Weak electron–phonon coupling contributing to high thermoelectric performance in n-type PbSe

Abstract

PbSe is a surprisingly good thermoelectric material due, in part, to its low thermal conductivity that had been overestimated in earlier measurements. The thermoelectric figure of merit, zT, can exceed 1 at high temperatures in both p-type and n-type PbSe, similar to that found in PbTe. While the p-type lead chalcogenides (PbSe and PbTe) benefit from the high valley degeneracy (12 or more at high temperature) of the valence band, the n-type versions are limited to a valley degeneracy of 4 in the conduction band. Yet the n-type lead chalcogenides achieve a zT nearly as high as the p-type lead chalcogenides. This effect can be attributed to the weaker electron-phonon coupling (lower deformation potential coefficient) in the conduction band as compared with that in the valence band, which leads to higher mobility of electrons compared to that of holes. This study of PbSe illustrates the importance of the deformation potential coefficient of the charge-carrying band as one of several key parameters to consider for band structure engineering and the search for high performance thermoelectric materials.energy | semiconductor | quality factor W aste heat recovery using thermoelectric power generation is attracting considerable interest from the automobile industry (1) as well as from many other areas (2). Large-scale production of bulk materials with high figure of merit, zT, defined as zT ¼ S 2 σT∕ðκ e þ κ L Þ (S is the Seebeck coefficient, σ is the electric conductivity, and κ e and κ L are the electronic and lattice thermal conductivity, respectively), is the key to widespread adaption of thermoelectric technology. The search for good thermoelectric materials has focused on investigating semiconductors that have suitable band structures and low thermal conductivities (3, 4). As one of the first investigated material systems (5), PbTe and its alloys have been extensively studied and remain some of the best (6, 7) thermoelectric materials for applications from 500 to 900 K. Considerable effort has been made to achieve a higher zT in these alloys by reducing the lattice thermal conductivity, κ L , by incorporation of nanometer scale inclusions (8-11). Other strategies approach the challenge of increasing zT from different angles, such as band structure distortion by Tl doping (12), and more recently, increasing band degeneracy by converging two different valence bands in p-type PbTe (13).It can be shown that the material parameter called the thermoelectric quality factor, B,determines the optimized figure of merit (14-16) (N V is the band degeneracy, m à b is the density of states effective mass of a single band, μ 0 is the mobility at nondegenerate limit, and κ L is the lattice thermal conductivity). This expression is derived for semiconductors with single band transport behavior where the carrier concentration can be optimized to achieve maximum zT. For good thermoelectric semiconductors the dominant scattering mechanism at high temperatures, where zT peaks, is typically due to acoustic phonons. The deformation pote...

Enhancement of thermoelectric performance in n-type PbTe1−Se by doping Cr and tuning Te:Se ratio

“…However, this composition is less susceptible to bipolar conduction and the bipolar temperature is higher than that of the Te-rich composition. This is due to the suppression of minority carriers by the band gap increase in the Se-rich composition with increasing temperature consistent with the previous studies [31]. The electrical conductivity also follows a similar trend as the Te-rich composition in such a way that it increased when the Cr concentration increased to a critical value of 1.5 atm.…”

Nanoporous PbSe–SiO2 Thermoelectric Composites

“…Around RT, the κ L decreases from 1.6 W m −1 K −1 to an average value of 1.3 W m −1 K −1 as SiO 2 was incorporated. As temperature increases, κ L decreases very quickly, downward to a plateau around 0.6 W m −1 K −1 before 600 K for most SiO 2 ‐contained samples, which is much smaller than the average κ L value of 0.8 W m −1 K −1 at 700–800 K for PbSe bulks 32, 33. The sharp decrease and the lower κ L values are considered associated with the SiO 2 addition, probably with multiple effects from the abundant nanopores, interfaces, refined grains and SiO 2 nanoparticles.…”

Low Sound Velocity Contributing to the High Thermoelectric Performance of Ag8SnSe6

“…Interestingly, both m* and E def are found to be independent of temperature and doping concentration, indicating a rigid band behavior for Ag 8 Sn 1− x Nb x Se 6 . Not only an m* of 0.2 m e ( m e is the free electron mass) but also an E def of ≈25 eV falls in a typical range for thermoelectric semiconductors 8, 35, 37, 41, 42…”