Crystallization-water-stimulated dynamic conductivity

In water-molecule-doped barium peroxide and barium oxide, a step increase in the dynamic conductivity to ∼10⁻³ Ω⁻¹ cm⁻¹ was found. The increase is observed when water molecules are present in two nonequivalent states in the lattice, with concentrations of the molecules n _t of ≥2.2×10²¹ cm⁻³. At n>n _t , the conductivity does not depend on the number of molecules in the lattice but is temperature-dependent, obeying the law σ(T = C ₁exp(−E ₁/kT) + C ₂exp(−E ₂/kT. The run of the σ(n, T) curve is explained by trapping electrons that result from H₂O dissociation and by two sorts of carrier jumps between localized and delocalized states.     

Green function theory of dynamic conductivity

The transport processes can be discussed either by kinetic equation method or by correlation function method. Using the former, linear transport equations are developed for the study of dynamic conductivity of a quantum imperfect gas employing a resolution of BBGKY hierarchy using Green functions. From this transport equation a modified form of Kubo (correlation function) formula is obtained to show the equivalence between the two methods. This equivalence may be used for the justification of the concept of adiabatic switching of the field. The simple formula derived, gives the conductivity in terms of one-particle Green function, unlike the usual discussions which express it in higher order Green functions.     

动态法测定良导体热导率的实验研究

对“用动态法测定良导体热导率”实验的数据处理方法进行了探索，提出两种改进方法并在实际应用中得到了较好的效果，对实验涉及到的准一维热传导方程及其波动解作了理论分析（引入了散热修正）和解释。     

Diffusion of hydrogen and oxygen in the high temperature proton conductor srceo3 investigated by dynamic conductivity measurements

In SrCeO₃ the oxygen vacancy concentration at elevated temperatures depends on the oxygen partial pressure in the surrounding atmosphere. Changes of the oxygen vacancy concentration are accompanied by change in the hole concentration and therefore can be measured by electrical conductivity measurements. We apply a dynamic method for studying the diffusion of oxygen vacancies by measurements of the time dependence of the electrical conduction after a sudden change in the oxygen partial pressure has taken place.

In doped samples and under wet conditions the protonic charge carriers are mainly incorporated by a dissociative absorption of water and lead to a noticeable protonic conduction. The proton diffusion in SrCe_0.95 Y_0.05O₃ is determined by relaxation measurements at a polarised sample in wet and hydrogen containing atmosphere. The electrochemical cell discussed here is characterised by a combination of one reversible and one (hydrogen) ion blocking electrode. From the time dependence of the depolarisation process the hydrogen diffusivity is extracted.     

Raman spectroscopy and low temperature electrical conductivity study of thermally evaporated CdS thin films

A systematic study has been carried out on properties of CdS thin films grown on glass substrates by thermal route and growth parameters have been optimized to achieve near stoichiometry. Raman spectroscopy of the films has been carried out to get more insight on chemical and structural information of the films. Photoluminescence study was carried out to get the knowledge of defect-states which play major role in transport mechanisms. In order to obtain electrical parameters, Hall measurement has been carried out by van der Pauw’s technique at room temperature. Also, variation of electrical resistivity of the films at temperature range 20–300 K has been studied. Finally effect of post deposition annealing on the structural, optical and electrical properties of these films has been studied.     

Negative high-harmonic dynamic conductivity in a superlattice

In this paper, we discuss high-frequency generation in a semiconductor superlattice (SL). In particular, we have studied the diffusive regime where Bloch oscillations and electrical domains do not develop and generation may occur as a result of the negative high-harmonic non-linear conductivity. We underline the difference between this regime and frequency conversion in a stable non-linear medium: for high-harmonic instability to occur, thresholds in ac and dc driving forces must be reached. We point to AlGaN/GaN as a possible material system for high-power SL terahertz sources.     

Remarkable power-law temperature dependencies of inter-grain conductivity

Electrical conductivities with temperature dependencies of the type σ(T)−σ(0)∝T^p are remarkable when measurements over extended ranges of T show that p=1 or 2 over wide ranges of σ. We report on such behaviors for inter-grain conductivities of polycrystalline Sr₂CrMoO₆ samples. We show that for certain ranges of parameters the ‘fluctuation induced tunneling’ model fits these dependencies very well.     

Low temperature conductivity of carbon nanotube aggregates

We compare, over wide temperature ranges, the transport properties of single-wall carbon nanotubes arranged in the form of aligned arrays or in the form of fibres. The experimental data show that both the forms of aggregates present a crossover in the transport mechanism from three-dimensional hopping of the electrons between localized states at high temperature to fluctuation-induced tunnelling across potential barriers at low temperature. The role of the junctions formed between the bundles in the array and between the nanotubes inside the fibres is discussed on the basis of the experimental results.     

Pyroelectric properties of lithium triborate in the temperature range from 4.2 to 300 K

Temperature dependences of pyroelectric coefficients γ^T and γ^S corresponding to the mechanically free (T) and clamped (S) states of a lithium triborate (LBO) sample are studied and found to be nonmonotonic. It is proposed that the anomalies are associated with an increase in anharmonism of the lithium sublattice of LBO long before its transition to the superionic state. The spontaneous polarization at T=200 K is estimated to be 0.25 C/m². In the structural motif, the mesotetrahedra responsible for the emergence of spontaneous polarization of LBO are singled out.     

On the dynamic conductivity for an electron-impurity system

The correlation function formula for the dynamic conductivity of a system of non-interacting electrons in the field of impurities is analyzed in terms of proper connected diagrams. By selecting those diagrams appropriate in the region of weak coupling and low impurity concentration, a set of coupled equations for the energy broadening γ (ω, ε, n_s) and the energy shift Δ(ω, ε, n_s) is derived, where both γ and Δ depend on the frequency ω of a probing field, the energy ε of the electron, and the concentration, n_g, of impurities. With the assumption of a finite range potential, these equations are solved. It is found that γ (ω, n_s) is smaller than that extrapolated value which the conventional expression γ₀ for the low-concentration collision frequency would predict, in the entire region studied, that the difference γ₀-γ becomes appreciable when the ratio of the average time between scatterings, τ_c, to the average duration of a scattering, τ_d, is 100 or less, that γ (ω, n_s) decreases monotonically from its static value γ (0, n_s), and becomes vanishingly small in the region ω≈1/τ_d, and that in the static limit (ω=0), γ=γ₀[1?(2/π) (γ₀τ_d)+…], that the energy shift Δ is positive, and increases from 0 and reach a peak of magnitude γ₀ as ω is raised from 0. By using the γ and Δ obtained, the dynamic conductivity σ(ω, n_s) for degenerated electrons is calculated. The deviation, σ-σ₀, from the conventional expression σ₀=(?i) (n_ee²/M) [ω-iΓ₀]^?1, (n_e]=number density of electrons), for 0°K, is appreciable when the ratio τ_c/τ_d is 100 or less. The field-term correction, which arises from the modification of the scattering due to the probing field, is found to be negligible in the entire region studied.     

Electrical conductivity at high temperature and thermodynamic study of point defects in single crystalline cuprous oxide

In order to follow the variation of point defect interactions in relatively concentrated solutions we have studied the electrical conductivity of cuprous oxide in the range of temperature 650–1100°C and for oxygen partial pressures greater than 10^?6 atm. The P^{$\text{1}\text{π}$}_O2 dependence of the conductivity varied non linearly from about n = 8 for P_o2 close to 10^?6 atm. to lower values of n with increasing oxygen partial pressure. The activation enthalpy of conductivity determined in these ranges of temperature and oxygen partial pressure has been found to be also a function of temperature and varied between 12 and 17 kcal mol^?1.The interpretation of these results has permitted us to show that the departure from linearity of the plots of log or log $\text{σ = ?(}\text{l}\text{T}\text{)}$ excludes the existence of an ideal solution of ionized and non-ionized copper vacancies as was proposed previously in the literature. To explain these results it is possible to take into account a partially disordered distribution of these defects. It is shown that the increase of interactions and consequently the variation of the electrical conductivity as a function of the thermodynamic parameters, may be simulated by an ideal solution including new charged species of the type (V'_CuV^x_Cu).     

材料变温电导测量系统

针对合金材料在温度变化过程中电导率的变化引起性能改变问题,为此,设计了一套材料电导率测量系统.通过简单的操作就能测量从常温到低温下的材料电导率,并实现数据的显示、保存、打印和网络传输等功能.该系统利用温度校正方法,消除了温度变化给电导率引起的测量误差.该系统具有较高的测量精度,可广泛应用于不同材料的电导率测量.     

Low temperature lattice conductivity of some two-dimensional magnetic crystals

The low temperature lattice conductivity of the two-dimensional Heisenberg ferromagnets (C_nH_2n+1NH₃)₂CuCl₄, n = 1, 2 have been measured in high magnetic fields up to 6.5T. From these measurements information is obtained about the dimensionality of the acoustical phonon spectrum. An estimate of the phonons mean free path and of the dislocation density of the crystals is made.     

Electrical conductivity of nonideal hydrogen plasma at megabar dynamic pressures

The electrical conductivity of a nonideal hydrogen plasma is measured under shock-wave compression to pressures ∼1.5 Mbar. It is found that the conductivity increases sharply (by five orders of magnitude) at a density ρ∼0.3−0.4 g/cm³, reaching close to liquid-metal values ∼10³ S/cm. The data obtained can be described by a nonideal-plasma model taking into account the increase in the number of conduction electrons as a result of “ionization by pressure.” Pis’ma Zh. éksp. Teor. Fiz. 69, No. 12, 874–878 (25 June 1999)     

Pyroelectric properties of polyethylene oxide

Physics of the Solid State - Transformations of the structure and changes in the polarization properties of polyethylene oxide are investigated in the crystallization region. It is demonstrated...     

温度传感器在测定不良导体导热系数实验中的应用

将单片计算机与温度传感器结合用于导热系数测定仪中测量温度,改进后的导热系数测定仪结构紧凑,操作简单、读数方便.     

Logarithmic temperature dependence of the conductivity of the two-dimensional metal

We report on the first observation and studies of a weak delocalizing logarithmic temperature dependence of the conductivity, which causes the conductivity of the 2D metal to increase as T decreases down to 16 mK. The prefactor of the logarithmic dependence is found to decrease gradually with density, to vanish at a critical density n _c , 2∼2×10¹² cm⁻², and then to have the opposite sign at n>n _c ,2. The second critical density sets the upper limit on the existence region of the 2D metal, whereas the conductivity at the critical point, G _c ,2∼120e ²/h, sets an upper (low-temperature) limit on its conductivity. Pis’ma Zh. éksp. Teor. Fiz. 68, No. 6, 497–501 (25 September 1998) Published in English in the original Russian journal. Edited by Steve Torstveit.     

Casimir force at both nonzero temperature and finite conductivity

We find the combined effect of nonzero temperature and finite conductivity onto the Casimir force between real metals. Configurations of two parallel plates and a sphere (lens) above a plate are considered. Perturbation theory in two parameters (the relative temperature and the relative penetration depth of zero-point oscillations into the metal) is developed. Perturbative results are compared with computations. Recent improper computations based on the Lifshitz formula for the temperature Casimir force are discussed.     

Thermal conductivity of hcp iron at high pressure and temperature

Results of steady-state heat transfer experiments on iron in laser-heated diamond anvil cell, combined with numerical simulation using finite-element method are reported. Thermal boundary conditions, dimensions of sample assemblage, heating-laser beam characteristics and relevant optical properties have been well defined in the course of experiments. The thermal conductivity of the polycrystalline hexagonal-iron foil has been determined up to pressure 70 GPa and temperature 2000 K. At these conditions, the conductivity value of 32±7 W/m K was found. Sources of errors arising from uncertainties in input parameters and applied experimental procedures are discussed. Considering results of earlier preferred-orientation studies in diamond anvil cell, an averaging effect of polycrystalline texture on the intrinsic anisotropy is assumed. The obtained conductivity is interpreted as an effective value, falling in between the upper and lower bounds on the average conductivity of a random aggregate of uniaxial crystals.