MnQ2 ( Q =S ,Se,Te)and [Mn(en) 3]Te4StructuresandTheir

The solvo-thermal technique is used for the synthesis of Te 4 (I).The crystal structure has been determined by single crystal X-ray diffraction techniques.The crystal belongs to the monoclinic, space group p 2 1/ c with unit cell: a =0.846 1(1), b =1.565 3(2), c =1.426 9(2) nm, α =90°, β =91.37(1) (3)°, γ =90°, V =1.889 3(4) nm 3,and Z =4.The results show that the structure contains a linear chain Zintl anion, 2- and a complex cation, 2+ . Optical studies have been performed on the powder sample of I, suggesting that the compound is a semiconductor with a band gap of 0.73 eV. The semiconductor properties for MnQ 2(Q=S,Se,Te) and Te 4 have been discussed by molecular orbital theory.     

Character of Interaction in the SnSb2Te4–SnBi2Te4 System and the Thermoelectric Properties of (SnSb2Te4)1 – x(SnBi2Te4)x Solid Solutions

Semiconductors - For the first time, the character of the interaction of components along the cut of SnSb2Te4–SnBi2Te4 is studied by various physicochemical methods in a wide temperature...     

MnQ2（Q=S,Se,Te）and [Mn（en）3]Te4 Structures and Their Semiconductor Properties

The solvo-thermal technique is used for the synthesis of [Mn(en)3]Te4 (I).The crystal structure has been determined by single crystal X-ray diffraction techniques.The crystal belongs to the monoclinic, space group p21/c with unit cell:a=0.8461(1),b=1.5653(2), c=1.4269(2)nm, α=90°,β=91.37(1) (3)°, γ=90°,V=1.8893(4)nm3,and Z=4.The results show that the structure contains a linear chain Zintl anion,[Te4]2-and a complex cation,[Mn(en)3]2+. Optical studies have been performed on the powder sample of I, suggesting that the compound is a semiconductor with a band gap of 0.73eV. The semiconductor properties for MnQ2(Q=S,Se,Te) and [Mn(en)3]Te4 have been discussed by molecular orbital theory.     

Thermoelectric Properties of Bi2 –xLuxTe2.7Se0.3 Solid Solutions

Semiconductors - The thermoelectric properties of compounds based on Bi2 –xLuxTe2.7Se0.3 solid solutions with x = 0, 0.05, 0.1, and 0.2 are studied. The samples for investigations are...     

Electrochemical Deposition and Characterization of Thermoelectric Ternary (Bi x Sb1?x )2Te3 and Bi2(Te1?y Se y )3 Thin Films

Thermoelectric thin films of the ternary compounds (Bi _x Sb_1?x )₂Te₃ and Bi₂(Te_1?y Se _y )₃ were synthesized using potentiostatic electrochemical deposition on gold-coated silicon substrates from aqueous acidic solutions at room temperature. The surface morphology, elemental composition, and crystal structure of the deposited films were studied and correlated with preparation conditions. The thermoelectric properties of (Bi _x Sb_1?x )₂Te₃ and Bi₂(Te_1?y Se _y )₃ films, i.e., Seebeck coefficient and electrical resistivity, were measured after transferring the films to a nonconductive epoxy support. (Bi _x Sb_1?x )₂Te₃ thin films showed p-type semiconductivity, and the highest power factor was obtained for film deposited at a relatively large negative potential with composition close to Bi_0.5Sb_1.5Te₃. In addition, Bi₂(Te_1?y Se _y )₃ thin films showed n-type semiconductivity, and the highest power factor was obtained for film deposited at a relatively small negative potential, having composition close to Bi₂Te_2.7Se_0.3. In contrast to Bi₂Te_2.7Se_0.3 thin films, an annealing treatment was required for Bi_0.5Sb_1.5Te₃ thin films to achieve the same magnitude of power factor as Bi₂Te_2.7Se_0.3. Therefore, Bi₂Te_2.7Se_0.3 thin films appear to be good candidates for multilayer preparation using electrochemical deposition, but the morphology of the films must be further improved.     

Effect of Excess Na on the Morphology and Thermoelectric Properties of Na x Pb1−x Te0.85Se0.15

The thermoelectric properties of p-Na _x Pb_1?x Te_0.85Se_0.15, which possesses a high thermoelectric figure of merit due to band convergence, have been systematically investigated for increasing Na concentration (x = 0.01, 0.02, 0.03, 0.05, and 0.07) from room temperature to 773 K. For x values up to 0.03, the hole concentration increases with the Na concentration; however, for x ≥ 0.03, excess Na forms separate microstructures with needle- and plate-like shapes. At high concentrations (x = 0.05 and 0.07) both the number and size of these structures increase (over 10 μm). Differential scanning calorimetry identifies a phase change near 660 K in samples with x = 0.05 and 0.07, confirming the formation of microstructures; this phase change leads to a decrease in electrical resistivity. However, these microstructures do not significantly affect thermal transport, probably because they are too large to scatter phonons. The highest thermoelectric figure of merit, zT, value is 1.6, which is obtained at 760 K for x = 0.05, due to the low thermal conductivity and electrical resistivity.     

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 Skutterudites Co4−x Ni x Sb11.9−y Te y Se0.1

CoSb₃-based skutterudites with substitution of Ni atoms for Co, and substitution of Te and Se atoms for Sb were successfully prepared by solid-state reaction and spark plasma sintering. According to x-ray diffraction analysis the major phase of all the samples had a CoSb₃-type structure, although back-scattered electron images showed that small amounts of impurity phases were present in all the samples. The temperature-dependent transport properties were characterized over the temperature range 300–800 K for all the samples. It was found that appropriate substitution with Ni, Te, and Se effectively improved the power factor and reduced the thermal conductivity. As a result, Ni, Te, and Se-tri-doped CoSb₃ materials with enhanced thermoelectric figures of merit, ZT, were obtained. The highest ZT was greater than 1.1 at high temperature.     

Thermoelectric Properties of Pulsed Electric Current Sintered Samples of AgPb m SbSe17 (m?=?16 or 17)

Lead chalcogenide materials have drawn attention in recent years because of their outstanding thermoelectric properties. Bulk n-type materials of AgPb _m SbTe_2+m have been reported to exhibit high figure of merit, ZT, as high as 1.7 at 700?K. Recent reports have shown p-type lead selenide-based compounds with comparable ZT. The analogous material AgPb _m SbSe₁₇ shares a similar cubic rock-salt structure with PbTe-based compounds; however, it exhibits a higher melting point, and selenium is more abundant than tellurium. Using solid solution chemistry, we have fabricated cast AgPb₁₅SbSe₁₇ samples that show a peak power factor of approximately 17???W/cm?K² at 450?K. Increasing the strength of such materials is commonly achieved through powder processing, which also helps to homogenize the source materials. Pulsed electric current sintering (PECS) is a hot-pressing technique that utilizes electric current through the die and sample for direct Joule heating during pressing. The mechanisms present during PECS processing have captured significant research interest and have led to some notable improvements in sample properties compared with other densification techniques. We report the thermoelectric properties of PECS samples of AgPb _m SbSe₁₇ along with sample fabrication and processing details.     

Nanostructuring and Thermoelectric Characterization of (GaSb)3(1−x)(Ga2Te3) x

GaSb is a promising thermoelectric material that exhibits good electrical properties. However, it has a high lattice thermal conductivity (κ _lat). Nanostructured bulk materials have been attracting interest because they effectively scatter phonons, significantly reducing κ _lat. AgPb _m SbTe _m+2 (LAST-m) compounds have recently been reported to have low κ _lat. These compounds have a NaCl structure, similar to that of binary PbTe, where Ag and Sb occupy the Pb site. In these compounds, two divalent Pb atoms are replaced with a monovalent Ag atom and a trivalent Sb atom to maintain charge compensation. In the present study, we reduced κ _lat of GaSb by applying the same principle as in LAST-m. Specifically, we substituted Te for Sb and generated vacancies at the Ga site to maintain charge compensation. This produced compounds with chemical compositions of (GaSb)_3(1?x)(Ga₂Te₃) _x (x = 0, 0.05, 0.10, and 0.25), where GaSb and Ga₂Te₃ both have the zincblende crystal structure. We employed two different annealing conditions: annealing at 833 K followed by quenching, and annealing at 833 K followed by cooling to room temperature over 3 days. The former annealed samples with compositions of x = 0.05 and 0.10 had nanoscale Ga-rich precipitates and exhibited a large reduction in κ _lat.     

Effect of Se Substitution on Structural and Electrical Transport Properties of Bi0.4Sb1.6Se3x Te3(1−x) Hexagonal Rods

In the current study, novel hexagonal rods based on Bi_0.4Sb_1.6Te₃ ingots dispersed with x amount of Se (x = 0.0, 0.2, 0.4, 0.6, 0.8, and 1.0) in the form Bi_0.4Sb_1.6Se_3x Te_3(1?x) were synthesized via a standard solid-state microwave route. The morphologies of these rods were explored using field-emission scanning electron microscopy (FESEM). The crystal structure of the powders was examined by x-ray diffraction (XRD) analysis, which showed that powders of the 0.0 ≤ x ≤ 0.8 samples could be indexed to the rhombohedral phase, whereas the sample with x = 1.0 had an orthorhombic phase structure. The influence of variations in the Se content on the thermoelectric properties was studied in the temperature range from 300 K to 523 K. Alloying of Se into Bi_0.4Sb_1.6Te₃ effectively caused a decrease in the hole concentration and, thus, a decrease in the electrical conductivity and an increase in the Seebeck coefficient. The maximal power factor measured in the present work was 7.47 mW/mK² at 373 K for the x = 0.8 sample.     

Correlation of the Optical and Magnetic Properties of Bi2Te3–Sb2Te3 Crystals

Semiconductors - The magnetic and optical properties of Bi2Te3–Sb2Te3 crystals are investigated depending on the ratio of Bi2Te3 and Sb2Te3 components in the solid-solution composition and...     

Improved Thermoelectric Properties of Se-Doped n-Type PbTe1−x Se x (0 ≤ x ≤ 1)

Enhancement of the thermoelectric figure of merit is of prime importance for any thermoelectric material. Lead telluride has received attention as a potential thermoelectric material. In this work, the effect of Se substitution has been systematically investigated in PbTe_1?x Se _x . The thermoelectric properties of synthesized alloys were measured in the temperature range of 300 K to 873 K. For the particular composition of x = 0.5, α was highest at ~292 μV/K, while k was lowest at ~0.75 W/m-K, resulting in the highest dimensionless figure of merit of ZT ≈ 0.95 at 600 K. The increase in thermopower for x = 0.5 can be attributed to the high distortion in the crystal lattice which leads to the formation of defect states. These defect states scatter the majority charge carriers, leading to high thermopower and high electrical resistivity. The dramatic reduction of the thermal conductivity for x = 0.5 can be attributed to phonon scattering by defect states.     

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.