Pure SnTe Research Articles

Nanocrystal-based thermoelectric SnTe-NaSbSe2 alloys with strengthened band convergence and reduced thermal conductivity

Ternary I-V-VI2 colloidal NaSbSe2 nanocrystals are herein used to improve the performance of lead-free SnTe thermoelectric materials. We showcase a versatile bottom-up engineering approach to produce nanocrystal-based SnTe-NaSbSe2 alloys from the rapid hot press of colloidal nanocrystal building blocks. The incorporation of NaSbSe2 nanocrystals significantly enhances the Seebeck coefficient of SnTe. The band convergence and simultaneous increasing band gap of SnTe-NaSbSe2 alloys are certified by the first-principles density functional theory calculations. Besides, defect engineering generated by the incorporation of NaSbSe2 nanocrystals such as Sn vacancies, substitution point defects, dense dislocations, and strains generated by the NaSbSe2 nanoparticles incorporation result in a dramatic reduction of the lattice thermal conductivity below the amorphous limit of pure SnTe, down to 0.38 W m−1 K−1. As a consequence, power factors enhance up to 1.77 mW m−1 K−2, which is ∼193 % higher than that of the pristine SnTe, and thermoelectric figures of merit up to 1.15 at 823 K for (SnTe)0.85(NaSbSe2)0.15 are achieved.

Dilute Sc/Y doping in SnTe for efficient charge transport modulation and high thermoelectric performance

As a highly potential environmental-friendly medium-temperature thermoelectric material, pure SnTe exhibits relatively poor performance due to its intrinsic high carrier concentration and large energy offset between the two valence bands. In the present work, dilute Sc/Y doping is innovatively adopted to synergistically decrease carrier concentration and achieve strong band convergence. The Hall measurement results indicate that 3 % Y doping realizes the lowest carrier concentration of 2.6 × 1019 cm−3 in SnTe. Sc and Y have similar effects in promoting band convergence, with their effects second only to toxic Hg elements at the same doping concentration. The effective decoupling of electrical and thermal transport parameters results in a high average ZT of 0.453 for Sn0.975Sc0.025Te sample, which is 103 % higher than that of pure SnTe. In addition, with Li2Te alloying to regulate carrier concentration, high-performance temperature range could be adjusted, which is more conducive to dealing with different temperature scenarios. The role of Sc/Y doping disclosed in this work provides more options for further improving the performance of SnTe-based materials.

Enhanced thermoelectric performance of P-type SnTe thin film through Sr doping and Post-Annealing treatment

Lead-free tin telluride (SnTe) has gained significant attention for its potential use in mid-temperature thermoelectric power generation. In this work, we systematically analyzed the thermoelectric power factor of Sn0.7Sr0.3Te thin films at various post-annealing temperatures through structural, morphological, and thermoelectric property measurements. Our findings show that Sr-doping in the SnTe thin film matrix and post-annealing treatment can significantly enhance the thermoelectric properties by modifying the band structure and introducing an energy-filtering effect at grain boundaries. We achieved a maximum power factor of 29.4 μWm-1K−2 at 523 K for Sn0.7Sr0.3Te thin films post-annealed at 1073 K, which is three times greater than that of pure SnTe. This work demonstrates that Sr-doping and post-annealing effects can tune the band gap, induce band degeneration, and reduce grain size, resulting in a high thermoelectric power factor of the SnTe thin film.

Highly Stable Metal─Na0.02Pb0.98Te Contacts for Medium Temperature Thermoelectric Devices.

In the medium temperature (600-850 K) range, Na0.02Pb0.98Te is a highly efficient p-type thermoelectric compound. Device fabrication utilizing this compound for power generation demands highly stable low-contact resistance contacts with metal electrodes. This work investigates the microstructural, electrical, mechanical, and thermochemical stability of Na0.02Pb0.98Te-metal (Ni, Fe, and Co) contacts made by a one-step vacuum hot pressing process. Direct contact mostly resulted in either an interface with poor mechanical integrity, as in Co and Fe, or poisoning of the TE compound, as in the case of Ni, which results in high specific contact resistance (rc). In Ni and Co, adding a SnTe interlayer lowers the rc and strengthens the contact. It does not, however, effectively stop Ni from diffusing into Na0.02Pb0.98Te. The bonding is poor in the Fe/SnTe/Na0.02Pb0.98Te contacts due to the absence of any reaction at the Fe/SnTe interface. A composite buffer layer Co + 75 vol % SnTe with SnTe improves the mechanical stability of the Co contact with moderately lesser rc than pure SnTe alone. However, a similar approach with Fe does not yield stable contact. The Co/Co + 75 vol % SnTe/SnTe/Na0.02Pb0.98Te contact exhibits rc less than 50 μΩ cm2 and has good microstructural and mechanical stability after annealing at 723 K for 170 h.

Structural, electronic and thermoelectric properties of SnTe with dilute co-doping of Ag and Cu

The low bandgap semiconductor, SnTe is receiving significant attention as a thermoelectric material because of its low toxicity and environment-friendly nature. In this study, we report the effect of co-doping dilute concentrations of Ag and Cu ions in SnTe that suppresses the Sn vacancies leading to optimized thermoelectric properties. Samples of nominal chemical composition Sn1.03–2xAgxCuxTe (x = 0, 0.01, 0.02, 0.04) were prepared by the solid-state route. The Rietveld refinement of powder XRD of these compounds showed a fcc (Fm3¯m) structure with no other impurity phases. Diffuse reflectance IR spectroscopy showed an increase in the bandgap upon Ag-Cu co-doping in SnTe, associated with valence band convergence. Electronic band structure calculations confirmed an increase in the bandgap along with a reduction in the energy difference between light and heavy valence bands having maxima at the L and Σ points. Partial density of states (P-DOS) calculations showed that Ag-Cu doping in SnTe does not contribute towards the formation of resonant energy levels. The Seebeck coefficient S of the Sn1.01Ag0.01Cu0.01Te reached a maximum value of ∼ 95 μV/K at 783 K, compared to 86 μV/K of pure SnTe. The power factor increased with the doping concentration, reaching ∼ 10.8 μWK−2cm−1 at 783 K for x = 0.04. The lattice thermal conductivity κL decreased on Ag-Cu co-doping, with κL = 0.44 Wm−1K−1 above 750 K for x = 0.04, which is close to the Cahill model. The combination of higher power factor and reduced lattice thermal conductivity in the Ag-Cu co-doped samples resulted in enhanced ZT = 0.24–0.29 at 773 K.

Nanoarchitectonics of tin telluride: A novel pseudocapacitive material for energy storage application

In this study, we presented the synthesis of tin telluride (SnTe) nanoparticles and reduce graphene oxide mixed with SnTe (rGO/SnTe) nanocomposite through the hydrothermal technique. The rGO with various contents (0, 5 and 10%) has been added in SnTe and nominated as ST, STG-1 and STG-2 respectively for electrode materials of supercapacitor. The prepared materials were characterized using X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, Field emission scanning electron microscopy (FESEM), Cyclic voltammetry (CV), Charging/discharging (GCD) and Brunauer–Emmett–Teller (BET) analysis. XRD patterns approve SnTe form a cubic crystal phase. Based on the FTIR results Sn–Te vibration modes was observed in pure SnTe and in rGO/SnTe composite some vibration mode were disappeared at 10% rGO content. FESEM study presences samples exhibit spherical like shapes morphology with wide space and the average grain size is in between 45 and 32 nm. EDX analysis confirm the stoichiometry of the electrode materials. The specific capacitance (SC) for SnTe electrode 623 Fg-1 rises to 1316 Fg-1 with 10% rGO/SnTe nanocomposite, which specifies that rGO has improved the electrochemical characteristics of SnTe nanoparticles. The rGO/SnTe nanocomposite electrode has the highest specific energy density and specific power density value of 16 Wh/kg and 3748 W/kg, respectively with columbic efficiency retention is 92.2% after 1000 cycles. These outcomes collectively indication that SnTe/rGO nanocomposite have extensive application prospects.

Synergistic band modulation and precipitates: Achieving high quality factor in SnTe

Breaking the thermoelectric figure of merit zT barrier of SnTe enables it to become a promising alternative to PbTe; however, the inferior and strongly coupled physicochemical properties of pristine SnTe severely restrict the efficient optimization. Herein, we doped trivalent Sb in SnTe and incorporated SnS particles to achieve high quality factor B through a two-step optimization strategy of tuning the valence band structure and intercalating heterostructural precipitates, and well predicted the potential prospects. The high solubility limit of Sb not only reduced the carrier concentration nH but also significantly optimized the valence band structure and improved the Seebeck coefficient, thereby enhancing the weight mobility μw in the all-temperature region. Furthermore, the additional SnS, which tends to exist as precipitates with different micrometer-scale sizes, enhanced low-medium-frequency phonon scattering in a wider frequency range except for point defects scattering, suppressing the lattice thermal conductivity to 0.55 W m−1 K−1. As a result of this synergistic effect, a high B-factor of ∼0.82 greater than triple pure SnTe was obtained in Sn0.91Sb0.09Te-10%SnS, with an enhanced zT of ∼1.15 at 850 K. More importantly, the high B-factor accurately predicted an excellent zT value of ∼1.65 at the optimal Fermi level, which highlights the great potential of Sn1-xSbxTe-y%SnS-based materials. This work provides an effective route for stepwise optimization of electrical and thermal performance from the B-factor perspective and has guiding significance for other thermoelectric materials.

To Love and to Kill: Accurate and Selective Colorimetry for Both Chloride and Mercury Ions Regulated by Electro-Synthesized Oxidase-like SnTe Nanobelts

Herein, SnTe nanobelts (NBs) with efficient oxidase-mimetic activity were synthesized by the simple electrochemical exfoliation method. A specific inhibition effect of Cl- on the enzymatic behavior of the pure SnTe NBs was discovered, which was accordingly used for establishing a highly feasible, sensitive, selective, and stable Cl- colorimetric assay. The detection concentration range was 50 nM to 1 mM, and the lowest detection limit was 20 nM for Cl-. In addition, a signal on-off-on route based on the SnTe NB nanozyme was designed to realize the reliable and specific detection of Hg2+. Therein, the SnTe NBs were grafted with gold nanoparticles to form a hybrid of SnTe/Au, resulting in the depression of the oxidase-like activity, which can then be recovered in the presence of the Hg2+ due to the formation of a gold amalgam. Especially, it was found that the high concentration of Cl- over 3 mM could again exert suppression influence toward the enzymatic activity of the SnTe/Au-Hg system. Based on the to-love-and-to-kill interaction between Cl- and Hg2+, the detection range for Cl- can be extended to 40 to 250 mM. In return, the assays of Cl- could avoid in advance its interference toward the accurate Hg2+ assays. We systematically clarified the oxidase-like catalytic mechanism of the SnTe-derived nanozyme systems. The as-proposed colorimetry can be successfully applied in practical samples including the sweat, human serum, or seawater/tap water, relating to cystic fibrosis, hyper-/hypochloremia, or environmental control, respectively.

Ultralow thermal conductivity and enhanced thermoelectric properties of SnTe based alloys prepared by melt spinning technique

Abstract SnTe based materials have attracted considerable attention owing to their eco-friendly nature. Here, we employed a melt spinning method combined with spark plasma sintering (MS-SPS) technique to optimize the electrical and thermal transport performance of SnTe based alloys. Doping with Sb optimizes carrier concentration efficiently, leading to an enhanced Seebeck coefficient and power factor. Unlike the original phonon dispersion relation, the introduction of Sb heightens the phonon-phonon interaction and flattens the phonon dispersion, resulting in a significant decline in the phonon group velocity. Combined with the enhanced scattering from lattice distortion, nanoprecipitates and large amounts of grain boundaries, an ultralow lattice thermal conductivity of 0.57 Wm−1K−1 was obtained for Sn0.91Sb0.18Te1.18 MS-SPS alloy. An improved ZT value of 0.95 can be realized, which is 2.2 times higher than that of pure SnTe alloy. The enhanced phonon scattering and reinforced phonon-phonon interaction give valuable access to develop high-performance SnTe based thermoelectric materials.

Microstructure and enhanced thermoelectric performance of Te–SnTe eutectic composites with self-assembled rod and lamellar morphology

The eutectic Te–SnTe composites with self-organized rod and lamellar structure were synthesized using the directional solidification technology. The experiments show that the volume fraction and shape-tunable morphology of the SnTe phase vary with the alloy compositions. The thermoelectric properties of the composites are dependent on the volume fraction of SnTe phase and exhibit obvious anisotropy in different growth directions. The composites perpendicular to the growth direction possess much larger S and lower κL than that in the parallel direction. High resolution transmission electron microscopy (HRTEM) results illustrate that there are a given amount of dislocations and atomic mismatch stress field around the Te–SnTe eutectic interface areas, which effectively scatter the heat-carrying phonons, leading to an ultralow lattice thermal conductivity of 0.64 Wm−1K−1 for Sn-80at%Te eutectic alloy. The obtained maximum figure of merit is 0.40 for Sn-90at%Te alloy which is 1.5–1.9 times higher than that of pure SnTe and Te, respectively. It demonstrates that introducing large amounts of eutectic interfaces in Te–SnTe composites is an effective way to enhance the thermoelectric performance.

Thermoelectric SnTe with Band Convergence, Dense Dislocations, and Interstitials through Sn Self-Compensation and Mn Alloying.

SnTe is known as an eco-friendly analogue of PbTe without toxic elements. However, the application potentials of pure SnTe are limited because of its high hole carrier concentration derived from intrinsic Sn vacancies, which lead to a high electrical thermal conductivity and low Seebeck coefficient. In this study, Sn self-compensation and Mn alloying could significantly improve the Seebeck coefficients in the whole temperature range through simultaneous carrier concentration optimization and band engineering, thereby leading to a large improvement of the power factors. Combining precipitates and atomic-scale interstitials due to Mn alloying with dense dislocations induced by long time annealing, the lattice thermal conductivity is drastically reduced. As a result, an enhanced figure of merit (ZT) of 1.35 is achieved for the composition of Sn0.94 Mn0.09 Te at 873 K and the ZTave from 300 to 873 K is boosted to 0.78, which is of great significance for practical application. Hitherto, the ZTmax and ZTave of this work are the highest values among all single-element-doped SnTe systems.

Strategy to optimize the overall thermoelectric properties of SnTe via compositing with its property-counter CuInTe2

SnTe, a lead-free analogue of PbTe, exhibits inferior thermoelectric performance due to its intrinsically high carrier concentration, and thus too low Seebeck coefficient and high thermal conductivity. To optimize the overall properties of SnTe, we composited SnTe with the other compound with opposite performance. CuInTe2 is a good choice due to its low carrier concentration, high Seebeck coefficient and relatively low thermal conductivity. As a result, the most optimized properties can be obtained in CuSnmInTem+2 when m = 7, and an enhanced figure of merit ZT can be obtained, ∼1.0 at 873 K, which is a three-fold increase for pure CuInTe2 and one-fold increase for pure SnTe. The overall properties are optimized much greater than the expectation, which was estimated through Effective Medium Theory (EMT). Such deviation can be ascribed to the existence of high density of coherent nanostructures.

Ultralow Lattice Thermal Conductivity and Enhanced Thermoelectric Performance in SnTe:Ga Materials

Ultralow thermal conductivity is of great interest in a variety of fields, including thermoelectric energy conversion. We report, for the first time, experimental evidence that Ga-doping in SnTe may lower the lattice thermal conduction slightly below the theoretical amorphous minimum at high temperature. Such an effect is justified by the spontaneous formation of nanoprecipitates we characterized as GaTe. Remarkably, the introduction of Ga (2–10%) in SnTe also improves the electronic transport properties by activating several hole pockets in the multivalley valence band. Experimental results are supported by density functional theory calculations. The thermoelectric figure of merit, ZT, reaches ∼1 at 873 K in Sn0.96Ga0.07Te, which corresponds to an ∼80% improvement with respect to pure SnTe.

Valence Band Modification and High Thermoelectric Performance in SnTe Heavily Alloyed with MnTe.

We demonstrate a high solubility limit of >9 mol% for MnTe alloying in SnTe. The electrical conductivity of SnTe decreases gradually while the Seebeck coefficient increases remarkably with increasing MnTe content, leading to enhanced power factors. The room-temperature Seebeck coefficients of Mn-doped SnTe are significantly higher than those predicted by theoretical Pisarenko plots for pure SnTe, indicating a modified band structure. The high-temperature Hall data of Sn1-xMnxTe show strong temperature dependence, suggestive of a two-valence-band conduction behavior. Moreover, the peak temperature of the Hall plot of Sn1-xMnxTe shifts toward lower temperature as MnTe content is increased, which is clear evidence of decreased energy separation (band convergence) between the two valence bands. The first-principles electronic structure calculations based on density functional theory also support this point. The higher doping fraction (>9%) of Mn in comparison with ∼3% for Cd and Hg in SnTe gives rise to a much better valence band convergence that is responsible for the observed highest Seebeck coefficient of ∼230 μV/K at 900 K. The high doping fraction of Mn in SnTe also creates stronger point defect scattering, which when combined with ubiquitous endotaxial MnTe nanostructures when the solubility of Mn is exceeded scatters a wide spectrum of phonons for a low lattice thermal conductivity of 0.9 W m(-1) K(-1) at 800 K. The synergistic role that Mn plays in regulating the electron and phonon transport of SnTe yields a high thermoelectric figure of merit of 1.3 at 900 K.

Facile precipitation of two phase alloys in SnTe0.75Se0.25 with improved power factor

Abstract Multiphase thermoelectric (TE) materials have received great interest in recent years due to the synergistic improvements in TE properties. We report for the first time on melt spun samples with nominal composition of SnTe0.75Se0.25. Interestingly, an orthorhombic second phase was observed to exhibit change in microstructure under low applied pressure – the metastable nature leads to an observed increase in mass fraction with increased applied pressure – and this second phase can be stabilized by concurrent application of heat and pressure during hot pressing. The second phase reduces electrical resistivity, while increasing Seebeck coefficient values slightly, especially at higher temperatures. A peak power factor of 1.3 mW/m K2 is obtained at 494 K, which is a 1.5 times enhancement over the peak power factor of pure SnTe. The peak ZT achieved for the alloy is 0.19 at 548 K, which is three times that of pure SnTe.

The state of 57Fe in pure and oxidized tin chalcogenides by Mössbauer spectroscopy

A Mössbauer spectroscopy study has been made of the stabilization states of 57Fe in pure tin chalcogenides. The values of the isomer shifts and the quadrupole splittings lead to the conclusion that iron presents the electronic configuration 3 d 54 s x at high spin in the interstitial position. This result is confirmed varying the 57Fe neighbours by partial substitution of tellurium with oxygen. In this case, too, the values of Mössbauer parameters confirm the same results. The quadrupole moment present in pure SnTe doped 57Co, and the shift of isomer shift towards less positive values for the oxidizated samples have been qualitatively justified as well.

Annealing studies of PbTe and Pb1−xSnxTe

The results of single-zone annealing of 76 samples of Pb1−xSnxTe are reported, covering the entire composition range from pure PbTe to pure SnTe. Some of the sample preparation work overlapped and improved on the work of others, while some of the results, particularly in the alloy samples, are new. Annealing times, temperatures, source ingot preparation, resulting carrier concentrations, and 77 °K Hall mobilities are reported. The Knight shift of the Pb207 nuclear magnetic resonance and the NMR line shape were used for additional sample characterization. This interesting technique was applied most successfully in the pure PbTe samples with carrier concentrations below 1018 cm−3. It was discovered from NMR studies on powders that strain damage introduced by powdering could completely compensate p-type PbTe. No corresponding effect was noted in n-type PbTe, suggesting the presence of damage-induced levels in the gap.

Electron energy loss spectra of GeTe-SnTe alloys

Abstract Electron energy loss spectra have been recorded from films of epitaxially grown GeTe-SnTe semiconducting pseudo-binary alloys using an energy-analysing electron microscope. The plasmon energy varied between (16·1±0·1) ev for pure GeTe and (14·8±0·1) ev for pure SnTe; the plasmon energy of the GeTe-SnTe alloys varied as n ½, where n is the free-electron density of the material. The results of calibration experiments have been used to identify small regions in GeTe alloys annealed at a temperature ∼ 250°C in the electron microscope. Because of the small size of the regions examined, and the difficulties in interpreting the complex diffraction patterns recorded from them, the composition of the annealed alloys could be determined only by energy-analysing electron microscopy.