of equiatomic compositions using the rotating magnetic field method to obtain information on their liquid structures. We saw the alloys of equiatomic composition as the high-entropy alloys (HEAs). The results discussed in framework of conception a microheterogeneous structure of a metallic melt. A conclusion is made about cause of modification of temperature dependence of resistivity of liquid HEAs due this microheterogeneous structure. All the investigated melts demonstrate the change in the temperature coefficient of the resistivity for heating and cooling. It was determining the temperature T* is the temperature of the changes the microheterogeneous structure of a metallic melt. The value of temperature T* for all alloys is 1500oC .The change in the temperature coefficient of the resistivity of the melts on heating to 1500oC we interpreted using the Nagel–Tauc model.

On the extraction of resistivity and area of nanoscale interconnect lines by temperature-dependent resistance measurements

Several issues concerning the applicability of the temperature coefficient of the resistivity (TCR) method to scaled interconnect lines are discussed. The central approximation of the TCR method, i.e. the substitution of the interconnect wire TCR by the bulk TCR becomes doubtful when the resistivity of the conductor metal is strongly increased by finite size effects. Semiclassical calculations for thin films show that the TCR deviates from bulk values when the surface roughness scattering contribution to the total resistivity becomes significant with respect to grain boundary scattering, an effect that might become even more important in nanowires due to their larger surface-to-volume ration. In addition, the TCR method is redeveloped to account for line width roughness. It is shown that for rough wires, the TCR method yields the harmonic average of the cross-sectional area as well as, to first order, the accurate value of the resistivity at the extracted area. Finally, the effect of a conductive barrier or liner layer on the TCR method is discussed. It is shown that the liner or barrier parallel conductance can only be neglected when it is lower than about 5–10% of the total conductance. It is furthermore shown that neglecting the liner/barrier parallel conductance leads mainly to an overestimation of the cross-sectional area of the center conductor whereas its resistivity is less affected.

The effect of the solidification rate on the physical properties of the Sn-Zn eutectic alloy

As-cast Sn-8.8 wt.% Zn eutectic alloy was directionally solidified with a constant temperature gradient (G = 4.16 K/mm) under various solidification rates (V = 8.3–790 μm/s) in a Bridgman-type furnace. The dependence of the microhardness (HV), ultimate tensile strength (σut), ultimate compressive strength (σuc), and compressive yield strength (σcy) on the solidification rate was determined. The temperature dependency of the electrical resistivity (ρ) of the sample was investigated, and the temperature coefficient of the resistivity (α) was calculated from ρ−Τ curve. The specific heat (CP) and the enthalpy (ΔH) were determined by DSC analysis. The thermal conductivity was calculated using the Wiedemann-Franz equation.

EFFECT OF HEAT TREATMENT CONDITIONS ON ELECTRICAL RESISTIVITY OF 35KhGF MOLTEN STEEL

The authors have studied the effect of the grain structure, crystal structure and defects of 35KhGF steel samples on the character of temperature dependence of the melt specific electrical resistance at temperatures of 1450–1720 °C. Grain and crystalline structures changed as a result of heat treatment - normalization and tempering. The peculiarities of grain and crystalline structures, the defects were recognized according to the results of metallographic study. The metallographic study was carried out by diffraction of backscattered electrons-EBSD analysis. Scanning areas were chosen with the inclusion of defects in metal of technological origin, namely, microscopic discontinuities filled with gas or slag. The results of EBSD analysis are drawn as IPFpatterns; they show the texture state of the samples using the color assignment method. The microstructure of a 35KhGF steel sample after normalization at 910 °C has the smallest crystallites (of the order of 1 μm) and the largest extent of the grain boundaries. All samples have defects – discontinuities of the order of 1 μm in size. Specific electrical resistance of molten 35KhGF steel samples was measured by the method of rotating magnetic field in heating mode and subsequent cooling. For samples preliminarily normalized at 910 °C, a discrepancy in the temperature dependences of resistivity and an irreversible decrease in the resistivity temperature coefficient were observed in cooling mode of the melt. The discrepancy between the temperature dependences of the electrical resistivity and the irreversible decrease in the temperature coefficient of the resistivity was analyzed on the basis of the microinhomogeneous structure concepts of metallic melts and the phenomenon of metallurgical heredity. According to the notion of the microheterogeneous structure of metallic melts, the melting of a multiphase steel ingot does not immediately produce a homogeneous solution of the alloying elements in the iron at the atomic level, and a chemically microinhomogeneous state is maintained in a certain temperature range. Looking at the branching of the temperature dependences of the electrical resistivity, the transition of the melt into the state of true solution occurs only near the temperature T* = 1640 °C. The value of temperature T* according to the notion of the structural metallurgical heredity phenomenon depends on microstructure, phase composition and crystalline structure of the initial sample. The presence of discontinuities leads to appearance of an excess volume of melt during metal melting, which is partially retained during cooling and crystallization. In this case, the temperature coefficient of the resistivity in cooling mode is close to zero in absolute value, even at ingot cooling rates of the order of 10 °C/s the crystallization conditions change, in particular, the metal’s propensity to amorphization increases.

Epitaxial thin films of Dirac semimetal antiperovskite Cu3PdN

The growth and study of materials showing novel topological states of matter is one of the frontiers in condensed matter physics. Among this class of materials, the nitride antiperovskite Cu3PdN has been proposed as a new three-dimensional Dirac semimetal. However, the experimental realization of Cu3PdN and the consequent study of its electronic properties have been hindered due to the difficulty of synthesizing this material. In this study, we report fabrication and both structural and transport characterization of epitaxial Cu3PdN thin films grown on (001)-oriented SrTiO3 substrates by reactive magnetron sputtering and post-annealed in NH3 atmosphere. The structural properties of the films, investigated by x-ray diffraction and scanning transmission electron microscopy, establish single phase Cu3PdN exhibiting cube-on-cube epitaxy (001)[100]Cu3PdN||(001)[100]SrTiO3. Electrical transport measurements of as-grown samples show metallic conduction with a small temperature coefficient of the resistivity of 1.5 × 10−4 K−1 and a positive Hall coefficient. Post-annealing in NH3 results in the reduction of the electrical resistivity accompanied by the Hall coefficient sign reversal. Using a combination of chemical composition analyses and ab initio band structure calculations, we discuss the interplay between nitrogen stoichiometry and magneto-transport results in the framework of the electronic band structure of Cu3PdN. Our successful growth of thin films of antiperovskite Cu3PdN opens the path to further investigate its physical properties and their dependence on dimensionality, strain engineering, and doping.

Measurement of the electrical resistivity of liquid 32G2 and 32G1 steels by the rotating magnetic field method

The resistivity of liquid 32G2 and 32G1 steels are measured using the rotating magnetic field method to obtain information on their liquid structures. The technique of measurements is described and the influence of self-induction and viscosity on the resistivity is estimated. The results are discussed in the framework of a microheterogeneous structure of a metallic melt. A conclusion is made about the character of the influence of slag inclusions detected by magnetic powder and ultrasonic methods on the temperature dependences of the resistivities of liquid 32G2 and 32G1 steels. The change in the temperature coefficient of the resistivity of the melt on heating to 1700°C is interpreted using the Nagel–Tauc model.

γ-U phase in U-Pt system retained to low temperatures by means of rapid cooling

Splat-cooling technique with a cooling rate better than 106 K/s helps to increase the Pt solubility in the (cubic) γ-U phase and retain such γ-U phase in U-15 at.% Pt splat down to low temperatures. The splat-cooled U-Pt alloys are very stable in exposing to air. The γ-U phase (U-15 at.% Pt splat) is characterized by a negative temperature coefficient of the resistivity (dρ/dT < 0). The splats become superconducting below 1.1 K.

Silica aerogel thick film, an alternative to micromachined air gap for thermal insulation

A uniform, smooth and crack-free multilayer silica aerogel film as thick as 5 µm is successfully coated on top of a silicon wafer. The multilayer spin-coated aerogel film was made possible by using the present authors' recently developed novel state-of-the-art aerogel processing technique. The utilisation of the thick aerogel film for the thermal insulation of a microhotplate (µHP) is studied. The super heat insulator aerogel can replace the micromachined air cavity conventionally created under µHPs for the fabrication of metal oxide gas sensors. The thermal insulation capability of the unique aerogel film was investigated by measuring the temperature of the nichrome heaters built on the aerogel coated silicon wafers at different applied powers. The temperature coefficient of the resistivity of the heaters was measured by monitoring the change in the resistance of the heaters at different temperatures. Simulations were also performed using COMSOL multiphysics software for verification of the experimental results, showing good agreement.

Electrical transport properties of Ge-doped GaN nanowires

The conductivity and charge carrier concentration of single GaN nanowires (NWs) doped with different concentrations of Ge were determined by four-point resistivity and temperature-dependent Seebeck coefficient measurements. We observed high carrier concentrations ranging from 9.1 × 1018 to 5.5 × 1019 cm−3, well above the Mott density of 1.6 × 1018 cm−3, and conductivities up to 625 S cm−1 almost independent of the NW diameter. The weak temperature dependence of the conductivity between 2 and 10 K could be assigned to the formation of an impurity band. For the sample with the highest conductivity metallic behaviour was found, indicated by a positive temperature coefficient of the resistivity. The near band edge emission analyzed by micro-photoluminescence spectroscopy showed only a small increase of the peak width up to 70 meV and no spectral shift for carrier concentrations up to 5.5 × 1019 cm−3. The latter was attributed to the simultaneous influence of band filling, band gap renormalization, and strain.

Investigation of the Some Physical Properties of the Directionally Solidified Al–Cu–Co Ternary Eutectic Alloy

The Al–23.9% Cu–1.2% Co (wt%) ternary eutectic alloy was prepared using a vacuum melting furnace and a casting furnace. The samples were directionally solidified upwards at a constant growth velocity (18.8 μm/s) under different temperature gradients (1.23–5.66 K/mm) and at a constant temperature gradient (5.66 K/mm) under different growth velocities (8.3–166 μm/s) in a Bridgman-type directional solidification furnace. The dependence of the eutectic spacing on the solidification parameters (temperature gradient and growth rate) and that of the microhardness and compressive strength on the eutectic spacing and solidification parameters were investigated. The electrical resistivity measurements of the studied alloy were performed and the temperature coefficient of the resistivity was calculated from the curve of the resulting ρ–Τ plot. The thermal conductivities of the sample grown at a constant temperature gradient and growth rate were obtained using the Wiedemann–Franz and Smith–Palmer equations.

Effect of Hydrogen Absorption on Electrical Transport Properties for Ni&lt;sub&gt;36&lt;/sub&gt;Nb&lt;sub&gt;24&lt;/sub&gt;Zr&lt;sub&gt;40&lt;/sub&gt; Amorphous Alloy Ribbons

Electrical resistivity measurements in the temperature range from 6 to 300K were carried out in order to investigate the effects of the hydrogen absorption on the transport properties of Ni36Nb24Zr40 amorphous alloy ribbon. The electrical resistivity basically behaved negative temperature dependence in all prepared specimens of (Ni0.36Nb0.24Zr0.40)100¹xHx with 0 ¯ x < 15. The absolute value of temperature coefficient of the resistivity, TCR, increased with increasing the amount of the absorbed hydrogen. In addition, it was also clear that the electrical resistivity gradually increased with the time just after electrochemically charging, and tended to saturate after about 800ks at 300K. The behavior of the gradual increase in the electrical resistivity with the time was explained by the model including two kinds of the relaxation times, being associated with the migration of the hydrogen from the sample surface. [doi:10.2320/matertrans.MF201305]

Transport Properties of Ni-Nb-Zr Glassy Alloys and Hydrogen Absorbed Alloys

The electrical transport properties of (Ni0.8Nb0.2)100－xZrx (x = 30, 40 and 50) amorphous ribbons and hydrogen charged specimens were investigated. The amorphous ribbons indicated a negative coefficient in the temperature dependence of their electrical resistivity as well as the typical transport properties of the amorphous alloys with comparatively high values of electrical resistivity, ρ. The normalized temperature coefficient of the resistivity (TCR ≡ 1/ρ300K·dρ/dT) tended to increase with increasing x in the temperature range of 100-300 K. These behaviors would suggest that the transport properties of the present amorphous ribbons were governed by temperature variation of the Debye-Waller factor, not by electron-phonon scattering. The hydrogen charged ribbons obtained by an electrochemical method also showed similar electrical resistivity behaviors as a function of the temperature. However, TCR of x = 40 with hydrogen charged ribbon, in which the amount of absorbed hydrogen was about 14 at%, increased about three times more than that of the pre-charged amorphous ribbon.

Controlling the resistivity of multi-walled carbon nanotube networks by copper encapsulation

The resistivity of multi-walled carbon nanotube networks can be changed by filling Cu into the nanotubes as well as by preparing the nanotube networks with various densities. The resistivity can be controlled to be lower than the c-axis resistivity of graphite, and has a low temperature coefficient of −1.12 × 10 −5/K over the temperature range of 20–500 K. Filling Cu into the nanotubes decreases the intra-tube resistivity, but the temperature coefficient of the resistivity is governed by the inter-tube resistivity of the nanotube network.

Resistivity of Thin Films of MoSi&lt;sub&gt;2&lt;/sub&gt;–Si Composites

Thin films of the composite of molybdenum silicate (MoSi2) and silicon (Si) were fabricated by radio frequency magnetron sputtering using a target made of a powder mixture of MoSi2 and Si. The composite thin film consisted of two types of molybdenum silicate with hexagonal and unknown crystal structures. The temperature dependence of the resistivity of a thin film was measured using the four-probe method. The sign of the temperature coefficient of the resistivity changed from positive to negative with increasing molar ratio of Si to Mo. It was suggested that molybdenum silicate with the hexagonal structure had both positive and negative temperature coefficients of resistivity, whereas the unknown structure showed only a negative temperature coefficient of resistivity.

Thin tantalum films on crystalline silicon – a metallic glass

AbstractThin amorphous tantalum films are prepared on Si(111) substrates in a metallic glassy state. The amorphous monoatomic state of the film is characterized by X‐ray diffraction studies. The glassy state leads to a negative temperature coefficient of the resistivity (TCR) for low sample temperatures &lt;200 K which is attributed to incipient localization. Above 200 K a positive TCR is observed as expected for a normal Boltzmann transport regime. Upon heating the Si substrate to 1200 K TaSi2 is formed out of the amorphous tantalum film and the silicon substrate. The TaSi2 layer is crystalline as evident from X‐ray diffraction data.magnified imageSchematic drawing of the evaporation setup on either glass or silicon samples. Scheme of annealing effects.(© 2011 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Cage-Shaped Mo9 Chalcogenides: Promising Thermoelectric Materials with Significantly Low Thermal Conductivity

Thermoelectric properties of molybdenum selenides containing Mo9 clusters have been investigated between 300 K and 800 K. AgxMo9Se11 (x = 3.4 and 3.8) have been synthesized by solid-state reaction and spark plasma sintering. X-ray diffraction and scanning electron microscopy reveal high purity and good homogeneity of the samples. The thermoelectric power of the samples is positive over the whole investigated temperature range, indicating that the majority of charge carriers are holes. The Seebeck coefficient increases with temperature, and the temperature coefficient of the resistivity is positive. Significantly low thermal conductivity, comparable to values reported for state-of-the-art thermoelectric materials, is observed in this new system, and this is assumed to be associated with the rattling effect from the Ag filler atoms. It has been demonstrated that the electrical and thermal properties correlate to the Ag concentration. For x = 3.8, a promising dimensionless thermoelectric figure of merit of ∼0.7 is obtained at 800 K.

Preparation and properties of thin amorphous tantalum films formed by small e-beam evaporators

Large area (A = 6 cm2), thin tantalum films (5 nm < d < 100 nm) are accomplished by evaporation from tantalum rods using small pocket e-beam evaporators. Using a sample to source distance of ≈20 cm, homogeneous amorphous films with a small surface roughness (<1 nm) can be prepared on glass. Films are characterized by scanning electron microscope images, atomic force microscopy, electrochemical oxidation and resistivity measurements as a function of film thickness. The samples show high resistivities of 200–2000 µΩ cm. The temperature coefficient of the resistivity (TCR) is negative, as characteristic for highly disordered metals. A theoretical description of the thickness distribution (evaporation from plane and hemispherical sources on plane targets) is given in the appendix.