Bi Se Alloys Research Articles

Traveling heater method에 의해 성장된 Bi2Te2.7Se0.3의 열전특성

Bi Te -Bi Se alloy which is typical n-type thermoelectric material were grown by traveling heater method (THM) technique. We investigate the effect of the composition of 100-x(Bi Te ) - x(Bi Se ) and doping of n-type dopants such as SbI and CdCl . Maximum figure of merit of Bi Te -Bi Se alloy was observed with CdCl 0.1 wt% (Z: 2.73 × 10 / K) and SbI 0.05 wt% (Z: 2.29 × 10 /K). Deviation along the length of Bi Te -Bi Se ingot grown by THM method is low, which indicates that the ingot is very homogenized. Also we observed the close relationship of between anisotropy ratio and dopant in the 90(Bi Te ) - 10(Bi Se ) alloys. And we confirmed the fact that anisotropy ratio exerts thermoelectric performance in Bi Te based n-type thermoelectric material.

Chemical bonding and surface interactions in Bi2Se3 and Bi4Se3

Topological insulators are a new class of materials that are insulators in the bulk but have near zero electron transport dissipation behavior on the surface. These surface states are topologically robust (resistant to impurities, defects, and geometry deformations), which makes these materials ideal candidates for a number of technological applications. Well-known three-dimensional topological insulators are bismuth selenide (Bi2Se3), which is composed of five-atom-thick layers that interact non-covalently with each other, and Bi–Se alloys resulting from combining these quintuple layers with elemental bismuth bilayers. In this article, we examine the surface sliding and binding energetics of the combinations of quintuple layers and bisumth bilayers found in Bi2Se3 and Bi4Se3. In addition, we investigate the nature of the chemical bonding in these systems and its relation to the surface energetics.

Ionic Conductivity in Liquid Sn-Se, Sb-Se and Bi-Se Alloys

Simultaneous measurements of ionic and electronic conductivities around the stoichiometric composition have been carried out on liquid Sn-Se, Sb-Se and Bi-Se alloys by applying the residual potential theory. The ionic conductivity, σ i , in liquid Sn-Se and Sb-Se alloys increases with increasing temperature, while, in liquid Bi-Se alloys, it decreases with increasing temperature. The isothermal σ i in liquid Sn-Se and Sb-Se alloys at higher temperatures exhibits a minimum at the stoichiometric composition of SnSe and Sb 2 Se 3 , respectively, and, on the other hand, it shows a maximum at Bi 2 Se 3 in liquid Bi-Se alloys. Values of σ i at SnSe, Sb 2 Se 3 and Bi 2 Se 3 near the melting temperature are 7.40 Sm -1 at 1173 K, 0.448 Sm -1 at 893 K and 45.3 Sm -1 at 993 K, respectively, which are about two orders of magnitude smaller than the corresponding electronic conductivities, σ e . The value of σ i of liquid Bi 2 Se 3 , which is the largest among three liquids, is roughly comparable to that for ionic liquid alloys such as Ag and Tl-chalcogenides. In contrast, liquid Sb 2 Se 3 indicates the smallest σ i due to the strong covalent bonding between unlike atoms. The minimum of the σ i -isotherm at SnSe and Sb 2 Se 3 in liquid Sn-Se and Sb-Se alloys also reflect the covalent nature in these liquids.

Structures of molten Tl- and Bi-chalcogen systems

Neutron diffraction studies on molten TlSe and BiSe alloys have been carried out over a wide concentration range. The total structure factors or the pair distribution functions of both systems are similar to those of the pure liquid metals in the metal-rich range. The existence of a covalent Se-type polymeric structure is recognized in the Se-rich composition range of the molten TlSe system. The partial structure factors were also derived, using three different total structure factors in a small concentration range, where the partial structure factors were assumed to be constant.

Neutron diffraction study of liquid BiSe alloys

The structure of liquid Bi 1− x Se x alloys with x = 0.3, 0.5, 0.6 and 0.65 was investigated to study the change in the chemical short-range order caused by a change of concentration. Neutron scattering experiments were carried out using the High Intensity Total scattering spectrometer (HIT) installed at the pulsed neutron source at the National Laboratory for High Energy Physics (KEK) in Tsukuba. The features of the structure factor, S( Q), are as follows. (i) S( Q) of Se-rich alloys has a hump on the low Q side of the first peak, the intensity of which decreases with increasing Bi concentration. (ii) The intensity of the second peak of S(Q) increases with increasing Se concentration. The change in the electronic property for the Se-rich alloys is closely related to the change in medium-range structure.

Neutron Diffraction Study of Liquid Bi–Se Alloys

A neutron diffraction study on the liquid Bi–Se alloys has been carried out over the wide composition range from Bi 2 Se 3 to pure Bi. An essential feature of the total structural functions is similar to those of pure liquid Bi in the Bi-rich range, suggesting that the additional Se atoms are almost substituted with the Bi atoms and they might form a certain short range order, because of the difference in the electronegativities of the constituents. The Bi–Bi configuration which is close to that of pure liquid Bi still remains in the Se-rich range. The partial structural functions have been estimated from the measured total structural data assuming their concentration independence.

Crystallization of Amorphous BiSe Alloys. Advantages and Limits of a Proposed Theoretical Model

Using experimental results obtained by DTA technique, the parameters controlling the crystallization of BiSe alloys are determined. The advantages and the limits of a proposed theoretical model are shown. Mit experimentellen Ergebnissen von DTA-Messungen werden die die Kristallisation von BiSe-Legierungen kontrollierenden Parameter bestimmt. Die Vorteile und Grenzen eines vorgeschlagenen theoretischen Modells werden aufgezeigt.

Heat capacities of liquid SbSe and BiSe alloys

Measurements of heat capacities for liquid SbSe and BiSe alloys were carried out up to 800°C using an adiabatic scanning calorimeter. Anomalous temperature variation of heat capacity was observed for liquid Sb 0.45Se 0.55, Sb 0.5Se 0.5 and Bi 2Se 3 alloys. Broad maxima were observed in the temperature dependence of their heat capacities. In contrast, the heat capacity for liquid Sb 2Se 3 alloys shows little temperature variation. In the concentration dependence, the maximum of the heat capacity deviates from the stoichiometric composition of M 2Se 3 in both alloy systems. The characteristic behaviour of the heat capacities for liquid SbSe and BiSe alloys can be attributed to a change in intermediate-range order and in local bonding.

Nature of deffects in amorphous Bi-Se alloys

Differential thermal analysis results on Bi x Se 1− x alloys (0 < x < 0.27) show that Bi atoms may be either three- or four-fold coordinated. Further measurements of dark conductivity show a sharp decrease of both resistivity and activation energy of conductivity between 1 and 2 at% of Bi. Comparison with other Bi-based alloys and chalcogenide alloys without Bi leads to the conclusion that Bi plays a particular role when allied with chalcogen materials. Considerations on the metallic character and electronegativity of Bi enable us to confirm that in Bi-based chalcogen alloys the Bi defects are four-fold coordinated and positively charged.

Electronic properties of liquid SbSe and BiSe alloys

AbstractThe electrical conductivity (σ), the magnetic susceptibility (χ), and the thermoelectric power (S) of liquid SbSe and BiSe alloys are measured as function of composition in the temperature range from the melting point to about 1000 °C. On adding Se to Sb and Bi σ indicates a rapid fall and χ has a sharp maximum of diamagnetism at the stoichiometric composition of M2Se3 in both the systems. A reversion of the sign of S is observed around the composition of Sb2Se3 in liquid SbSe alloys, while S in liquid BiSe alloys remains negative over a wide composition range including Bi2Se3. The calculated value of g (the ratio of real and free electron density of states at the Fermi level) using the observed values of σ begins to decrease in the vicinity of 50 at% Se and drops sharply at the concentration of 60 at% Se in both systems. Electronic properties obtained are discussed in the light of current transport theories employed in liquid semiconductors.

Activation energy of conductivity in amorphous Bi-Se alloys

The dark conductivity activation energy of Se 100− x Bi x amorphous alloys (0 ⩽ x ⩽ 27) shows a drastic decrease for x ≈ 2. This result may be connected with the transition from p-type to n-type conduction.

1199. Vapour pressure measurements in Bi-Se alloys: T Ohashi et al, Jap Inst Metals J, 30, 1966, 785–788 (in Japanese)

1199. Vapour pressure measurements in Bi-Se alloys: T Ohashi et al, Jap Inst Metals J, 30, 1966, 785–788 (in Japanese)