Abstract
We investigated the thermoelectric properties of the Pb0.75Sn0.25Se and Pb0.79Sn0.25Se1−xClx (x = 0.0, 0.2, 0.3, 0.5, 1.0, 2.0 mol.%) compounds, synthesized by hot-press sintering. The electrical transport properties showed that low concentration doping of Cl (below 0.3 mol.%) in the Pb-excess (Pb,Sn)Se samples increased the carrier concentration and the Hall mobility by the increase of carriers’ mean free path. The effective mass of the carrier was also enhanced from the measurements of the Seebeck coefficient. The enhanced effective masses of the carrier by the Cl-doping can be understood by the enhanced electron-phonon interaction, caused by the crystalline mirror symmetry breaking. The significantly decreased lattice thermal conductivities showed that the crystalline mirror symmetry breaking decreased the lattice thermal conductivity of the Pb-excess (Pb,Sn)Se. By the Cl-doping and the Pb-excess’s synergistic effect, which can suppress the bipolar effect, the zT values of x = 0.2 and 0.3 mol.% reached 0.8 at 773 K. Therefore, we suggest that Pb-excess and the crystalline mirror symmetry breaking by Cl-doping are effective for high thermoelectric performance in the (Pb,Sn)Se.
Highlights
Thermoelectric devices based on the Seebeck, Peltier, and Thomson effects can be used for thermoelectric power generation or solid-state cooling, including flexible or wearable thermoelectric devices [1,2]
The thermoelectric performance of the device is mainly determined by the dimensionless thermoelectric figure of merit, which is defined by zT = S2σT/κ, where S, σ, T, and κ are the Seebeck coefficient, electrical conductivity, absolute temperature, and thermal conductivity, respectively
The electrical resistivity and the Hall carrier concentration results clearly show that the Cl-doping in the Pb-excess (Pb,Sn)Se samples can increase the carrier concentration
Summary
Thermoelectric devices based on the Seebeck, Peltier, and Thomson effects can be used for thermoelectric power generation or solid-state cooling, including flexible or wearable thermoelectric devices [1,2]. The theoretical calculation shows that the breaking of the TCI state by lowering crystal symmetry can increase the thermoelectric power factor [8]. Nadoping in the TCI Pb0.6Sn0.4Te shows the enhancement of thermoelectric performance by the crystalline mirror symmetry breaking with the increased bandgap from ~0.1 to~0.22 eV, as well as the optimization of the carrier concentration [12]. The Pb excess in the PbSe can increase the thermoelectric performance of the n-type PbSe by decreasing the intrinsic defects, which can cause the generation of hole carriers [14]. The Cl-doping can increase the Seebeck coefficient by the enhanced effective mass of the carrier with the increase of the electronic bandgap [13], and the non-stoichiometric Pb addition can reduce the intrinsic defects of the PbSe [14]. We present the Cl-doping and Pb-excess’s synergistic effect in (Pb,Sn)Se toward high thermoelectric performance
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