Dow-Bin Hyun

Electrical properties of the 85% Bi2Te3-15% Bi2Se3 thermoelectric material doped with SbI3 and CuBr

Abstract The temperature dependences of the Seebeck coefficient, resistivity, Hall coefficient, and carrier mobility of SbI3- and CuBr-doped 85% Bi2Te3-15% Bi2Se3 single crystals have been characterized at temperatures ranging from 77 to 600 K, and the degenerate temperature, scattering parameter, bandgap energy, and the effective masses of the electron and hole have been determined. The degenerate temperature of the 85% Bi2Te3-15% Bi2Se3 alloy is 103 K, and the scattering parameter is determined to be 0.1. The ratio of the electron to hole mobility b (= μ e μ h ) is 1.45, and the bandgap energy EG at 0 K of the 85% Bi2Te3-15% Bi2Se3 alloy is 0.245 eV which is higher than EG of the pure Bi2Te3. The effective mass of the electron and hole in the 85% Bi2Te3-15% Bi2Se3 alloy are me = 0.056 mo and mh = 0.065 mo, respectively.

Thermoelectric properties of the n-type 85% Bi2 Te3-15% Bi2 Se3 alloys doped with Sbl3 and CuBr

The temperature dependence of the Hall mobility, Seebeck coefficient, electrical resistivity, thermal conductivity, and figure-of-merit of the SbI3 and CuBr-doped 85% Bi2Te3-15% Bi2Se3 single crystals have been characterized at temperatures ranging from 77 K to 600 K. The scattering parameter in 85% Bi2Te3-15% Bi2Se3 single crystal was determined as 0.1 from the temperature dependence of the carrier mobility. With increasing the amount of Sbl3 or CuBr doping, the Seebeck coefficient of 85% Bi2Te3-15% Bi2Se3 decreased and the temperature at which the Seebeck coefficient shows a maximum shifted to higher temperature. Compared to the Sbl3-doped specimens, the CuBr-doped single crystals exhibited higher (m* / m0)3/2 μc, implying that CuBr is a more effective dopant to improve the material factor and thus the figure-of-merit of 85% Bi2Te3-15% Bi2Se3. The maximum figure-of-merit of 2.0 × 10−3/K and 2.2 × 10−3/K was obtained for 0.1 wt % Sbl3-doped specimen and 0.03 wt % CuBr-doped specimen, respectively.

Thermoelectric properties of the hot-pressed (Bi0.2Sb0.8)2Te3 alloy with addition of BN and WO3 powders

Thermoelectric properties of the (Bi0.2Sb0.8)2Te3 alloy, fabricated by mechanical alloying and hot-pressing, were investigated with addition of BN and WO3 powders as phonon scattering centers. The Seebeck coefficient and the electrical resistivity of the hot-pressed (Bi0.2Sb0.8)2Te3 alloy increased with increasing the volume fraction of BN and WO3. Although the thermal conductivity of the hot-pressed (Bi0.2Sb0.8)2Te3 alloy decreased with increasing the volume fraction of BN and WO3 due to the reduction of κel, the lattice thermal conductivity was not lowered. The figure-of-merit of the hot-pressed (Bi0.2Sb0.8)2Te3 alloy, 3.05 × 10−3/K without addition of BN and WO3, decreased with increasing the volume fraction of BN and WO3, because the increment of the electrical resistivity was much larger than the decrement of the thermal conductivity due to the grain refinement.

Formation of PbTe intermetallic compound by mechanical alloying of elemental Pb and Te powders

Abstract The PbTe intermetallic compound could be fabricated by mechanical alloying of elemental Pb and Te powders for 2 minutes at ball-to-powder weight ratio of 2 : 1. The lattice parameter of PbTe processed by mechanical alloying, 0.6462 nm, was in excellent agreement with the value of 0.6458 nm which was reported for PbTe powder fabricated by melting and grinding. In situ observation of the abrupt temperature rise during the ball milling process indicated that the PbTe intermetallic compound was formed by a self-sustained reaction rather than by diffusional reactions. There was no tendency for PbTe crystalline powders to be amorphized by mechanical alloying.

Thermoelectric properties of p-type (Bi,Sb)2Te3 alloys fabricated by the hot pressing method

P-type (Bi0.25Sb0.75)2Te3 powders were fabricated by melting/grinding and mechanical alloying processes. Thermoelectric properties of the hot-pressed (Bi0.25Sb0.75)2Te3 were characterized with the powder processing method, powder size, hot pressing temperature, and the amount of excess-Te dopant. Specimens fabricated by melting/grinding exhibited lower Seebeck coefficient, lower electrical resistivity and higher thermal conductivity, compared to the specimens prepared by mechanical alloying. 3 wt.% excess Te-doped (Bi0.25Sb0.75)2 Te3, fabricated by melting/grinding and hot pressing at 550°C, exhibited a figure-merit of 3.2 x 10-3/K. For 1 wt.% excess Te-doped specimen prepared by mechanical alloying and hot pressing at 550°C, a figure-merit of 3.05 x 10-3/K was obtained.

Thermoelectric properties of the hot-pressed Bi2(Te0.85Se0.15)3 alloy with addition of BN powders

Thermoelectric properties of the hot-pressed Bi2(Te0.85Se0.15)3 alloy were investigated with the addition of BN powders as phonon scattering centers. The Seebeck coefficient and electrical resistivity of the alloy increased as the volume fraction of BN increased. Although the thermal conductivity of the alloy decreased as the volume fraction of BN increased due to the reduction of Kel, the lattice thermal conductivity varied little. The figure-of-merit of the alloys, 1.6×l0-3/K without the addition of BN, decreased as the volume fraction of BN increased because the increment of the electrical resistivity was much larger than the decrement of the thermal conductivity due to grain refinement.

Thermoelectric Properties of N-Type Bi 2 (Te l−x Se x ) 3 Fabricated by Mechanical Alloying and Hot Pressing

Thermoelectric properties of polycrystalline Bi 2 (Te 1−x Se x ) 3 (0.05 ≤ x ≤ 0.25), fabricated by mechanical alloying and hot pressing, have been investigated. Formation of n-type Bi 2 (Te 0.9 Se 0.1 ) 3 alloy powders was completed by mechanical alloying for 3 hours at ball-to-material ratio of 5: 1, and processing time for Bi 2 (Te 1−x Se x ) 3 formation increased with Bi 2 Se 3 content x. Figure-of-merit of Bi 2 (Te 0.9 Se 0.1 ) was markedly increased by hot pressing at temperatures above 450°C, and maximum value of 1.9 × 10 −3 /K was obtained by hot pressing at 550°C. With addition of 0.015 wt% Bi as acceptor dopant, figure-of-merit of Bi 2 (Te 0.9 Se 0.1 ) 3 , hot pressed at 550°C, could be improved to 2.1 × 10 −3 /K. When Bi 2 (Te 1−x Se x ) 3 was hot pressed at 550°C, figure-of-merit increased from 1.14 × 10 3 /K to 1.92 × 10 −3 /K with increasing Bi 2 Se 3 content x from 0.05 to 0.15, and then decreased to 1.30 × 10 3 /K for x = 0.25 composition.

Thermoelectric Properties of P-Type (Bi 1−x Sb x ) 2 Te 3 Fabricated by Mechanical Alloying Process

Thermoelectric properties of polycrystalline (Bi 1−x Sb x ) 2 Te 3 (0.75 ≤ x ≤ 0.85), fabricated by mechanical alloying and hot pressing methods, have been investigated. Formation of (Bi 0.25 Sb 0.75 ) 2 Te 3 alloy powder was completed by mechanical alloying for 5 hours at ball- to-material ratio of 5: 1, and processing time for (Bi 1−x Sb x ) 2 Te 3 formation increased with Sb 2 Te 3 content x. When (Bi 0.25 Sb 0.75 ) 2 Te 3 was hot pressed at temperatures ranging from 300°C to 550°C for 30 minutes, figure-of-merit increased with hot pressing temperature and maximum value of 2.8 × 10 −3 /K could be obtained by hot pressing at 550°C. When hot pressed at 550°C, (Bi 0.2 Sb 0.8 ) 2 Te 3 exhibited figure-of-merit of 2.92 × 10 −3 /K, which could be improved to 2.97 × 10 −3 /K with addition of 1 wt% Sb as acceptor dopant.