Bi2Se3 Compound Research Articles

Density of states effective mass of SnBi4Se7 deduced from the temperature dependence of electrical conductivity in the activation regime

Current–voltage (I–V) measurements on polycrystalline samples of Bi2Se3 and stoichiometric ternary compound in the quasi-binary system of SnSe–Bi2Se3 at different temperatures in the vicinity of room temperature have been performed. Also, temperature dependence of electrical conductivity has been measured. From the analysis of the temperature dependence of electron concentration in the activation regime above room temperature, the density of states effective mass, m*, has been determined. Some intrinsic and contact properties such as barrier heights, ideality factors, and carriers concentrations have been investigated using I–V characteristics. It has been found that all samples exhibit ohmic and space charge limited conduction at low and high fields, respectively.

Impurity band in SnBi4Se7: thermoelectric power and electrical resistivity measurements

Thermoelectric power and electrical resistivity measurements on polycrystalline samples of Bi2Se3 and stoichiometric ternary compound in the quasi-binary system SnSe–Bi2Se3 in the temperature range of 90–420 K are presented and explained assuming the existence of an impurity band. The variation of the electron concentration with temperature above 300 K is explained in terms of the thermal activation of a shallow donor, by using a single conduction band model. The density of states effective mass m*=0.15m0 of the electrons, the activation energy of the donors, their concentration, and the compensation ratio are estimated. The temperature dependence of the electron mobility in conduction band is analyzed by taking into account the scattering of the charge carriers by acoustic phonon, optical phonon, and polar optical phonon as well as by alloy and ionized impurity modes. On the other hand, by considering the two-band model with electrons in both the conduction and impurity bands, the change in the electrical resistivity with temperature between 420 and 90 K is explained.

The Effect of Powder Size on Thermoelectric Properties of 95%Bi<sub>2</sub>Te<sub>3</sub>-5%Bi<sub>2</sub>Se<sub>3</sub> Alloy

The n-type (95%Bi2Te3- 5%Bi2Se3) compound was newly fabricated by gas atomization and hot extrusion, which is considered to be a mass production technique of this alloy. The effect of powder size on thermoelectric properties of 0.04% SbI3 doped 95%Bi2Te3- 5%Bi2Se3 alloy were investigated. Seebeck coefficient (α) and Electrical resistivity (ρ) increased with increasing powder size due to the decrease in carrier concentration by oxygen content. With increasing powder size, the compressive strength of 95%Bi2Te3-5%Bi2Se3 alloy was increased due to the relative high density. The compound with ~300 μm size shows the highest power factor among the four different powder sizes. The rapidly solidified and hot extruded compound using 200~300 μm powder size shows the highest compressive strength.

Electrical conduction of SnBi4Se7

Polycrystalline samples of Bi2Se3 and stoichiometric ternary compounds in the quasi-binary system SnSe-Bi2Se3 were characterized by measurements of temperature and field dependence of electrical conductivity. The current density–electric field characteristics were found to be non-linear, especially when the applied electric field exceeds a certain value which is dependent on the temperature T. Furthermore, the electrical conductivity can be enhanced by the applied electric field. The characteristic length a(T) seemed to be enhanced with increasing temperature. Electrical conductivity measurements elucidated the semiconducting behaviour of both compounds, especially when the temperature of measurement exceeds a certain value for SnBi4Se7, and hopping and band type conduction are dominant at low and high ranges of temperature, respectively. Below 200 K, the electrical conductivity of SnBi4Se7 decreases with increasing temperature. Meanwhile, additional scattering and hopping seemed to characterize the behaviour of SnBi4Se7 due to the Sn doping of Bi2Se3 resulting in additional states at the Fermi level.

Improving Hardness and Thermoelectric Performance in Pseudo-ternary Thermoelectric Alloys (Bi2Te3)(Bi2Se3)(Nd2Te3)

The solid solution of three elements Bi, Te and Se is known to be an appropriate n-type thermoelectric (TE) module. Although it shows high TE performance, it suffers from low hardness. Neodymium (Nd) is an appropriate element that can be introduced into the solid solution to overcome this problem. The TE and microstructural properties dependence on the amount of Nd addition in different into Bi2(Te1-xSex)3 are studied. The mechanical durability of the (Bi2Te3)(Bi2Se3)(Nd2Te3) compounds had been evaluated as a function of Nd2Te3 content (0.0–0.4% mole), the solubility limit of 0.12% mole Nd2Te3 in Bi2Te2.88Se0.12 is obtained. The samples are characterized by phase formation and hardness measurements. The optimum figure of merit of 3.06 ×10-3 K-1 at 300 K is obtained using 0.12% mole Nd2Te3, with the corresponding 2.5 kg·mm-2 of hardness. Finally, vast studies of the TE parameters of defined compound in the temperature range of 300–500 K are performed.

Preparation and thermoelectric power of SnBi4Se7

Polycrystalline samples of Bi2Se3 and a stoichiometric ternary compound in the quasi-binary system SnSe–Bi2Se3 have been prepared and characterized by X-ray powder diffraction analysis. At room temperature the carrier concentration values are n = 1.1 × 1019 cm−3 for Bi2Se3 and n = 0.53 × 1019 cm−3 for SnBi4Se7. The thermoelectric power has been measured over the temperature range 90–420 K. The thermoelectric power of Bi2Se3 is higher than that for SnBi4Se7, which shows that the Sn impurity has an acceptor character. Therefore, doping Bi2Se3 with tin atoms does not improve thermoelectric properties of this material, due to decrease the value of the power factor σS 2. Transport properties of the studied polycrystalline samples are characterized by a mixed transport mechanism of free carriers. It is necessary to add more than one Sn atom to the Bi2Se3 compound in order to suppress the electron concentration by one electron. Such behaviour of the dopant is explained by the formation of various structural defects. Besides the dominant substitutional defect, SnBi, tin atoms also form uncharged defects, corresponding to seven-layer lamellae of the composition Se–Bi–Se–Sn–Se–Bi–Se which corresponds to the structure of the SnBi2Se4.

Mn-doped V2VI3 semiconductors: Single crystal growth and magnetic properties

We have grown Mn-doped V2VI3 single crystals using the temperature gradient solidification method. We report on the structural and magnetic properties of Mn-doped Bi2Te3, Sb2Te3, Bi2Se3, and Sb2Se3 compound semiconductors. The lattice constants of several percent Mn-doped V2VI3 were slightly smaller than those of the undoped V2VI3 due to the smaller Mn atomic radius (1.40Å) than those of Bi (1.60Å) and Sb (1.45Å). Mn-doped Bi2Te3 and Sb2Te3 had ferromagnetic ordering at TC=10 and 17K, respectively. However, Mn-doped Bi2Se3 and Sb2Se3 showed spin glass and paramagnetic properties, respectively.

Optimization of thermoelectric properties of Bi2Se3 using insertion techniques

In this work we investigate the optimization of the performance of thermoelectric materials using insertion techniques. Our results indicate that in cases such as Bi2Se3 compounds, where insertion of foreign species in the lattice is possible due to the particular crystal structure, the insertion technique could be proven to be a valuable easy to apply and cost effective technique, an alternative to doping, that can produce homogeneous materials with fine tuning of the electronic and thermoelectric properties.

Modification of Thermoelectric Properties Using Insertion Techniques

AbstractIn this work is presented the application insertion techniques for the modification of the performance of thermoelectric materials. The results indicate that in cases as in Bi2Se3 compounds where insertion of foreign species in the lattice is possible due to its particular crystal structure, the insertion technique could be proved a valuable easy to apply and cost effective, alternative to doping technique. The techniques can produce homogeneous materials with electronic and thermoelectric properties finely tuned.