High Thermoelectric Performance SnTe with a Segregated and Percolated Structure

A nanostructure has a significant role in enhancing the power factor and preventing the heat propagation for thermoelectric materials. Herein, we propose a unique segregated and percolated (SP) microphase-separated structure to enhance the thermoelectric performance of SnTe. The SP structure is composed of insoluble SnTe and AgCuTe, in which AgCuTe with ultralow lattice thermal conductivity undergoes a solid-phase welding during a spark plasma sintering process and forms continuous percolated layers at the interface of isolated SnTe. The SP structure achieved a simultaneous scattering for low energy holes due to the energy offset of the valence band maximum between SnTe and AgCuTe and for phonons due to the noncoherent interfaces between SnTe and AgCuTe, resulting in a high Seebeck coefficient of ∼219.4 μV/K and a low lattice thermal conductivity of ∼1.1 W m^-1 K^-1 at 800 K for (SnTe)_0.55(AgCuTe)_0.45. The thermoelectric performance was further enhanced by means of the cosubstitution of In and Mn for Sn in the SnTe lattice, inducing resonance levels and extra phonon scattering. As a result, the SP structure combined with In/Mn codoping enable us to achieve a low lattice thermal conductivity of 0.47 W m^-1 K^-1, a peak ZT of ∼1.45 at 800 K, and a high average ZT of ∼0.73 (400-800 K) for (Sn_0.98In_0.01Mn_0.01Te)_0.75(AgCuTe)_0.25.

Improved Thermoelectric Performance of P-type SnTe through Synergistic Engineering of Electronic and Phonon Transports

SnTe has been regarded as a potential alternative to PbTe in thermoelectrics because of its environmentally friendly features. However, it is a challenge to optimize its thermoelectric (TE) performance as it has an inherent high hole concentration (n_H∼2 × 10²⁰ cm^-3) and low mobility (μ_H∼18 cm² V^-1 s^-1) at room temperature (RT), arising from a high intrinsic Sn vacancy concentration and large energy separation between its light and heavy valence bands. Therefore, its TE figure of merit is only 0.38 at ∼900 K. Herein, both the electronic and phonon transports of SnTe were engineered by alloying species Ag_0.5Bi_0.5Se and ZnO in succession, thus increasing the Seebeck coefficient and, at the same time, reducing the thermal conductivity. As a result, the TE performance improves significantly with the peak ZT value of ∼1.2 at ∼870 K for the sample (SnGe_0.03Te)_0.9(Ag_0.5Bi_0.5Se)_0.1 + 1.0 wt % ZnO. This result proves that synergistic engineering of the electronic and phonon transports in SnTe is a good approach to improve its TE performance.

Ultralow dark current infrared photodetector based on SnTe quantum dots beyond 2 μm at room temperature

Quantum dots (QDs) are promising materials used for room temperature mid-infrared (MIR) photodetector due to their solution processing, compatibility with silicon and tunability of band structure. Up to now, HgTe QDs is the most widely studied material for MIR detection. However, photodetectors assembled with HgTe QDs usually work under cryogenic cooling to improve photoelectric performance, greatly limiting their application at room temperature. Here, less-toxic SnTe QDs were controllably synthesized with high crystallinity and uniformity. Through proper ligand exchange and annealing treatment, the photoconductive device assembled with SnTe QDs demonstrated ultralow dark current and broadband photo-electric response from visible light to 2 μm at room temperature. In addition, the visible and near infrared photo-electric performance of the SnTe QDs device were well maintained even standing 15 d in air. This excellent performance was due to the effective protection of the ligand on surface of the QDs and the effective transport of photo-carriers between the SnTe interparticles. It would provide a new idea for environmentally friendly mid-IR photodetectors working at room temperature.

Core-shell nanostructures introduce multiple potential barriers to enhance energy filtering for the improvement of the thermoelectric properties of SnTe

Using dispersed nanostructures to induce an energy filtering effect is an easy and effective mechanism to optimize the performance of bulk thermoelectric materials. Compared with other nanostructures, core-shell nanostructures possess more interfaces and multiple potential barriers, which would lead to a significant impact on the thermal and electrical properties of materials. In this paper, after BiCuSeO alloy doping into SnTe, SnO2 layers were formed at the interfaces and the BiCuSeO nanoparticles were wrapped in the SnO2 shell during the following high temperature solid state reaction. The formation of SnO2 layers could be observed and confirmed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). BiCuSeO@SnO2 core-shell nanostructures can introduce multiple potential barriers to enhance the energy filtering effect. Once the BiCuSeO doping concentration was over 3%, the carrier concentration could decrease to about 10% while the mobility increases to 350% compared to the values of the undoped sample at room temperature. Meanwhile, the Seebeck coefficients were improved to 176.05 μV K-1 at 835 K. Additionally, due to the scattering of core-shell nanostructures for the phonons, a lower thermal conductivity is achieved with a value of 1.04 W m-1 K-1 at 835 K in Sn1.03Te-5% BiCuSeO. Combined with the improvement of thermal and electrical properties by the BiCuSeO@SnO2 core-shell, a high ZT value of ∼1.21 was achieved for Sn1.03Te-5% BiCuSeO at 835 K, which was enhanced by 190% compared to pristine SnTe.

Enhancement of Thermoelectric Properties in Pd-In Co-Doped SnTe and Its Phase Transition Behavior

SnTe has attracted more and more attention due to the similar band and crystal structure with high performance thermoelectric materials PbTe. Here, we introduced Pd into SnTe and the valence band convergence was confirmed by first-principles calculation. In the experimental process, we found that Pd-doped SnTe exhibit a reduced thermal conductivity because of softening chemical bonds and grain refining effects. To further improve the thermoelectric performance, Pd-In codoped SnTe samples were prepared, and the abnormal change of thermal conductivity was observed. The results of synchrotron powder diffraction suggest that the local phase transition (local structural distortions) near 400 K results in the first turn on thermal conductivity. Similarly, the second local phase transition in near 600 K observed by neutron powder diffraction lead to a decrease thermal conductivity of the sample. Finally, a peak thermoelectric figure of merit (ZT) ≈ 1.51 has been obtained in Sn_0.98Pd_0.025In_0.025Te at 800 K.

Room Temperature Mid-IR Detection through Localized Surface Vibrational States of SnTe Nanocrystals

Quantum dots (QDs) are now well established as promising materials for room temperature mid-infrared (MIR) detection beyond 3 μm. Here, we have replaced commonly reported mercury based quantum dots with less toxic SnTe and PbSnTe. Inverse MIR detection at room temperature is demonstrated with planar, solution, and air-processed PbSnTe and SnTe QD devices. The detection mechanism is shown to be mediated by an interaction between MIR radiation and the vibrational stretches of adsorbed hydroxyl species. Devices are shown to possess mA/W responsivity via a reduction in conductance due to MIR irradiation and, unlike classic MIR photoconductors, are unaffected by visible wavelengths. As such, these devices offer the possibility of MIR thermal imaging that has an intrinsic solution to the blinding caused by higher energy light sources.

Enhanced thermopower in rock-salt SnTe–CdTe from band convergence

The rock-salt type SnTe–CdTe alloys have been synthesized by the zone-melting method and show enhanced thermoelectric performance due to the improved band convergence.