SnTe Matrix Research Articles

Understanding the Chemical Nature of the Buried Nanostructures in Low Thermal Conductive Sb-Doped SnTe by Variable-Energy Photoelectron Spectroscopy

Nanoprecipitates embedded in a matrix of thermoelectric materials decrease the lattice thermal conductivity significantly by extensive heat carrying phonon scattering. Recently, two-dimensional layered intergrowth nanostructures of SnmSb2nTe3n+m embedded in SnTe matrix have provided record low lattice thermal conductivity in SnTe, but an understanding of the chemical nature of these layered nanostructures is still not clear. Herein, we studied the chemical nature of the intergrowth nanostructures of a series Sb-doped SnTe by variable-energy X-ray photoelectron spectroscopy at synchrotron, which is well known to probe buried interfaces and embedded nanostructures. The primary oxidation states of Sb, Sn, and Te in these intergrowth structures are found to be in +3, +2, and −2, respectively, which is expected from the composition. However, both the Sn and Sb are found to be slightly oxidized in the surface. From the intensity variation with photon energy, we have found a thin layer of SnO2 (∼4.5 nm) on the s...

Enhancing Thermoelectric Properties of InTe Nanoprecipitate-Embedded Sn1–xInxTe Microcrystals through Anharmonicity and Strain Engineering

As one of Pb-free thermoelectric materials, tin telluride (SnTe) has received extensive attention. Here, we report InTe nanoprecipi-tates embedded Sn1-xInxTe microcrystals with an improved thermoelectric performance prepared via a facile solvothermal method. In dopants can strikingly enhance the room-temperature thermopower from ~ 23 μV K-1 to ~ 88 μV K-1, which is attributed to the distortion of density of states near the Fermi level in the valence band of Sn1-xInxTe. Our detailed structural characterizations indi-cate that point defects, anharmonic-bonding, dislocations and strain around nanoprecipitates can effectively strengthen phonon scattering, and in turn significantly reduce lattice thermal conductivity. Raman spectroscopy analysis shows that optical phonon modes shifts toward higher wavenumber, indicating the change of the bonding force and the chemical environment in the system, which facilitates additional resistance to propagate heat carrying phonons. Finally, a high power factor of ~ 21.8 μW cm-1 K-2 and a corresponding figure of merit, ZT of ~ 0.78 are obtained in Sn0.99In0.01Te at 773 K. This study explores the fundamental In-doping mechanisms in a SnTe matrix, and demonstrates anharmonicity and strain engineering as effective approaches to boosting thermoe-lectric performance, which provides a new avenue in achieving high-performance thermoelectric properties of materials.

Enhancing thermoelectric performance of SnTe via stepwisely optimizing electrical and thermal transport properties

In this work, we report that the high performance of SnTe could be realized by enhancing electrical transport properties (power factor) and reducing thermal conductivity through stepwisely introducing elements of Sb, In and Se. We found that Sb and In co-doping can enhance Seebeck coefficients in the broad temperature range via optimizing carrier density and introducing resonant state, respectively. Moreover, nanostructures could be formed when the Sb content beyond the solubility limit in SnTe matrix, which coupled with point defects from In and Se alloying result in a very low (lattice) thermal conductivity through the enhanced phonon scattering from defects and grain boundaries. A peak ZT ∼1.0 at 923 K can be achieved with the enhanced power factor and reduced thermal conductivity. Accordingly, the average ZT value increases from ∼0.20 for undoped SnTe to ∼ 0.60 for multiple-doped SnTe (Sn0.823Sb0.17In0.007Te0.98Se0.02) over 300–923 K, generating a high calculated conversion efficiency ∼ 11%. Present results indicate the high performance of SnTe can be obtained through stepwisely optimizing strategy in both electrical and thermal transport properties.

Thermoelectric performance of SnTe with ZnO carrier compensation, energy filtering, and multiscale phonon scattering

AbstractIn this work, the thermoelectric properties of SnTe have been regulated synergistically by introduction of n‐type ZnO nanoinclusions. On one hand, the excessive holes in SnTe matrix were compensated properly by n‐type ZnO, and the Seebeck coefficient has been improved greatly due to the carrier energy filtering effect by a large quantity of ZnO‐SnTe hetero‐junction interface barriers; On the other hand, the thermal conductivity gets reduced by the enhanced phonon scattering from multiscale hierarchical architectures. Consequently, a maximum ZT of ~0.9 at 873K has been obtained in the 0.8 wt% sample, which enhances by 112% in comparison with the nanoinclusion‐free sample.

The origin of low thermal conductivity in Sn1−xSbxTe: phonon scattering via layered intergrowth nanostructures

The spontaneous formation of nanodomains of the Sb-rich layered intergrowth SnmSb2nTe3n+m compounds in a SnTe matrix resulted in ultralow lattice thermal conductivity.

High Thermoelectric Performance SnTe–In2Te3 Solid Solutions Enabled by Resonant Levels and Strong Vacancy Phonon Scattering

Herein, we report a significantly improved thermoelectric figure of merit ZT of ∼1.1 at ∼923 K in p-type SnTe through In2Te3 alloying and iodine doping. We propose that the introduction of indium at Sn sites in SnTe creates resonant levels inside the valence bands, thereby considerably increasing the Seebeck coefficients and power factors in the low-to-middle temperature range. Unlike SnTe–InTe, the SnTe–In2Te3 system displays much lower lattice thermal conductivity. Utilizing a model for point defect scattering, we analyze the origin of the low thermal conductivity in SnTe–In2Te3 and attribute it mainly to the strong vacancy originated phonon scattering between Sn atoms and the vacancies introduced by In2Te3 alloying and partly to the interfacial scattering by In-rich nanoprecipitates present in SnTe matrix. By alloying only In2Te3 with SnTe, a ZT value of ∼0.9 at 923 K was achieved. ZT can be further increased to ∼1.1 at 923 K through adjusting the charge carriers by iodine doping at Te sites.

Mn–Te bond in the rocksalt Sn 1− xMn xTe alloys and octahedral radius of Mn: X-Ray absorption- and diffraction study

The studies of local atomic structure in Sn 1− x Mn x Te ( x<0.07) alloys, with an attention to the nature of Mn–Te bond, were performed for the first time with use of extended X-ray absorption fine structure (EXAFS) and X-ray diffraction (XRD) techniques, supplemented by photoelectron measurements. XRD unanimously indicated a single phase NaCl-type structure of these compounds. Analysis of Mn K-edge EXAFS data provided us with the bond length and Debye–Waller (DW) factor for Mn–Te bond in octahedral coordination of rocksalt Sn 1− x Mn x Te. The magnitude of DW factor suggested a moderate ionicity of Mn–Te bond (in the host SnTe matrix) indicative of its mixed covalent–ionic character. The determined value of Mn–Te bond length in Sn 1− x Mn x Te enabled us to estimate the octahedral covalent radius of Mn.

X-ray characterization of precipitates in cerium-doped PbTe and SnTe crystals

The homogeneity, solid solubility, and chemical bonds in the new materials PbTe, SnTe doped with Ce were investigated. Scanning electron microscope observation and electron probe microanalysis carried out on PbTe crystals doped with Ce, revealed three types of Ce-rich precipitates with following compositions: CeTe2, Ce3Te7, Ce2Te5 and small admixture of PbTe in precipitates. The solubility of Ce in PbTe matrix was estimated as 0.5±0.1 at. %. The solubility of PbTe in CeTe2 and Ce3Te7 was found to be 3±0.5 at. %, but 7±0.5 at. % in the case of Ce2Te5. In SnTe crystal doped with Ce only one kind of precipitate with composition Ce2SnTe5 was found. Cerium solubility in SnTe matrix was estimated to be 1±0.25 at. %. According to our knowledge this is the first report of the identification of Ce2SnTe5 compound. The similar compounds Ce2SnS5 and Ce2SnSe5 are known.

Valency of Selected Rare-Earth Ions in SnTe Matrix

X-ray photoelectron spectroscopy experiments on SnTe crystals doped by Sm, Eu, and Yb were performed to determine the valency of these ions in the SnTe matrix. The analysis of the X-ray photoelectron spectroscopy valence-band spectra revealed that Eu and Yb are divalent while Sm is trivalent in SnTe. These conclusions were confirmed by studies of the binding energies of core levels (4d-levels of Yb and 3d-levels of Sm and Eu), which are not presented here.

Various Types of Magnetism in SnTe Crystals Doped with 3d Transition Metals

Magnetization measurements have been carried out to study various types of magnetism in degenerate magnetic semiconductors Sn 1- x (Me) x Te with different 3d transition metals Me=Cr, Fe, Co, and Ni. Of these impurities with x =1 at.%, only Cr and Fe act as ferromagnetic centers, while Co and Ni are magnetically ineffective in the host SnTe matrix which has a strong diamagnetic background. In particular, Sn 1- x Cr x Te (0.2 at.%< x <2 at.%) exhibits a ferromagnetic transition at the Curie temperature T c which varies from 150 K to 300 K depending on the Cr concentration and the annealing. This transition was confirmed by the anomalies in the spin resonance (g-value and linewidth), the resistivity, and the specific heat.