Thermoelectric Properties of Semimetal and Semiconductor Bi1 –xSbx Foils and Wires

Semiconductors - The results of experimental investigations into the thermoelectric properties (electrical conductivity, thermoelectric power, and thermal conductivity) of microtextured foils and...     

Thermoelectric and Galvanomagnetic Properties of Layered n-Bi2 –xSbxTe3 –ySey Films

Semiconductors - The thermoelectric properties in the temperature range 4.2–300 K and magnetoresistance oscillations in strong magnetic fields at low temperatures are studied in...     

Thermoelectric Properties of Hot-Pressed β-K2Bi8Se13−x S x Materials

In this work, hot-pressed pellets of the K₂Bi₈Se₁₃ family of compounds were prepared for the first time. The pellet fabrication of selected members of the K₂Bi₈Se_13?x S _x series was studied. Sintering parameters, such as temperature, pressure, and duration, were investigated based on a statistical design- of-experiments approach to identify the optimum conditions for fabrication of high-quality pellets. These optimum conditions were then applied for the K₂Bi₈Se_13?x S _x series, and the thermoelectric properties of the stoichiometric members for x = 0, 4, 6, and 8 were studied. Doping experiments were also investigated using sulfur excess in the x = 6 member in an attempt to modify its properties.     

Substitution Solid Solutions FeGa3−x E x and Their Thermoelectric Properties

In this study we performed substitution experiments on the gallium site of the intermetallic semiconductor FeGa₃, to adjust the charge carrier concentration, and determined the thermoelectric (TE) properties of the resulting products. Isoelectronic species aluminium and indium, hole-doping zinc, and electron-doping germanium were chosen to find suitable substituent elements. The samples FeGa_3?x E _x (E = Al, In, Zn, Ge; x = 0.03, 0.05, 0.06, 0.10, 0.20) were prepared by liquid–solid–reaction with subsequent spark plasma sintering treatment. X-ray diffraction, metallographic, and microstructure analysis were used to determine chemical composition and to evaluate the suitability of the substitution element. For solid solutions FeGa_3?x Al _x and FeGa_3?x In _x the substitution concentrations were very low (x ≤ 0.02) and did not improve the TE properties of FeGa₃. The samples FeGa_3?x Zn _x had the expected p-type behaviour and slightly lower thermal conductivity than the binary compound. A substantial increase in the TE figure of merit was achieved for the solid solution FeGa_3?x Ge _x for which transition from semiconducting to metal-like behaviour was observed, with an additional decrease of thermal conductivity. The maximum ZT value of 0.21 was achieved for the composition FeGa_2.80Ge_0.20.     

Theoretical Modeling of the Thermoelectric Properties of Fe2Ti1 –xVxSn Heusler Alloys

Semiconductors - Theoretical calculations of the electron structure and Seebeck coefficient in Fe2Ti1 –xVxSn alloys for the cases of a fully ordered L21 and partially disordered B2 Heusler...     

Ellipsometric Studies of the Optical Properties of Bi2Se3 and Bi2Se3〈Cu〉 Single Crystals

Semiconductors - By spectroscopic ellipsometry, the imaginary and real parts of the dielectric functions of Bi2Se3 and Bi2Se3〈Cu〉 single crystals are obtained in the photon-energy...     

Thermoelectric Properties of Yb1−x (Er,Lu) x Al3 Solid Solutions

Ytterbium trialuminide (YbAl₃) has one of the largest thermoelectric power factors of known materials below room temperature, making it a material of interest for low-temperature thermoelectric devices. However, the high thermal conductivity, which is due to a combination of a large electronic thermal conductivity and a moderately large lattice thermal conductivity, is detrimental to the figure of merit. Substitution of different atoms on the Yb site was performed in order to assess their ability to favorably alter the electronic structure and/or reduce the lattice thermal conductivity. We have synthesized and studied the thermoelectric properties of the solid solutions of YbAl₃ with ErAl₃ and LuAl₃. Results for electrical conductivity, thermal conductivity, and Seebeck coefficient for several of these solid solutions over the temperature range of 80 K to 300 K are reported. Although most substituted samples are driven toward a metallic state, we find that for some compositions the figure of merit is enhanced relative to pure YbAl₃.     

Influence of V Doping on the Thermoelectric Properties of Fe2Ti1 –xVxSn Heusler Alloys

Semiconductors - The results of experimental investigation into Fe2Ti1 –xVxSn alloys (x = 0, 0.06, 0.15, and 0.2) are presented. It is established from the temperature dependences of the...     

Effects of Doping of Lead Sulfide with Silver on the Lattice and Optical Properties of Pb1 –xAgxS Solid Solutions

Semiconductors - Single-phase cubic Pb1 –xAgxS limited solid solutions based on PbS with a metal sublattice doped with Ag are produced. The maximal relative content of Ag in the Pb1...     

Enhanced Thermoelectric Properties of Hole-Doped Bi2−x Ba x Sr2Co2O y Ceramics

The influence of Ba doping on the thermoelectric properties of Bi_2?x Ba _x Sr₂ Co₂O _y (x = 0.00, 0.025, 0.05, 0.075, 0.10, 0.125, and 0.15) samples prepared by the solid-state reaction method was investigated from 333 K to 973 K. For the samples with x ≤ 0.075, the electrical resistivity decreased with increase of the Ba doping amount due to p-type doping and they exhibited metallic electrical conductivity behavior, whereas the samples with x ≥ 0.10 exhibited semiconductor-like electrical conductivity behavior. The Seebeck coefficients of all the samples decreased with increase of the Ba doping amount. The thermal conductivity first decreased for x ≤ 0.075, then increased with higher Ba doping amounts. As an overall result, the dimensionless figure of merit (ZT) of Bi_1.925Ba_0.075Sr₂Co₂O _y reached the maximum value of 0.245 at 973 K, being 41% higher than that of the undoped sample.     

InxAl1 –xN Solid Solutions: Composition Stability Issues

Semiconductors - The phase diagrams of the InxAl1 –xN solid solutions and conditions for their growth by magnetron sputtering and molecular beam and metalorganic vapor phase epitaxy are...     

Influence of La Doping on the Transport Properties of Bi1 –xLaxCuSeO Oxyselenides

Semiconductors - The transport properties of p-type oxyselenides with the chemical composition Bi1 –xLaxCuSeO (x = 0.02, 0.04, 0.06) are investigated. An analysis of the temperature...     

Impedance Characteristics of γ-Irradiated (TlGaSe2)1 –x(TlInS2)x Solid Solutions

Semiconductors - Charge transport in (TlGaSe2)1 –x(TlInS2)x solid solutions in the frequency range of 20–106 Hz before and after γ irradiation is studied using...     

Effect of Chromium Doping on the Thermoelectric Properties of Bi2Te3: Cr x Bi2Te3 and Cr x Bi2−x Te3

The thermoelectric (TE) properties of Bi₂Te₃ compounds intercalated and substituted with Cr, namely Cr _x Bi₂Te₃ and Cr _x Bi_2?x Te₃, respectively, have been investigated to study the influence of chromium on the TE properties of Bi₂Te₃. The Seebeck coefficients were found to be positive for all the samples in the temperature range between 300 K and 550 K. Although no effective enhancement of the Seebeck coefficient was observed, doping with Cr by means of either substitution or intercalation clearly not only improved the electrical conductivity but also lowered the thermal conductivity of Bi₂Te₃. As a result of the improvement, the figure of merit ZT is increased up to 0.8 and 0.65 at 300 K for 1% intercalated and 1% substituted Bi₂Te₃, respectively.     

Thermoelectric Properties of (Bi1−x Sb x )2S3 with Orthorhombic Structure

Thermoelectric properties of the substitution system (Bi_1?x Sb _x )₂S₃ have been investigated, where binary Bi₂S₃ and Sb₂S₃ are narrow-gap semiconductors. It is confirmed that metallic conduction, originating from mobile electrons due to production of sulfur vacancies, is observed in Bi₂S₃ over a wide temperature range below room temperature. In Sb₂S₃, mobile carriers are not created and insulating behavior is observed because of the considerably wide bandgap. Change of the carrier number by substitution of antimony contributes strongly to the thermoelectric properties (resistivity and Seebeck coefficient). As a result, the nondimensional figure of merit, ZT, decreases monotonically with increasing antimony content. The maximum value of ZT is obtained in Bi₂S₃ as ZT ≈ 0.1 at room temperature. It is pointed out that control of the carrier number, which is achieved by production of sulfur vacancies, is important to achieve high thermoelectric performance in the (Bi_1?x Sb _x )₂S₃ system. It is possible that the thermoelectric efficiency could be improved by control of the carrier concentration in the bismuth-rich region, including pure binary Bi₂S₃.     

Effect of Fe Substitution on Thermoelectric Properties of Fe x In4−x Se3 Compounds

Starting from elemental powder mixtures of Fe _x In_4?x Se₃ (x = 0, 0.05, 0.1, 0.15), polycrystalline In₄Se₃-based compounds with homogeneous microstructures were prepared by mechanical alloying (MA) and hot pressing (HP). With the increase of x from 0 to 0.15, the electrical resistivity and the absolute value of the Seebeck coefficient increased, while the thermal conductivity first decreased and then increased. The maximal dimensionless figure of merit ZT of 0.44 was obtained for the Fe _x In_4?x Se₃ (x = 0.05) sample at 723 K.     

Thermal Conductivity in Bi1−x Sb x Solid Solutions

Bi_1?x Sb _x solid solutions have attracted much attention as promising low-temperature thermoelectric materials. Previously, we observed distinct extrema in the isotherms of the transport and mechanical properties of polycrystalline Bi_1?x Sb _x and attributed their presence to the transition from diluted to concentrated solid solutions and to the reconstruction of the energy band structure under increasing Sb concentration. The goal of the present work is a detailed study of the concentration dependences of the thermal conductivity λ for Bi_1?x Sb _x polycrystalline solid solutions (x = 0 to 0.09) in the temperature range of 170 K to 300 K. It is established that the λ(x) dependences exhibit a nonmonotonic behavior: in certain concentration ranges an anomalous increase in λ with increasing x is observed. It is shown that the concentration dependences of the thermoelectric figure of merit calculated on the basis of the measured λ values are also nonmonotonic. The obtained data represent additional evidence in favor of our assumptions stated earlier about a significant effect of electronic phase transitions observed in Bi_1?x Sb _x solid solutions on the concentration dependences of their thermoelectric properties. These results should be taken into account when developing new Bi_1?x Sb _x -based materials.