Electric and dielectric properties of solution-gas interface grown amorphous AgCl films

Electric and dielectric properties of solution-gas interface grown AgCl thin film capacitors (Al/AgCl/Al) of various thicknesses have been studied in the frequency range 10¹–10⁶ Hz at various temperatures (303–393 K). I–V characteristics show ohmic, space-charge-limited, and thermionic emission conduction mechanisms to operate at low, intermediate and high voltages respectively. Capacitance decreases with increasing film thickness and applied frequency while it increases with increase of temperature. Loss factor (tanδ), which shows a pronounced minimum with frequency, increases with the rise of temperature and (tanδ)_min shifts to a higher frequency. The large values of capacitance and dielectric constant (ɛ) in the low frequency region indicate the possibility of an interfacial polarization mechanism to operate in this region while electronic and ionic polarizations dominate in the high frequency region.     

β-Relaxation in polymethylacrylate studied by light scattering

Summary The relaxation processes of glass-forming polymethylacrylate have been studied in a wide temperature range above the glass transition temperatureT _g by means of light scattering measurements. Experimental spectra give evidence of a self-similar behaviourI(ω) ∝ ω^−(1−a) over a spectral range of 2–3 decades, consistent with the predictions of the mode-coupling theory. Different from the prediction of the theory, the value ofa is strongly temperature dependent. This behaviour has been attributed to the presence of a slow secondary relaxation located in the GHz frequency region, whose strength progressively increases with temperature. Paper presented at the I International Conference on Scaling Concepts and Complex Fluids, Copanello, Italy, July 4–8, 1994.     

Temperature dependence of the heat capacity and lattice constant of lanthanum and samarium hexaborides

The temperature dependence of isobaric heat capacity and [411] interplanar spacing in lanthanum and samarium hexaborides have been determined experimentally within the 5–300 K region. The variation of the lattice parameters and thermal expansion coefficients α(T) with temperature has been calculated. Fiz. Tverd. Tela (St. Petersburg) 40, 2051–2053 (November 1998)     

Determination of thin film refractive index and thickness by means of film phase thickness

A new approach for determination of refractive index dispersion n(λ) (the real part of the complex refractive index) and thickness d of thin films of negligible absorption and weak dispersion is proposed. The calculation procedure is based on determination of the phase thickness of the film in the spectral region of measured transmittance data. All points of measured spectra are included in the calculations. Barium titanate thin films are investigated in the spectral region 0.38–0.78 μm and their n(λ) and d are calculated. The approach is validated using Swanepoel’s method and it is found to be applicable for relatively thin films when measured transmittance spectra have one minimum and one maximum only.      

Magnetic and band parameters of (3HgS)1–x(Al2S3)x (x = 0.5) crystals doped with manganese

Investigations of magnetic susceptibility (χ) of (3HgS)_1–x (Al₂S₃) _x (x = 0.5) crystals doped with manganese investigated by the Faraday method in the range of Т = 77–300 K and Н = 0.25–4 kOe demonstrate that peculiar magnetic properties can be due to the presence of clusters of the Mn–S–Mn–S type in these crystals. Based on the investigation of kinetic coefficients of the crystals performed for Т = 77–300 K and Н = 0.5–5 kOe, it is established that the crystals demonstrate conductivity of the n-type, and their electric conduction only very slightly depends on the temperature and shows a maximum, the Hall coefficient is independent of the temperature, while the temperature dependences of mobility exhibit a maximum. Using the concentration dependence of the effective electron mass at the Fermi level, the width of the forbidden band, the matrix element of interatomic interaction, and the effective mass on the conduction-band bottom are obtained. Based on investigations by optical methods, the presence of direct optical interband transitions in the crystals is established and the value of the optical forbidden band (at Т = 300 K) is determined.     

Ferroelectric relaxor behaviour in Pb(Fe0.5Ta0.5)O3

The relaxor ferroelectric lead iron tantalate, Pb(Fe_0.5Ta_0.5)O₃ (PFT) is synthesized by Coulombite precursor method. The X-ray diffraction pattern of the sample at room temperature shows a cubic phase. The field dependence of dielectric response is measured in a frequency range 0.1 kHz — 1 MHz and in a temperature range from 173–373 K. The temperature dependence of permittivity (ɛ′) shows broad maxima at various frequencies. The frequency dependence of the permittivity maximum temperature (T _m ) has been modelled using Vogel-Fulcher relation.      

Thermal hysteresis of the permittivity of Li0.12Na0.88TayNb1?yO3 solid solutions (y ≥ 0.7) prepared under high or normal pressure

The structural characteristics and dielectric properties (ε′, tanδ) of Li_0.12Na_0.88Ta_yNb_1−y O₃ solid solutions (y ≥ 0.7) synthesized under high or normal pressure (HP and NP ceramics, respectively) were studied. It was established that these solid solutions have an orthorhombic perovskite structure (space group Pnma) in the paraelectric state. The temperature and frequency dependences of the dielectric properties of the solid solutions are described in terms of microinhomogeneity of a system containing ferroelectric clusters with an enhanced Nb content as compared to that in the matrix. The characteristics of the cluster system depend on the method by which the ceramics were prepared. The HP ceramic is more homogeneous on the microscale. The permittivity ε′ was found to undergo thermal hysteresis in the region from 200 to 400 K, the parameters of which strongly differ for the HP and NP ceramics. The temperature of the maximum ε′ obtained in cooling runs for the NP and HP ceramics is 50–60 and 110 K lower, respectively, than that on the heating branch. The hysteresis may originate from interaction of the antipolar mode condensing under cooling with nonpolar ordered distortions, which drives the system to the state of global minimum. When the system residing in this state is heated, this mode undergoes decondensation at a higher temperature. __________ Translated from Fizika Tverdogo Tela, Vol. 47, No. 4, 2005, pp. 679–685. Original Russian Text Copyright ? 2005 by Olekhnovich, Radyush, Vyshatko, Moroz, Pushkarev, Palatnikov.     

AC Conductivity,XRD and transport properties of melt quenched PbI<Subscript>2</Subscript>–Ag<Subscript>2</Subscript>O–Cr<Subscript>2</Subscript>O<Subscript>3</Subscript> system

Composite materials used for electrode and electrolyte materials have been intensely studied in view of their advantages such as higher conductivity and better operational performance compared to their single-phase counterparts. The present work aims at studying the electrical and structural characteristics of a new composite electrolyte namely, (PbI₂) _x  − (Ag₂O–Cr₂O₃)_100−x where x = 5, 10, 15, 20, and 25 mol%, respectively, prepared by the melt quenching technique. The room temperature X-ray diffraction spectra revealed certain crystalline phases in the samples. AC conductivity analysis for all the prepared samples was carried out over the frequency range 1 MHz–20 Hz and in the temperature window 297–468 K. The room temperature conductivity values were calculated to be in the order of 10⁻⁵–10⁻³ Scm⁻¹. An Arrhenius dependence of temperature with conductivity was observed, and the activation energies calculated were found to be in the range 0.27–0.31 eV. Furthermore, the total ionic transport number (t _i) values obtained for all these indicated the ionic nature of this system. Paper presented at the Third International Conference on Ionic Devices (ICID 2006), Chennai, Tamilnadu, India, Dec. 7–9, 2006.     

Asymptotic Behavior of the Magnetization Near Critical and Tricritical Points via Ginzburg–Landau Polynomials

The purpose of this paper is to prove connections among the asymptotic behavior of the magnetization, the structure of the phase transitions, and a class of polynomials that we call the Ginzburg–Landau polynomials. The model under study is a mean-field version of a lattice spin model due to Blume and Capel. It is defined by a probability distribution that depends on the parameters β and K, which represent, respectively, the inverse temperature and the interaction strength. Our main focus is on the asymptotic behavior of the magnetization m(β _n ,K _n ) for appropriate sequences (β _n ,K _n ) that converge to a second-order point or to the tricritical point of the model and that lie inside various subsets of the phase-coexistence region. The main result states that as (β _n ,K _n ) converges to one of these points (β,K), . In this formula γ is a positive constant, and is the unique positive, global minimum point of a certain polynomial g. We call g the Ginzburg–Landau polynomial because of its close connection with the Ginzburg–Landau phenomenology of critical phenomena. For each sequence the structure of the set of global minimum points of the associated Ginzburg–Landau polynomial mirrors the structure of the set of global minimum points of the free-energy functional in the region through which (β _n ,K _n ) passes and thus reflects the phase-transition structure of the model in that region. This paper makes rigorous the predictions of the Ginzburg–Landau phenomenology of critical phenomena and the tricritical scaling theory for the mean-field Blume–Capel model.     

Resonance microwave photoresistance of a two-subband electron system at large filling factors

The microwave photoresistance of a double GaAs quantum well with two occupied size-quantization sub-bands E ₁ and E ₂ has been studied at the temperatures T = 1.6–4.2 K in the magnetic fields B < 0.5 T. The microwave photoresistance of such a system has been found to have a maximum amplitude when the maximum of the magneto-intersubband oscillations with the number k = (E ₂ − E ₁)ℏω_c coincides with the maximum or minimum of the ω/ω_c oscillations, where ω is the microwave frequency and ω_c is the cyclotron frequency. It has been shown that the resonance photoresistance that appears in the kth maximum of the magneto-intersubband oscillations is determined by the condition ℏω/(E ₂ − E ₁) = (j ± 0.2)/k, where k and j are positive integers.