Papers by Keyword: Thermopower

Abstract: In multi-layer structures impurity scattering is effectively reduced by the modulation doping in order to achieve high charge carrier mobility and, as a consequence, better device performance. In this paper, the thermoelectric properties of superlattices when electrons are scattered by strongly screened ionized impurities are discussed. In low-temperature and strong screening circumstances, dependence of the thermopower, power factor, and figure of merit on the superlattice period, miniband width, and screening radius is found. For the specified superlattice parameters and ionized impurity concentration, the figure of merit reaches the value of 2.6. The thermopower of the superlattices five times exceeds that of bulk samples.

Abstract: This paper presents the results of the experimental research on the electrical characteristics of two dissimilar thermoelectric power sources. Chromel-alumel and nichrome-constantan are the investigated types of thermocouples that are utilized as thermopower sources. Through the assistance of the collected data, experimental and theoretical studies of two equivalent thermopower sources are done. The first studied source is obtained by a parallel connection of the two types of thermocouples, and the second studied source is achieved by the parallel connection of two thermocouples of nichrome-constantan and a single thermocouple made of chromel-alumel. Theoretical studies of the two equivalent thermoelectric sources proved good repeatable precision of the studied results of experimental measurements.

Abstract: Thermopower α and magnetothermopower ∆α/α were studied in the Sm_0.55Sr_0.45MnO₃ samples, containing clusters of three types: ferromagnetic clusters with the Curie temperature T_C = 126 K, A-type antiferromagnetic clusters with the Neel temperature T_NA ≥ T_C and CE-type antiferromagnetic clusters with the T_NCE = 240 K. The curves of temperature dependence of α (T) have a large maximum including T_C and T_NCE and the sharp minimum on the {∆α/α}(T) curves in the T_C-region. Negative magnetothermopower in minimum achieves the giant value ~ 85% in magnetic field 14.17 kOe. It is shown that thermopower is largely caused by the presence of ferromagnetic nanoclusters of ferron-type and to a lesser degree of CE-type antiferromagnetic clusters, in which there is a charge ordering, displacing oxygen ions.

Abstract: Thermopower α and magnetothermopower α/α were studied in the single-crystal Sm_0.55Sr_0.45MnO₃ samples, containing clusters of three types: ferromagnetic clusters with the Curie temperature T_C = 134 K, A-type antiferromagnetic clusters with the Neel temperature T_NA T_C and CE-type antiferromagnetic clusters with the T_NCE = 240 K. The curves of temperature dependence of α (T) and {α/α}(T) have extrema in the T_NCE-region: large maximum on the first and sharp minimum on the second. Negative magnetothermopower in minimum achieves the giant value 50% in magnetic field 13,2 kOe. It is shown that thermopower is essentially caused by the presence of CE-type antiferromagnetic clusters, in which exists charge order, displacing oxygen ions

Abstract: Electrical properties of SnS films deposited by a thermal evaporation method have been investigated using the resistivity and thermopower measurements. The SnS films show p-type conduction at room temperature, and electrical activation energy of ~0.3 eV. Resistivity and Seebeck coefficient at room temperature were ~4×10¹ Ωm and +0.2 mV/K for as-deposited sample. The resistivity decreased ~1×10⁰ Ω·m and the Seebeck coefficient increased +0.27 mV/K when the sample was annealed at 400 °C. Crystallization and structural change cause the improvement of electronic transport with annealing treatment.

Abstract: The polycrystalline of Sr_1xLa_xMnO₃ (x = 0.11.0) samples were synthesized by solid state reaction method and general sintering. The Sr_1xLa_xMnO₃ powders were calcined and sintered by furnace at 900 K and 1173 K for 3 hours in air atmosphere, respectively. Thermopower of the samples were measured by steady state method at temperature range of 290-520 K in air. The thermopower all samples were increased with increasing the La content substitution.

Abstract: Electrical properties in dc-sputtered amorphous InGaZnO₄ films have been investigated using the thermopower and resistivity measurements. The amorphous InGaZnO₄ films show n-type conduction at room temperature, and electrical activation energy of ~0.47 eV. The resistivity and Seebeck coefficient at room temperature were ~2×10⁴ Ωm and 1.5 mV/K for as-deposited sample. The resistivity and Seebeck coefficient decreased to ~2×10⁰ Ω·m and 2.7 mV/K when the sample was annealed at 670770 K. Slow response of photocurrent was also observed. Partial crystallization and structural change cause the improvement of electron transport with annealing treatments.

Abstract: We report on electronic transport in nearly magnetic conductors with strong structural disorder. The initial motivation for this work was a large positive magnetoresistance (MR) found in magnetically ordered ground state of (Y1-xGdx)Co2 alloys. This was a surprising result since a large positive MR is not expected in a system with strong static magnetic or structural disorder. Contemporary theory of magnetotransport and common sense agree that an external magnetic field should suppress magnetic fluctuations, resulting in a negative MR. On the contrary; a positive MR suggests that an external magnetic field enhances static magnetic disorder. It was shown that unusual MR of (Y1-xGdx)Co2 alloys is related to a combination of structural disorder and metamagnetic instability of itinerant Co-3d electrons. The new mechanism of MR is common of a broad class of materials featuring a static magnetic disorder and itinerant metamagnetism. Such systems display a number of unusual properties, among them strong pressure and magnetic field dependencies of resistivity and thermopower, Non-Fermi-Liquid (NFL) behavior of resistivity and, possibly, of thermopower. We review the relevant experimental data, mostly the properties of RCo2-based alloys, and discuss the theoretical model developed for the interpretation of the experimental results. This model includes new mechanism of magnetoresistivity in structurally disordered itinerant magnetic alloys.

Abstract: For the study of stress state in engineering alloys, the thermopower (S) measurement could be acceptable method after a suitable calibration (fitting the S value to the change of well known other physical parameters like the magnetic coercive force, hardness or strength increase during various thermomechanical treatments). For this purpose a simple equipment is constructed and built by which the S shift can be measured versus the increasing mechanical tensile load. The first results will be published in this paper, obtained on various metallic glass ribbons.

Abstract: Quasi-one-dimensional sulfide BaVS3 is known to show a metal-to-semiconductor transition at ~70 K. In this study we investigated the effects of nonstoichiometry of BaVS3 on this transition. Single phase samples were obtained in the composition ranges of 0.95 ≤ 1±x ≤ 1.05 in BaV1±xS3, and of 0.95 ≤ 1-x ≤ 1.00 in Ba1-xVS3. All single phase samples showed the metal-to-semiconductor transition at ~70 K. Seebeck measurements revealed that the dominant carriers are electrons in all samples. BaV1.05S3 and Ba0.98VS3 showed relatively large values of the power factor of about 1.0 x 10-4W/K2m around 200 K.