Anomalous Increase In Resistivity Research Articles

The temperature dependence of the electrical resistivity of Al-Zn alloy thin films

The electrical resistivity of vacuum evaporated A1–40 wt. % Zn thin films was found to decrease as thickness increased, thus exhibiting a size effect. Isothermal annealing of the quenched samples started with an anomalous resistivity increase to maxima followed by a normal decrease to limiting values. In the Guinier-Preston zone temperature range a measurable difference in resistivity was affected by the annealing temperature which is not the case of the bulk material. The role played by the quenched-in vacancies, grain boundary migration, phonons and the state of the solute atoms were used to explain the observed resistivity variations which were found to consist with the expected state of the alloy at the different testing temperatures. The irregularities of the position and magnitude of the observed maxima were explained in terms of the attenuation of the incident electron wave within the film as a multiple scattering effect. The observed anomalies in the resistivity during annealing were attributed to phase transformation and atomic ordering.

A resistance anomaly in a mesoscopic Al loop near the superconducting transition

We have observed an anomalous resistance increase in a mesoscopic Al loop near the superconducting transition temperature of the line and interpreted it by assuming a normal-current path in parallel with a normal-superconductor-normal quasi-particle tunnel barrier forming at the node area of the dangling voltage probes. The model gives quantitative fits to the dependence of the anomaly on various external parameters.

Anomalous interface resistance of low temperature sputtered Au/In bilayers

Au/In and In/Au bilayers are prepared at T = 86 K by ion beam sputtering and the corresponding electrical resistances are monitored in situ during film growth. For both preparation sequences (gold on a thick indium film and vice versa) an anomalous resistance increase is observed for thin top layers (1.5 nm off gold and 1.1 nm of indium respectively.) For larger thickness d, the expected 1/d behaviour is found. The above resistance increase can be consistently described by the formation of a thin amorphous interface layer of the nominal composition AuIn2 in the case of gold on top of indium and AuIn in the case of indium on top of gold. Heat treatments of In/Au multilayers (layer thicknesses dIn = 8.4 nm and dAu= 2.7 nm) prepared at 86 K lead to an interdiffusion starting at approximately 170 K and the formation of the crystalline AuIn2 phase. A thermally driven amorphization of In/Au multilayers (with modulation lengths above 6 nm) can definitely be excluded.

Electrical properties of room temperature fluorine-intercalated graphite fibers

Fluorine-intercalated graphite fibers have been synthesized at room temperature by direct reaction with elemental fluorine. The host materials were either vapor-grown fibers or pitch-based fibers. The C x F compounds obtained were mostly of the stage-3 type with a 12.65 Å repeat distance. The carbon-to-fluorine atomic ratio ranged from 10 to 14. Resistivity measurements carried out between 4.2 and 300 K show clearly that the fluorination reduces the resistivity values, whatever the type of pristine material. For fluorine-intercalated pitch-based fibers an anomalous increase of resistivity below 30 K may be consistent with a weak electronic localization or with two-dimensional carrier-carrier interaction effects. In fluorine-intercalated vapor-grown fibers the anomalous bump observed around 190 K could result from a phase transition. The room temperature value of the conductivity of this type of material, i.e. σ = 1.6 × 10 5 S cm −1, is one of the highest ever observed for fluorine-intercalated C x F fibers.

Rhodium‐catalysed reduction of vanadium pentoxide and tungsten trioxide by hydrogen

AbstractHydrogen reduction of V2O5 and WO3 catalysed by rhodium, both in the pure form and supported on kieselguhr, has been studied. The products obtained at 300°C have been identified as VO2 and HxWO3. In situ electrical resistivity measurements on V2O5 pellets, both pure and admixed with the catalyst, show an anomalous resistance increase with temperature, perhaps arising from chemisorption and spillover of hydrogen from rhodium.

Anomalous Resistivity Change in B Doped Polycrystalline Si Caused by BN Formation under N2 Heat-Treatment

B doped Si films were obtained by thermal decomposition of SiH4-BCl3-H2 gas mixture at 550°C onto thermally grown SiO2 and were heat-treated in N2 or Ar at 1100°C. The B doped polycrystalline Si exhibits an anomalous increase in resistivity for N2 heat-treatment. IMA, AES, EM and IR measurements reveal that the resistivity increase is due to decrease in B concentration in polycrystalline Si, which is caused by BN formation near the polycrystalline Si surface. The decrease rate of B concentration in polycrystalline Si and BN formation rate were measured and it is concluded that BN formation rate is determined by B and N reaction velocity.

The Microstructure of a Permalloy in the K State

AbstractThe microstructure of a 2.4 at.-% molybdenum permalloy annealed to produce the K state was investigated on the atomic scale by field-ion microscopy.It was found that the matrix is well ordered, possessing theL12 superlattice Ni3Fe, and the molybdenum atoms exhibit a tendency towards clustering.In addition the sparse heterogenous precipitation of a phase which probably contains nickel and iron, in addition to molybdenum, was observed. No microstructural inhomogeneity was observed which could account for the anomalous resistivity increase characteristic of the K state and it is therefore concluded that the changes in the electronic band structure which take place on annealing are such as to decrease the concentration offree carrier electrons.

Strong Ion Heating in a Magnetic Neutral Point Discharge

An experiment is performed to study the magnetic energy dissipation and ion heating in a magnetic neutral point discharge which is related to both an explosive energy dissipation in space plasma phenomena and the ion heating in thermonuclear fusion research.A plasma current sheet is created by exciting a plasma current along the magnetic neutral line of a two dimensional quadrupole magnetic field. A sudden anomalous increase of resistivity is observed which results in fast energy dissipation and strong plasma heating. The sudden increase of the plasma resistivity appears earlier and its magnitude increases as, i) the plasma density is decreased, ii) the discharge plasma current is increased or iii) the external quadrupole magnetic field is increased. When the sharp rise of the resistivity appears, the electron and ion temperatures rise abruptly up to several keV range Within 0.5μsec and about 10% of the initial energy Stored in the capacitor (for the plasma current excitation) is converted into ion thermal energy. This strong and efficient ion heating cannot be explained by a simple classical process and the role of turbulent waves should be important.

On the Surface Structure of the La-Doped BaTiO3-Bi2O3 Composite Ceramic Showing a Two-Step Anomalous Increase of Resistivity

A band model for the La-doped BaTi3-Bi2O3 composite ceramic which exhibits a two-step anomalous increase in resistivity with increasing temperature is tentatively proposed. The surface barrier layer built up between the semiconducting ceramic body and a silver electrode is made up of Bi2O3 and the semiconductor's surface depletion layer, and gives rise to the first anomaly around room temperature. The current-voltage characteristics with asymmetric electrodes (an In-Sn alloy applied on one side and Ag on the other side of the specimen) demonstrate that the surface barrier layer limits the current through the ceramic body below the Curie point. The width of the surface insulating layer of Bi2O3 is considered to be 10-6–10-5 cm, taking a value of 3–5 as the optical dielectric constant of Bi2O3. Capacitance-voltage characteristics around room temperature suggest that the diffusion potential and the width of the depletion layer extending from the surface to the inside of the semiconducting BaTiO3 ceramic are estimated as about 1.3 eV and of the order of 10-4 cm, respectively.

Static displacements and the electrical resistivity of interstitial alloys

It appears that the predominant mechanism by which interstitial solute atoms influence the electrical resistivity of alloys, unlike substitutional solutes, is through the associated static displacements of the host atoms. A quantitative test of this hypothesis is possible in the case of tetragonal iron-carbon martensites, where the magnitude of the static displacements is experimentally known. The resistivity component arising from the static displacements is estimated by analogy to the mean-square thermal displacements and corresponding electrical resistivity of pure iron. The result agrees fairly well with various measurements on the effect of dissolved carbon on the resistivity of martensitic alloys. The displacement hypothesis also provides a logical explanation for the anomalous resistivity increase observed during the aging of iron-carbon and iron-nickel-carbon martensites. Spontaneous rearrangements of the interstitial atoms during aging tend to occur in such a manner as to increase the static displacements, as illustrated by theoretical treatment of the formation of carbon-atom pairs. The normal aging behavior can be altered, however, by the prior introduction of a dense dislocation substructure through thermomechanical treatment, as in ausformed martensites.

Electrical Properties of Composite Ceramics with Texture Modified II

La-doped BaTiO3-Bi2O3 composite ceramics prepared by a soaking method (sintered bodies of La-doped BaTiO3 being dipped into an alcoholic solution of BiCl3 for several days, then fired to give rise to Bi2O3 matrix along the grain boundaries) exhibit a two-step anomalous increase of resistivity around room temperature and above the Curie point, when non-ohmic contact electrodes such as Ag are applied. A surface barrier-layer built in the interface between the non-ohmic electrode and the sintered body with a modified texture gives rise to an anomaly not only in the resistivity-temperature characteristic but also in the capacitance (C)-voltage (V) characteristic.The plots of 1/C2 vs. V deduced from the C-V characteristics under reverse bias to the surface barrier suggest a constant value of ca. 1.3V for the built-in voltage in the temperature range between room temperature and 58°C (at 1kHz) and in the frequency range between 0.5 and 30kHz (at 1°C). Each straight line in the 1/C2 vs. V plot reaches the maximum at the critical reverse bias, which shifts to higher voltages with temperature and frequency. It is demonstrated that the type of the surface barrier-layer is the one of modified MOS type.

Two-Step Anomalous Increase of Resistivity on La-Doped BaTiO3-Bi2O3 Composite Ceramics with Surface Barrier-Layer

Two-step anomalous increase of resistivity is observed on La-doped BaTiO3–Bi2O3 composite ceramics with glazed silver paste as electrodes, where the first increase appears around a room temperature and the second above the Curie temperature. On the other hand, when indium-base alloy electrodes are used to obtain ohmic contacts, the former disappears and the latter diminishes. The existence of barrier-layers between opposing electrodes and pellet surfaces is demonstrated by resistivity measurements using asymmetric electrodes. It seems that Bi2O3 forms a barrier-layer.

Resistance Changes in Iron-Base Alloys Forming Ni3(AI Ti) Precipitates

The resistivity of Fe-Ni-Cr solid solutions increases and the temperature coefficient decreases with rise in nickel content. This explains the peculiarity observed in γ′-forming stainless steels of a resistance increase on ageing that is greater when measured at the ageing temperature than at a low temperature. A range of steels with varying Ni content and Ti/Al ratio has been examined and the anomalous resistivity increase calculated. This is shown to be independent of temperature within the accuracy of the experiments and to decrease slowly with increase in γ′ size, but some effect remains at particle sizes of 25–30 nm dia. Cold work lowers the resistivity of Fe-Ni-Cr alloys with high Ni content and a rapid increase occurs on annealing at 500°C (773 K). A similar effect is observed in the high-nickel γ′ - forming alloys and is thought to be due to short-range order in the matrix.

Experimental Study of Magnetic Flux Transfer at the Hyperbolic Neutral Point

A laboratory study is reported herein of a plasma flow process sometimes referred to as the severing and reconnecting of magnetic field lines at a hyperbolic or X-type neutral point. It is found that a hyperbolic pinch develops at the neutral point resulting in plasma compression. The Ohmic electric field of the pinch current enables field line reconnection to take place through resistive diffusion. The reconnection rate is substantially increased by a reduction in the size of the pinch region effected by flow adjustment through pairs of stationary slow mode shocks in a manner similar to that deduced and described by Petschek. Strong evidence is presented for this wave-dominated configuration. However, it is found that the pinch current becomes progressively concentrated at the neutral point and along the shock loci until eventually a critical current density is reached marked by a sudden and large anomalous increase in resistivity as predicted by Friedman and Hamberger. At this point the wave-assisted diffusion mode is terminated and there is observed: (1) a cutoff in pinch current, (2) a large increase in the electric field, (3) corresponding increase in reconnection rate, and (4) generation of a system of large amplitude fast-mode waves. The waves, bearing evidence of the onset of plasma turbulence, effect a rapid and gross redistribution of flux among the cells defined by the separatrix, and blow the slow mode shocks off downstream. The increased electric field raises the possibility of rapid magnetic energy dissipation through acceleration of particles to high energy.

The anomalous increase in resistivity of nickel on annealing at high temperatures

The anomalous increase in resistivity of nickel on annealing at high temperatures

Calculations on the resistivity of alloys during pre-precipitation

The residual resistivities of various binary alloys, during the early stages of G.P. zone formation, are calculated using free electron transport. It is shown that Bragg scattering, due to the microstructure of the zones, leads to the observed anomalous increase in resistivity.

Resistivity Anomaly in Doped Barium Titanate

The barrier‐layer model previously proposed to explain the anomalous increase in resistivity that occurs in doped BaTiO3 has been reexamined in the light of data obtained from more recent experiments. The picture thus obtained describes correctly and quantitatively the resistivity anomaly and the frequency and voltage dependence of the resistivity in the entire temperature range investigated (‐180° to +200°C). The activation energy of the donors and of the surface states as well as the density of states in BaTiO3 were determined and are in close agreement with other investigations. Comments are made regarding the uncertainty of the nature of the surface states.

Resistivity Changes due to Formation of G. P. Zones (Clusters rich in Solute)

AN anomalous increase in resistivity has been observed during formation of G. P. zones (clusters rich in solute) in several aluminium alloys1,2. Mott3 suggested that this effect may be due to a critical scattering of the conduction electrons when the zone grows to dimensions of the wave-length of the conduction electrons. Matyas4 showed on theoretical grounds that a maximum should occur for the resistivity change during zone formation.

Temperature-Dependence of the Electrical Resistivity of bcc Cr–Fe Alloys

The electrical resistivity vs temperature was determined for a bcc Cr+20 at.% Fe alloy from 4.2° to 300°K. The absence of any discontinuity in this curve indicates that the very high temperature-coefficient of the linear term of the specific heat previously found at that composition is not associated with a phase transformation between room temperature and 4.2°K. For bcc Cr-alloys with Fe contents increasing from 0 to 16 at.% Fe the resistivity vs temperature anomaly shifts from approximately 308°K to progressively lower temperatures, and the anomalous resistivity increase with decreasing temperature becomes progressively larger. It is quite possible that these anomalies are connected with antiferromagnetic-paramagnetic transition in the alloys considered.

Anomalous increase of resistivity during ageing of aluminium-silver alloys

Anomalous increase of resistivity during ageing of aluminium-silver alloys