Electric heating of copper conductors

After a critical discussion of the contemporary state of the art a new differential equation describing electric heating of a conductor in quiet air has been derived and its solution is given. It is assumed that the heating is only caused by a constant value current passing through the conductor. The solution found is in good agreement with the experimental data in the range of temperatures to which copper conductors are subjected in electrical engineering applications.     

Low-temperature resistance fluctuation in disordered conductors

At low temperatures the electron elastic mean free path in a disordered conductor can become much smaller than the inelastic mean free path (or more precisely the Thouless length) which in turn may be comparable with, or even larger than the sample size. In this quantum regime, the electrical resistance is dominated by the coherence effects that eventually lead to the now well-known weak or strong localization. Yet another remarkable manifestation of the quantum coherence is that it makes the resistance non-additive in series and, more importantly, non-self averaging, thus replacing the classical Ohm’s law with a quantum Ohm’s law describing statistical fluctuations. In this paper, we report on some of our recent work on the statistics of these “Sinai” fluctuations of residual resistance for one and higher space dimensions (d). In particular we show that the physics at the mobility edge may be dominated by these fluctuations. We also show that an external electric field tends to harness these fluctuations. Some observational consequences such as 1/f-noise at low temperatures are discussed. Our approach is based on invariant imbedding extended by us for this purpose.     

Electrical instability in quasi-one-dimensional charge density wave conductors

Narrow-band noise in niobium triselenide and similar substances is proposed to be a consequence of a negative differential dielectric constant which has been observed at field strengths larger than the threshold field. A small-signal theory is presented which yields the observed proportionality between frequency and charge density wave current. The calculation is independent of any model for the conduction and polarization mechanisms.     

Electrical conductivity in very anisotropic conductors and semiconductors

Summary For very anisotropic metallic and semiconducting systems it is shown that the electrical conductivity in the direction of high effective mass decreases as the number of electrons in the conduction band grows. In the other directions the conductivity behaves normally.

---

Riassunto Si mostra che, per sistemi semiconduttori e metallici anisotropi, la conduttività elettrica nella direzione di massa altamente efficace diminuisce all'aumentare del numero di elettroni nella banda di conduzione. Nelle altre direzioni la conduttività si comporta normalmente.

---

Резюме Для очень анизотропных металлических и полупроводниковых систем показывается, что электропропроводность в направлении большой эффективной массы уменьшается, когда число электронов в зоне проводимости увеличивается. В других направлениях проводимость ведет себя нормальным образом.

     

Isotropic graphite melting under pulsed heating

Experiments on pulsed heating (few microseconds) of graphite with measurements of the liquid carbon resistivity are described. It is confirmed that heating in water at atmospheric pressure do not allow production and study of liquid carbon; in the best case, the liquid state region beginning is achieved. Heating in sapphire tubes results in pulsed pressure (to ten of kbar) as expanding graphite bears against the tube wall. This increasing (during few microseconds) pressure makes it possible to study the carbon liquid state in a limited volume. Isochoric heating resulted in the possibilities ofmeasuring the liquid carbon resistivity at high specific energies (to ～32 kJ/g) and high pressures. Such measurements are extremely expensive at stationary studies.     

Far-infrared and millimeter wave spectroscopy of superionic copper conductors

Far-infrared and millimeter wave spectra of copper ion conducting crystal RbCu₄Cl_3+xI_2−x, which has the same structure as the room temperature silver ion conductor RbAg₄I₅, were investigated. Broad absorption peaks observed around 40, 80, and 110–200 cm⁻¹ at room temperature show doublet structures at low temperature; this may be attributed to the difference of local structure by chlorine and iodine ion. The 110–200 cm⁻¹ bands seem to be symmetric breathing modes of CuX₄ (X = Cl or I) tetrahedron and the frequency shift coincides with the square root of the mass ratio of conduction ions. The 80 cm⁻¹ band seems to be Rb-X vibration in RbX₆ octahedron. The 40 cm⁻¹ band seems to be the attempt mode which is an outward motion of the mobile ion in halogen cage. The increase of the absorption intensity at the low energy side with temperature corresponds to an increase of the DC conductivity. Plasmon fitting in energy loss function spectra was attempted.     

Skin effect in massive conductors used in pulsed electrical devices: I. Electromagnetic field of massive conductors

The diffusion of a pulsed electromagnetic field into massive conductors with an arbitrary smooth surface is considered for the case where the field penetration depth is small. By using the boundary layer method, an asymptotic solution for the electromagnetic field is constructed. First-and second-order corrections to the limiting solution, which corresponds to the field distribution at an indefinitely high conductivity of the conductors, are found. Time dependences of the first-and second-order approximations to the electric field on the surface of the conductor are determined.     

Electrical characteristics of pulsed glow discharges

The i-v characteristics, energy partitioning, and time evolution of the discharge current and reduced field (E/N) for a nitrogen discharge are simulated using a self-consistent calculation of the electron energy distribution function and the vibrational level populations. The model includes diffusion losses and takes account of the external circuit parameters. The results discussed are for pressures of 1-100 torr, discharge currents in the range of 10^-3-5.0 A, and a reduced field (E/N) in the range of 150-250 Td. For a typical discharge in a tube of 2-cm diam. and a current of a few amperes, the results show that the energy stored in the vibrational manifold saturates a few milliseconds after the initiation of the discharge     

Skin effect in massive conductors used in pulsed electrical devices: II. Massive conductors in electric circuits

Approximate relationships between the current and voltage drop across a set of massive conductors are established. They include two constant parameters: external inductance L of the conductors and skin parameter S. Specific shapes of the voltage across the massive conductors are illustrated with oscillograms. Mathematical processing of current and voltage oscillograms to estimate L and S is developed.     

Thermoelastic wave induced by pulsed laser heating

In this work, a generalized solution for the thermoelastic plane wave in a semi-infinite solid induced by pulsed laser heating is developed. The solution takes into account the non-Fourier effect in heat conduction and the coupling effect between temperature and strain rate, which play significant roles in ultrashort pulsed laser heating. Based on this solution, calculations are conducted to study stress waves induced by nano-, pico-, and femtosecond laser pulses. It is found that with the same maximum surface temperature increase, a shorter pulsed laser induces a much stronger stress wave. The non-Fourier effect causes a higher surface temperature increase, but a weaker stress wave. Also, for the first time, it is found that a second stress wave is formed and propagates with the same speed as the thermal wave. The surface displacement accompanying thermal expansion shows a substantial time delay to the femtosecond laser pulse. On the contrary, surface displacement and heating occur simultaneously in nano- and picosecond laser heating. In femtosecond laser heating, results show that the coupling effect strongly attenuates the stress wave and extends the duration of the stress wave. This may explain the minimal damage in ultrashort laser materials processing. Received: 23 May 2000 / Accepted: 26 May 2000 / Published online: 20 September 2000     

Second harmonic wave generation from Joule heating in layered organic conductors

The amplitude of a second harmonic wave (SHW) generated from Joule heating as a heat source in organic conductor β-(BEDT-TTF)₂IBr₂ is analyzed as a function of the magnetic field strength and its orientation with respect to the plane of the layers. Angular oscillations of the SHW amplitude are correlated with the angular changes of in-plane conductivity that arise from the periodic dependence of charge carriers velocity on the field orientation. It was found that the nonlinear effect of wave generation leads to a shift between the position of the peaks of the wave amplitude and in-plane conductivity. This allows an important information on the parameter values of organic conductors as well as wave velocity to be obtained. Magnetic field dependence shows that the wave is not strongly attenuated with increasing field and might give insights on the interactions between the electromagnetic, temperature and acoustic oscillations. We found that these observations are completely different compared to those of linear acoustic wave generation. It has been shown that the necessary conditions for observing the nonlinear acoustic wave generation are fulfilled in a wide range of fields and angles that allow the acoustic properties of organic conductors to be studied in detail.     

Positive and negative differential resistance in electrical conductors

A phase transition from one conducting state to another and the appearance of positive and negative differential resistance in the current-voltage characteristic is investigated experimentally for the gap instability in nonequilibrium superconductors and the avalanche breakdown in extrinsic semiconductors. Additional observation of spatial current structures in the transition regime of both solid-state systems stimulates a simple model approach connecting these spatial patterns to the measured current-voltage characteristics. Based on the underlying experimental situations considered, our model is extended to the framework of four substantial cases.     

Electrical conduction in copper vanadate

A.C. and d.c. electrical conductivities, thermoelectric power and dielectric constant of copper vanadate (CuV₂O₆) have been measured in the temperature range 300–1000 K in order to discuss the electrical conduction in the compound. The extrinsic conduction, which takes place below 500 K, has been explained by small polaron hopping mechanism while intrinsic conduction, which takes place above 500 K, has been explained by large polaron band mechanism in view of the values of activation energy and charge carrier mobility in the temperature ranges 300–500 K and 500–1000 K.     

Thermoelectric temperature measurements in laser pulsed heating of metals

Measurements of temperature pulses following focused laser irradiation on metals were performed with a specially designed thermocouple. This detector had a hot junction of an average of 5 μ in size and a rise time of less than 1 μsec. Experimental results are compared to thermal-model predictions calculated numerically. Thermal responses were also measured for laser intensities above the damage threshold of the material, in close vicinity of the damaged area. This demonstrates possible applications of the experimental technique to the investigation of damage mechanisms.     

Electrical resistivity of cyclically deformed copper

The change of the electrical resistivity of copper cyclically deformed in torsion at room temperature and in liquid nitrogen was measured. The fatigue life, hardening and the increments of resistivity of specimens deformed at the two temperatures differed appreciably. The increments of resistivity as a function of the number of cycles indicated saturation.Isochronal annealing made it possible to separate the contribution of point defects and of dislocations to resistivity. Using transmission electron microscopy the dislocation structure was found inhomogeneous. The average number of point defects and dislocations in fatigued specimens was evaluated.The author wishes to express his gratitude to M. Klesnil for his suggestion to undertake this investigation, his interest and helpful discussions. He is also indebted to Dr. P. Luká for preparing the electron micrographs and for useful discussions.     

Substrate heating effects on the propagation dynamics of laser produced plume during pulsed laser deposition of oxides

We report on the expansion dynamics of laser-produced plasma plumes of complex oxides in an oxygen atmosphere. In particular, we have studied the combined effects of background gas pressure and substrate heating on the plume propagation in typical pressure and temperature regimes of oxides thin film deposition by pulsed laser deposition. Our results evidence a reduced resistance of the background gas to the plume propagation as the substrate temperature increases. The experimental data are analyzed in the frame of a model describing the plume propagation into the background gas. Our experimental findings clearly indicate that the deposition temperature might influence film growth, not only through its direct thermal effect on the surface kinetics of adatoms, but also by affecting the energetic properties of the precursors in the gas phase.     

Recording of pulsed electromagnetic radiation in the radio-frequency range during the heating of periclase and technical glass

Schemes are given for recording the electromagnetic radiation emitted over a wide radio-frequency range (0.15–30 MHz) by dielectrics when heated with no voltage applied to the specimen and in a constant electric field. As examples, the paper describes the results of studies of pulsed electromagnetic radiation during the heating of specimens of periclase and technical glass, without any voltage being applied to the specimen and in a constant electric field, from liquid-nitrogen temperatures to 1000°C. An amplitude-frequency analysis is made of the radio pulses.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 124–131, April, 1977.