Discordant Gd and Electronic Band Flattening Synergistically Induce High Thermoelectric Performance in n-type PbTe

Abstract

p-type PbTe is the most sought-after material in thermoelectrics due to its ultrahigh thermoelectric figure of merit (zT), but the performance of n-type PbTe lags behind due to the simplicity of its conduction band compared to those of rich valence bands. Here, we have synergistically enhanced the Seebeck coefficient and lowered the lattice thermal conductivity of n-type PbTe by Gd doping, which resulted in high thermoelectric performance. Gd doping in PbTe enhances the electron effective mass via flattening of the conduction band, which significantly improves the Seebeck coefficient. Gd is found to remain in an off-centered position inside the rock-salt PbTe lattice, which increased the lattice anharmonicity. Density functional perturbation theory (DFPT) calculations indicate that Gd induces a low energy nearly flat optical phonon mode that drastically increases the phonon scattering rate and lowers lattice thermal conductivity to 0.78 W/(m K). As a result, we achieved a high zT of 1.65 at 678 K for Pb 1−x Gd x Te 1−y I y (x = 0.33%, y = 1%).

Emphanisis in Cubic (SnSe)0.5(AgSbSe2)0.5: Dynamical Off-Centering of Anion Leads to Low Thermal Conductivity and High Thermoelectric Performance

“…Typically, the structural transformation occurs from a low symmetric ground state to a higher symmetry state upon heating . This happens because as the temperature increases, the system favors a more disordered state, i.e., a high symmetric phase. , However, recently it has been observed in few high symmetric inorganic solids the formation of locally broken asymmetric phases upon warming, an unusual phenomenon termed “ emphanisis ”. − Emphanisis means transformation of a high symmetric structure to a lower symmetric structure with warming, which is driven largely by the presence of stereochemically active lone pair of electrons as seen in the case for IV–VI chalcogenides like PbQ (Q = S, Se, Te) ,, and SnTe or in perovskite halides like CsSnBr 3 , etc. , Such local off-centering of atoms creates multiple short and long bonds in its local environment, thereby inducing a local aperiodicity that impedes the phonon propagation, thus leading to low lattice thermal conductivity (κ lat ). − …”

Enhancing Thermoelectrics for Small-Bandwidth n-Type PbTe–MnTe Alloys via Balancing Compromise

“…Due to the symmetry crystal structure and large lattice anharmonicity, lead chalcogenide PbTe is widely utilized as a thermoelectric material in the medium-temperature region (500–900 K). , This inspires numerous efforts to improve the peak and average thermoelectric figures of merit of n-type PbTe materials to achieve a higher conversion efficiency. − However, the thermoelectric parameters are strongly coupled with each other, the compromise between carrier concentration and Seebeck coefficient ( n / S ), − the trade-off between effective mass and carrier mobility (μ/ m b * ), − even the only relatively independent parameter, and the lattice thermal conductivity, also contradictory to the carrier mobility (μ/κ l ), , which make it challenging to obtain the net enhancement of zT. Therefore, the solution of the aforementioned compromises among the thermoelectric parameters is of significance and necessary.…”

Local ferroelectric polarization switching driven by nanoscale distortions in thermoelectric $${\text {Sn}}_{0.7}{\text {Ge}}_{0.3}{\text {Te}}$$

“…The presence of such local off-centering has benefited the thermoelectric performance of many compounds by lowering their 29 – 32 . In particularly, the local off-centering of cations are found to exist till the measured temperature of (600 K).…”