Non-equilibrium and non-linear stationary states in thermoelectric materials

Abstract

Efficiency of thermoelectric materials is characterized by the figure of merit Z. Z has been believed to be a peculiar material constant. However, the accurate measurements in the present work reveal that Z has large size dependence and a non-linear temperature distribution appears as stationary state in the thermoelectric material. The observation of these phenomena is achieved by the Harman method. This method is the most appropriate way to investigate the thermoelectric properties because the dc and ac resistances are measured by the same electrode configuration. W e describe the anomalous thermoelectric properties observed in mainly (Bi,Sb) 2 Te 3 by the Harman method and then insist that Z is not the peculiar material constant but must be defined as the physical quantity dependent of the size and the position in the material.

Thermoelectric performance of quaternary Cu–Bi–Sb–Te alloys prepared by cold pressing

“…Bismuth telluride based alloy are known to be one of the current state-of-the-art thermoelectric materials used near room temperature, there is increasing interest in developing the materials with higher ZT values for direct energy conversion [1][2][3][4]. Kurosaki et al [5,6] prepared p-type polycrystalline-sintered materials Tl 9 BiTe 6 and TlSbTe 2 by hot pressing, obtained the maximum thermoelectric figure of merit ZT of 0.86 and 0.87 at about 590 and 715 K, respectively.…”

Transport properties of quaternary Ag–Bi–Sb–Te alloys prepared by pressureless sintering

“…The effectiveness of a material for thermoelectric applications is characterized by figure of merit Z, Z = a 2 r / j, where a, r, j are the Seebeck coefficient, electrical conductivity and thermal conductivity of the materials respectively. Bismuth telluride based alloys are known to be one of the current state-of-the-art thermoelectric materials used near room temperature, but interest in developing the materials with higher conversion efficiency has been increasing [1][2][3][4]. Jiang et al [5] and Jiang et al [6] prepared the grain-oriented p-type Bi -Sb -Te materials using spark plasma sintering (SPS) technique, and found that the maximum dimensionless thermoelectric figure of merit reached 1.15 at 350 K. Kurosaki et al [7] and Yamanaka et al [8] investigated p-type polycrystallinesintered materials Tl 9 BiTe 6 and TlSbTe 2 by hot pressing, and achieved the maximum ZT values of 0.86 at about 590 K and 0.87 at 715 K, respectively.…”

Non-equilibrium Phenomenon between Electron and Lattice Systems Induced by the Peltier Effect

“…However, the requirement, that the heat-flow must be constant because the thermal conductivity is material constant, is not always ensured by the results alone in ref. 3. Therefore, the conclusion of the non-linear temperature distribution has been still open.…”

“…(Bi,Sb) 2 Te 3 shows the clear nonlinear phenomenon. 3) It has relatively large electronic thermal conductivity and large thermoelectric power. Voltage terminals pairs are always set at the symmetrical positions to the center of the sample.…”

“…In the experiments, sufficient wait time is taken for each current direction to measure the voltage values in the stationary state. 2,3) The sample is slowly cooled down by the rate of $1 K/h during the measurements. All measurements have been made in the condition of small temperature differences below 150 mK by the applied dc current of I ¼ 500 mA.…”