An anomaly in the magnetic susceptibility of the Mg1−x CuxO solid solutions with 0.01≤x≤0.20

The problem of localized superconductivity has motivated the preparation of Mg_1−x Cu_xO solid solutions with NaCl structure and 0.01≤x≤0.20, as well as a study of the magnetization and magnetic susceptibility χ in the 2–400 K temperature range and in magnetic fields of up to 5 T. The temperature dependence of χ is described for all compositions by the Curie-Weiss law, χ = C/(T − θ), where the constant C is close to the value calculated for each composition for μ_eff = 1.7–1.9μ_B, and θ is close to zero. For T < 30 K, χ(T) deviates for all compositions toward lower χ, which can be attributed to magnetic ordering of exchange-coupled clusters in the solid solution. At T∼320–330 K, an anomaly of a diamagnetic type, i.e., a decrease of χ by 6–30% of its paramagnetic value, has been observed for all compositions against the background of the generally paramagnetic χ(T). A discussion is presented of alternative reasons for this anomaly and of its possible connection with localized superconductivity. __________ Translated from Fizika Tverdogo Tela, Vol. 42, No. 4, 2000, pp. 701–703. Original Russian Text Copyright ? 2000 by Samokhvalov, Arbuzova, Viglin, Naumov, Smolyak, Korolev, Lobachevskaya.     

Width of the ferromagnetic resonance line in highly dispersed powders of crystalline and amorphous Co-P alloys

The resonance characteristics (inhomogeneous FMR linewidth ΔH) in highly dispersed (d=0.1–3 μm) powders of crystalline and amorphous Co-P alloys are investigated as a function of the composition, particle size, and atomic structure. It is established that ΔH for powders of amorphous Co-P alloys is two to three times larger than ΔH for crystalline Co-P powders. According to the investigations performed, this is caused by thermodynamically stimulated segregation of nonmagnetic Co₂P inclusions, apparently an effective relaxation channel, in the amorphous state of Co-P powders. Fiz. Tverd. Tela (St. Petersburg) 41, 464–467 (March 1999)     

Magnetic and electrical properties of Mg1−x CuxO solid solutions and magnetic shielding in Cu-Mg1−x CuxO structures

Mg_1−x Cu_xO solid solutions having an NaCl structure with 0⩽x⩽0.20 are synthesized and Cu-Mg_1−x Cu_xO structures are prepared for superconductivity studies. The magnetic susceptibility χ, electron paramagnetic resonance (EPR), and electrical conductivity of the solid solutions are studied at temperatures of 5–550 K. It is shown that χ ⁻¹(T) obeys the Curie-Weiss law with a paramagnetic Curie temperature Θ close to zero and an effective magnetic moment μ _eff=1.9 μ _B, close to the 1.73 μ _B of a Cu²⁺ ion with spin S=1/2. The width ΔH of the EPR line depends weakly on temperature and increases as x is raised. The volume narrowing of the EPR linewidth ΔH is used to estimate the exchange interaction parameter, 3×10⁻⁴ eV. The g-factor is close to 2 and is temperature independent. The electrical conductivity of Mg_1−x Cu_xO at T=300 K is ≈10⁻¹¹–10⁻¹² Ω⁻¹ cm⁻¹ for x=0 and increases to 10⁻⁵–10⁻⁶ Ω⁻¹ cm⁻¹ for x=0.15–0.20. The conductivity is p-type. Magnetic shielding is observed in Cu-Mg_1−x Cu_xO structures with x=0.15 and 0.20. The possible connection of this phenomenon with interference superconductivity in the contact layer of the structure is discussed. Fiz. Tverd. Tela (St. Petersburg) 41, 293–296 (February 1999)     

Model of current and optical conductivity switching in YBa2Cu3O7−x films

A model is proposed for the thermal and electrical responses of films of the high-T _c superconducting material YBa₂Cu₃O7_7−x to current and optical pulses. Numerical calculations are compared with experimental data for current pulses of duration 100 μs and laser pulses of duration 0.1 ns; this yields improved data on the thermal conductivity of thin YBa₂Cu₃O7_7−x films (1.5–2 W/m·K) and thermal resistance of the film-substrate contact (5×10⁻⁸m²·K/W) in the neighborhood of the superconducting transition. This model can be used for optimizing the film structure parameters and control regimes for switching elements for pulses lasting longer than 0.1 ns. Zh. Tekh. Fiz. 69, 77–82 (October 1999)     

Determination of the depth of formation of magnetooptical effects in CoNi films

The optical constants of CoNi films with magnetic properties that are nonuniform across their thickness are determined in reflected light by two methods, viz., optical and magnetooptical measurements. The values of the parameters L=λ/4πk and Z ₀=λ/8n, one of which (specifically, the one which has the smaller value at a given value of λ) determines the depth of formation of reflective magnetooptical effects (l _mo) according to the current theories, are calculated on the basis of the values obtained for the optical constants n and k of the films (λ is the wavelength of the light used, and n and k are the refractive index and the absorption coefficient of the magnet). It is established for the CoNi films investigated that l _mo is determined by L and varies from about 200 to 300 ? in the range 0.33 μm⩽λ⩽0.83 μm. In CoNi films, which are inhomogeneous across their thickness and are characterized by significant variation of the magnetic properties over distances ∼l _mo, variation of the form of the magnetization curves determined by measuring the equatorial Kerr effect is observed as λ increases. Zh. Tekh. Fiz. 68, 69–72 (February 1998)     

Structure of the free exciton luminescence band of heteroepitaxial ZnSe/GaAs layers

The exciton reflectance and photoluminescence spectra of epitaxial ZnSe/GaAs layers with a thickness of 2–4 μm are investigated in the temperature range 10–120 K. It is shown that one of the causes of the formation of the doublet structure of the A _n=1 photoluminescence band is interference of the exciton radiation at the boundaries of the near-surface dead layer. Fiz. Tverd. Tela (St. Petersburg) 40, 881–883 (May 1998)     

Nature of the nonlinear second-order optical susceptibility in molecular materials with C 2v molecular symmetry

The method of second-harmonic generation at the wavelength 1.06 μm is used to study the nonlinear second-order optical susceptibility of polycrystalline molecular materials with C _2v molecular symmetry belonging to the group of 2,6-dibenzadiene substituted cyclohexanes. The magnitude of the second harmonic signal is comparable to or greater than its value for polycrystalline urea and depends on the type of substituent (the stronger the donor properties of the substituent, the stronger the signal). It is shown that in the majority of the compounds investigated the large nonlinear optical polarizability observed is associated with the octupole moment of the molecule. Fiz. Tverd. Tela (St. Petersburg) 39, 1687–1689 (September 1997)     

Determination of amorphous layers on thick film Nasicon in dependence on different sintering processes

In thick film gas sensors Nasicon is used as a solid electrolyte with high Na⁺ ionic conductivity. Sensors like CO₂, O₂, Pt ▮ Na₂CO₃, BaCO₃ ∥ NASICON [Pt]_glass, O₂, CO₂ are suitable to measure the CO₂-concentration over 5 orders of magnitude. To characterize the screen printed Nasicon as a main component of such sensors grazing incidence diffractometry (GID), SEM, impedance spectroscopy and dc polarization measurements are performed in order to improve the long-term stability. The sintering process of the thick film influences the chemical surface composition of Nasicon and as a consequence the response of the sensor. Nasicon films sintered at temperatures between 1070 and 1210 °C show an amorphous layer increasing up to 1.1 μm thickness on the surface. Impedance measurements show, that cells using in such a way prearated Nasicon are responsible for water vapour. Paper presented at the 1st Euroconference on Solid State Ionics, Zakynthos, Greece, 11 – 18 Sept. 1994     

Comparison of optical properties and mechanical/electrical degradation of some low density polyethylene-and polypropylene-based polymer blends

In this study, the optical properties as well as mechanical and electrical degradation of low-density polyethylene (LDPE)/polypropylene fiber (PP fiber) (10–50% PP fiber), polypropylene (PP)/PP fiber (10–50% PP fiber), and LDPE/diamond (0.1–3% diamond) blends, which are prepared by hot pressing method, with changing thicknesses ranging from 30 to 225 μm, are compared. The spectra, in the wavelength range 200–2500 nm, are examined. Based on optical absorption spectra obtained, Tauc graphs are plotted. Determined values of the direct optical energy gap (E _d ^opt ), the indirect optical energy gap (E _i ^opt ), the width of the band (ΔE), and ultraviolet transmittance (T_UV) are listed. The direct E _d ^opt and indirect E _i ^opt values for organic blends are in the range of 3.10–3.17 eV and 1.52–2.99 eV; for inorganic blends they are 1.80–4.13 eV and 1.55–4.7 eV respectively. The electrical strength (ε) and the mechanical tension (σ) have been investigated, and graphs (the dependence of the electrical life time log τ_ε on ε) are given. The experimental results are analyzed from the viewpoint of the validity of the thermofluctuation theory. LDPE and LDPE/0.5% diamond composite parameters consecutively changed: σ from 68 to 82 MPa, ε from 60·10⁶ to 85·10⁶ V/m, mechanical lifetime τ_σ from 10 to 1.5·10⁵ sec, electrical lifetime τ_ε from 2· 10³ to 2·10⁵ sec, and structure-sensitive parameters γ and χ — from 1.48 to 1.18 (J)MPa/mole and from 0.97 to 0.70 (J)Vm⁻¹/mole respectively. The values of mechanical and electrical durability were observed to increase by 20 and 41%, respectively, for LDPE/0.5% diamond composite. Published in Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 5, pp. 677–683, September–October, 2007.     

Heating effects in stimulated photon echo spectroscopy of low-temperature glasses

Photon echo spectroscopy has been extensively used to characterize the low-temperature relaxations in amorphous solids. However, the relatively high excitation energies used in the actual experiments (20–200μJ/g) lead to serious problems with sample heating since the specific heat of amorphous solids is on the order of 300μJ/gK at 2 Kelvin. We present data for the amorphous system polymethylmethacrylate and discuss the different contributions to the heating process. Presented at the Czech-Israeli-German Symposium “Dynamical Processes in Condensed Molecular Systems”, Prague, Czech Republic, 26–30 May 1997.     

Crystallization of Ge2Sb2Te5 phase—change optical disk media

In this paper, the crystallization behaviour of amorphous Ge₂Sb₂Te₅ thin films is investigated using differential scanning calorimetry), x-ray diffraction and optical transmissivity measurements. It is indicated that only the amorphous phase to face-centred-cubic phase transformation occurs during laser annealing of the normal phase-change structure, which is a benefit for raising the phase-change optical disk's carrier-to-noise ratio (CNR). For amorphous Ge₂Sb₂Te₅ thin films, the crystallization temperature is about 200℃ and the melting temperature is 546.87℃. The activation energy for the crystallization, E_a, is 2.25eV. The crystallization dynamics for Ge₂Sb₂Te₅ thin films obeys the law of nucleation and growth reaction. The sputtered Ge₂Sb₂Te₅ films were initialized by an initializer unit. The initialization conditions have a great effect on the reflectivity contrast of the Ge₂Sb₂Te₅ phase-change optical disk.     

Lithium ion conductivity of the B-site substitution in Li3xLa0.67−xRE y III Ti1−2yPyO3 system (REIII=Sc3+, Y3+, Nd3+, Sm3+, Eu3+, Yb3+)

The B-site substituted perovskite solid solution systems Li_3xLa_0.67−xRE_yTi_1−2yP_yO₃ (RE=Sc, Y, Nd, Sm, Eu, Yb) have been investigated. Perovskite solid solutions formed in the range of x=0.10, y<0.10 for RE=Sc³⁺, Y³⁺, Yb³⁺, x=0.10, y≤0.05 for RE=Nd³⁺, Sm³⁺, Eu³⁺. Li_0.3La_0.57Nd_0.05Ti_0.9P_0.05O₃ has the highest bulk conductivity of 4.31×10⁻⁴ S·cm⁻¹ and the highest total conductivity of 2.52×10⁻⁴ S·cm⁻¹ at room temperature in all prepared compositions. The compositions have low activation energies of about 24–30 kJ/mol in the temperature ranges of 298–523 K. SEM studies showed that the sample made by solid-state reaction has a sphere-like morphology and a rough particle with particle size of about 50 μm. The research results also indicated that the reaction temperature decreases and the electrochemical stabilities of the titanate-based perovskite-type solid solutions are improved by using RE³⁺ and P⁵⁺ replaced Ti⁴⁺ on B-site in the Li_3xLa_0.67−xTiO₃ parent.     

Growth of YBa2Cu3O7−x thin films on sapphire with a cerium-oxide sublayer

The possibility is demonstrated of preparing high-quality films of the high-temperature superconductor YBa₂Cu₃C_7-δ with thicknesses up to 2.6 μm by dc magnetron sputtering. It is found that inclusions consisting of CuO and YBa₂Cu₃O₈ coexist with the growing film and are “sinks” for defects, nonstoichiometric atoms, and mechanical stresses. Using x-ray diffraction and Rutherford backscattering, we find that the structural perfection of the films is improved by increasing the thickness when using the proposed fabrication technique. Zh. Tekh. Fiz. 69, 94–98 (January 1999)     

Third-order resonant optical nonlinearity from trans–cis photoisomerization of an azo dye in a rigid matrix

 We investigated the trans–cis photoisomerization of an azo dye in a rigid matrix and the resulting third-order resonant optical nonlinearity by means of the simple theoretical prediction of a two-energy-level system, thin-layer chromatography and H-NMR studies. A methylorange (MO), a methylred (MR), congored (CR) or a Disperse Red 1 (DR1) doped polyvinyl alcohol (PVA) or silica film was used as nonlinear optical material. The existence of equi-absorbing points, or isosbestic points in the absorbance spectrum change and the remarkable stationary transmittance to be independent of the action beam intensity enabled us to confirm the photoisomerization even in a rigid matrix. Then, we measured the third-order resonant optical nonlinearity of dichroism through the polarization absorbance spectrum measurement and determined the characteristic optical parameters of the photoisomerization in the film such as the quantum yields φ_T, φ_C, the thermal reaction constant K and the photoisomerization time constant by fitting the theoretical curve of the two-energy-level system to the observed temporal transmittance change after the action beam exposure of the MO/PVA film. The quantum yields were φˉ_T=0.36 and φˉ_C=0.38, respectively. The photoisomerization time constant of MO embedded in the PVA film was a few seconds. The thermal reaction constant K depended on the excitation beam intensity. Received: 20 June 1996/Revised version: 4 October 1996     

Structure and properties of the Ti-Si-N nanocrystalline coatings synthesized in vacuum by the electroarc method

Phase composition, defect substructure, and mechanical properties of the Ti-Si-N coating deposited on metal and ceramic-metal substrates by electroarc sputtering of the Ti-Si composite cathode in an ionized nitrogen atmosphere are investigated by the methods of modern materials science. It is established that coatings so formed with a thickness of ∼1–3 μm are superhard (H_v ∼ 50 GPa), and have the nanocrystalline structure (with crystalline sizes D = 7 nm) based on titanium nitride δ-TiN. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 46–51, February, 2007.     

Reference electrodes for low-temperature gas sensors

The behavior of sodium oxide bronzes in contact with sodium-conducting solid electrolytes in atmospheres of oxygen, carbon dioxide, hydrogen sulfide, and humid air was investigated. The exchange currents at the Na_xCoO_y/NASICON interface was determined. It is shown that among the sodium-cobalt oxide bronzes the β-phase of the composition Na_0.6CoO₂ is the most reversible one (exchange current 236 μA/cm²). Paper presented at the 1st Euroconference on Solid State Ionics, Zakynthos, Greece, 11–18 Sept. 1994     

Magnetic structure and properties of a bulk Fe72Al5P10Ga2C6B4Si1 alloy in the amorphous and nanocrystalline states

The structure forming under controlled crystallization of a bulk Fe₇₂Al₅P₁₀Ga₂C₆B₄Si₁ amorphous alloy has been studied using differential scanning calorimetry, transmission electron microscopy, and x-ray diffraction. Crystallization of the alloy was established to result in the formation of a nanocrystalline structure consisting of three phases. The domain structure and magnetic properties of amorphous and nanocrystalline samples were investigated using the magnetooptic indicating film technique (MOIF) and a vibrating-sample magnetometer. The coercive force and the saturation magnetization of the amorphous samples were found to be 1 Oe and 130 emu/g, respectively. It was shown that the formation of the nanocrystalline structure entails a dramatic decrease in domain size (down to 1–4 μm) as compared to an amorphous sample (∼1 mm). Simultaneously, a decrease in the saturation magnetization and a strong increase in the coercive force of the samples were observed. __________ Translated from Fizika Tverdogo Tela, Vol. 46, No. 5, 2004, pp. 858–863. Original Russian Text Copyright ? 2004 by Abrosimova, Aronin, Kabanov, Matveev, Molokanov.     

Phase transitions in a titanium-silicon system under laser treatment in alkanes

An investigation is made of the phase transitions taking place in a titanium-silicon composite exposed to λ=1.06 μm laser treatment in pentane and hexane. It is shown that the formation of titanium carbide, oxides, and silicides depends on the treatment parameters and conditions. The phase changes were investigated over the thickness of the film and their influence on the electrophysical parameters of the titanium-silicon contact was studied. Zh. Tekh. Fiz. 69, 63–66 (June 1999)     

Semiconducting properties of CoO thin films

This paper reports electrical properties of CoO thin films of different thickness in the range 0.375 – 7.95 μm. Both electrical conductivity and thermopower were measured at elevated temperatures (1223 – 1423 K) and under controlled oxygen partial pressure (5 − 2.1x10⁴ Pa). It was found that at low p(O₂) the electrical conductivity decreases with film thickness. The activation energy of the electrical conductivity (E_a) in air decreases with the oxide thickness from 0.56 eV at 0.375 μm to 0.52 eV for massive CoO while at low p(O₂)=5 Pa the E_a is independent of the thickness (E_a = 0.46 eV). The reciprocal of the p(O₂) exponent of the electrical conductivity (n_δ) in the range 1223 K – 1373 K is close to four for the 7,95 μm film and is about 3.5–3.7 for the 0.375 μm film. The electrical properties of the CoO thin films are considered assuming different defect structures in the bulk phase and the surface layer.     

Domain kinetics in the formation of a periodic domain structure in lithium niobate

The evolution of the domain structure in LiNbO₃ with polarization switching in an electric field is investigated experimentally. Special attention is given to the formation processes of a regular domain applicable to nonlinear optical devices. A new method based on the spontaneous backswitching effect is proposed for creating a regular structure with a period of 2.6 μm in LiNbO₃ with a thickness of 0.5 mm. Fiz. Tverd. Tela (St. Petersburg) 41, 1831–1837 (October 1999)