Effect of doping with rare-earth elements (Eu,Tb, Dy) on the conductivity of Bi2Te3 layered single crystals

The temperature dependences of the resistivity in the directions parallel and perpendicular to the layer plane in the range of temperatures T = 5–300 K and the Hall and transverse magnetoresistance effects (magnetic fields <80 kOe, T = 5 K) are studied for doped and undoped Bi₂Te₃ layered single crystals. It is shown that, upon the doping of Bi₂Te₃ crystals with atoms of rare-earth elements (Eu, Tb, Dy), the resistivity in the directions parallel and perpendicular to the layer plane in Bi₂Te₃ increases. The increase in the resistivity is caused mainly by a decrease in the charge-carrier mobility because of an increased contribution of charge-carrier scattering at defects to scattering processes. The charge-carrier concentrations and mobilities as well as the Hall factor defined by the anisotropy of the effective masses and by the orientation of ellipsoids with respect to the crystallographic axes are estimated.

     

Controlling the Heating of a Rod Using the Current and Preceding Time Feedback

Automation and Remote Control - Using the process of heating a rod in a furnace as an example, we study the feedback control synthesis problem for plants with distributed parameters. To form the...     

Raman scattering in ZnGa2Se4 single crystals

The raman spectra of ZnGa₂Se₄ single crystals are studied at 300 K in various experimental configurations. The observed phonon frequencies are identified by their types of symmetry. The optical phonon frequencies are related to particular atomic displacements in the unit cell.     

Seismic stratigraphy of the Upper Pliocene and Quaternary deposits in the South Caspian Basin

More than 10,000 km of seismic data were used for seismic stratigraphic analysis and differentiation of major depositional environments of Upper Pliocene and Quaternary strata in the central deepwater and eastern parts of the South Caspian Basin (SCB). The study shows that the conventional sequence stratigraphy concept works well in the South Caspian Basin. Clinoform complexes within Paleo-Amudarya shelf margin are bounded by regionally, seismically expressed sequence boundaries and flooding surfaces that can be traced to the deep basin. Sequence analysis and seismic facies interpretation showed that deposition of prograding clinoforms and deep-water turbidite systems were controlled by the relative lake-level change. Depositional interpretation of sediment infill indicates that in the South Caspian Basin, as in other closed basins with high terrigineous input, basinal deposition is from turbidity currents and slumps generated from large shelf-edge deltas. There are two distinct stratigraphic complexes interpreted from seismic data: lower, interpreted as homogeneous infill of mud-rich turbidites and deepwater lacustrine deposits (Upper Pliocene, i.e. Akchagyl and Aspheron), and upper, consisting of prograding clinoform packages and coeval deepwater fan systems and slumps (Quaternary). The source of the central basin turbidite infill was primarily the eastern “Paleo-Amudarya” shelf. Growing diapir folds structurally controlled deposition of large-scale fan systems in the central basin. The distribution of these fan systems is tied to location of the coeval thick shelf-margin complexes.     

An electron diffraction study of the ZnIn2Se4 crystal structure: A novel phase

A novel layered-structure ZnIn₂Se₄ phase has been obtained. Texture electron diffraction patterns aid in the identification of a crystal structure with lattice parameters a = 4.045 Å and c = 52.29 Å, space group R m, and z = 4.5. Crystal electron diffraction patterns displayed superstructural reflection, thus indicating a √3-fold increase in the a parameter. The similirity of reflection locations and intensities both on the crystal rotation electron diffraction pattern and on texture electron diffraction patterns showed that no phase transition occurred on specimen pounding. Electrophysical and optical parameters (E_g = 1.68 eV; N = 8 × 10²² m^-3; = 0.1Ωm) are studied at 300 K. The Hall coefficient is constant (R_H = 7.2 × 10^-5m³C^-1, mobility μ = 8 × 10^-3m²V^-1s^-1 at 200–300 K.     

Effect of annealing on the structure of Bi2Te3-Bi2Se3 films

The crystallization dynamics of Bi₂Te₃-Bi₂Se₃ polycrystalline films annealed at 200–230°C has been investigated. The formation of ordered blocks 70—150 nm in size, depending on the annealing time and temperature, is observed.     

Phonon drag of electrons in Ag<Subscript>2</Subscript>S

The temperature dependences of the heat-conductivity coefficient χ and the thermopower 6h of Ag₂S are investigated in the range of 4.2–300 K. It is found that the value of 6h sharply increases (6h ∞ T^-3) with decreasing T at T < 100 K and passes through a maximum at 16–18 K. The heat-conductivity coefficient passes through a maximum at ≈30 K. The sharp increase in 6h is found to be caused by the effect of long-wavelength-phonon drag of electrons. It is shown that the shift of the 6h and χ peaks, as well as the temperature dependence of the phonon thermopower 6h_ph ∞ T^-3, agrees with the Herring theory.     

The piezoresistive effect in the p-TlInSe2 single crystals

The experimental investigations of the directed deformation influence on the electroconductance of p-T1InSe₂ single crystals have been carried out. The presence of a strong piezoresistive effect has been found at p-T1InSe₂ crystal tension or compression along the crystallographic axis [001]. It is shown that the observed effect has a qualitative explanation, based on a 4-ellipsoidal model with the more probable arrangements of extrema being at Г, T, and N points of the Brillouin band.     

Constitutional diagram and physical properties of TlSeInSe pseudobinary system

In this study a physicochemical analysis of the TlSe-Inse semiconductor system has been performed, and the existence of the TlInSe₂ compound with congruent fusion at 808 ± 5°C has been established. The electrophysical properties of Tl_xIn_1−xSe (0 ? X ? 1) system single-crystals of certain compositions have also been studied.