Sb Te Research Articles

Prefer‐Oriented Ag2Se Crystal for High‐Performance Thermoelectric Cooling

AbstractAg2Se‐based materials with promising room‐temperature thermoelectric performance have been known for decades. However, thermoelectric cooling devices based on bulk Ag2Se have seldom been reported, mainly due to the phase transition ≈400 K poses a grand challenge for leg design and module integration. Herein, Ag2Se crystals with the preferred orientation have been prepared. A high carrier mobility of ≈1846 cm2 V−1 s−1 and a power factor of ≈31.2 µW cm−1 K−2 at room temperature has been realized, and results in a zT of ≈0.95 at 300 K. Importantly, by applying Ag as the contact layer, the Ag/Ag2Se/Ag joint has been prepared by one‐step sintering. By maintaining the pressure of ≈10 MPa after sintering and during the reflow soldering, the deleterious effect of the large thermal expansion can be alleviated. The contact resistance of the Ag/Ag2Se interface is as low as ≈2.9 µΩ cm2, indicating negligible electrical parasitic loss. The thermoelectric device with 7 pairs of Ag2Se and (Bi, Sb)2Te3 has been fabricated and it can achieve a maximum cooling power of ≈2.90 W and a cooling temperature difference of ≈70.4 K at the hot‐side temperature of 350 K, demonstrating the great potential of Ag2Se for cooling applications.

Strong and efficient bismuth telluride-based thermoelectrics for Peltier microcoolers.

Thermoelectric Peltier coolers (PCs) are being increasingly used as temperature stabilizers for optoelectronic devices. Increasing integration drives PC miniaturization, requiring thermoelectric materials with good strength. We demonstrate a simultaneous gain of thermoelectric and mechanical performance in (Bi, Sb)2Te3, and successfully fabricate micro PCs (2×2mm2 cross-section) that show excellent maximum cooling temperature difference of 89.3K with a hot-side temperature of 348K. A multi-step process involving annealing, hot-forging and composition design, is developed to modify the atomic defects and nano- and microstructures. The peak ZT is improved to ∼1.50 at 348K, and the flexural and compressive strengths are significantly enhanced to ∼140MPa and ∼224MPa, respectively. These achievements hold great potential for advancing solid-state refrigeration technology in small spaces.

Ge Enrichment of Ge–Sb–Te Alloys as Keystone of Flexible Edge Electronics

Ge Enrichment of Ge–Sb–Te Alloys as Keystone of Flexible Edge Electronics

Exceptional thermoelectric and mechanical performance in (Bi, Sb)2Te3 matrix facilitated by AgInSe2 alloying

The emerging fields of the Internet of Things, intelligent robotics, and smart biomedical devices have sparked an increasing demand for high-performance thermoelectric (TE) devices due to their efficient conversion of thermal energy into electrical power, and vice versa. The environmentally friendly (Bi, Sb)2Te3 (BST) system, which displays superior performance near room temperature, offers a promising solution for optimizing thermoelectrics to meet the needs of commercial applications. Here, we utilized AgInSe2 alloying to enhance the TE and mechanical properties of BST, aiming to optimize electron and phonon transport and elucidate the underlying mechanisms. The synergistic optimization resulted in a peak zT of ∼ 1.3 at 353 K and an average zTave of ∼ 1.11 from 303 K to 503 K in BST-0.1 %AgInSe2, as well as a high Vickers hardness of ∼ 105 Hv. Through rational optimization of the TE device, we achieved a maximum conversion efficiency of ∼ 6 % at a temperature difference of 210 K. Leveraging the robust TE output of the device, we further evaluated its potential as a self-powered information interaction wristband device based on ASCII codes. We envisage this versatile TE device being extensively applied in power generation and human–machine interaction, with promising potential in wearable electronics, telecommunications, and healthcare monitoring.

Grain Manipulation by Annealing Treatment Realizes High-Performance N-Type Bi2Te2.4Se0.6 Thermoelectric Material and Device.

Bi2Te3-based materials play a crucial role in solid cooling and power generation, but the rapidly deteriorated ZT with rising temperatures above 450 K severely limits further applications. Here, this paper reports a novel preparation method of annealing treatment for molten ingot, which can enhance the thermoelectric performance of n-type Bi2Te2.4Se0.6 in a wide temperature range. Instead of conventional halides, copper is adopted to regulate the carrier concentration and grain size to optimal levels. During the process of annealing at 573 K for 4h, the number of twins significantly increases and the grains of Cu-doped samples become larger and more oriented. These optimizations lead to higher carrier mobility with similar carrier concentration compared with the sample without heat treatment. The synergistic effects of Cu doping and annealing treatment realize a high average ZT of 0.89 within 300-600 K in n-type Cu0.02Bi2Te2.4Se0.6. Combined with p-type (Bi,Sb)2Te3, the fabricated thermoelectric device exhibits a high conversion efficiency of 6.9% at a temperature difference of 300 K. This study suggests that annealing treatment is a simple and effective scheme to promote the applications of n-type Bi2(Te,Se)3 in a wide temperature range.

Solution-derived Ge–Sb–Se–Te phase-change chalcogenide films

Ge–Sb–Se–Te chalcogenides, namely Se-substituted Ge–Sb–Te, have been developed as an alternative optical phase change material (PCM) with a high figure-of-merit. A need for the integration of such new PCMs onto a variety of photonic platforms has necessitated the development of fabrication processes compatible with diverse material compositions as well as substrates of varying material types, shapes, and sizes. This study explores the application of chemical solution deposition as a method capable of creating conformally coated layers and delves into the resulting modifications in the structural and optical properties of Ge–Sb–Se–Te PCMs. Specifically, we detail the solution-based deposition of Ge–Sb–Se–Te layers and present a comparative analysis with those deposited via thermal evaporation. We also discuss our ongoing endeavor to improve available choice of processing-material combinations and how to realize solution-derived high figure-of-merit optical PCM layers, which will enable a new era for the development of reconfigurable photonic devices.

Room temperature-produced chalcogenide superlattices for interfacial phase-change memory

Phase-change memory (PCM) using chalcogenide films composed of Ge–Sb–Te alloys is the only commercially available nonvolatile memory for storage class memory. Recently, superlattice films of GeTe and Sb2Te3, called interfacial PCM (iPCM), have attracted attention for further increasing the switching speed and reducing energy consumption. It has been reported that the iPCM device exhibits both unipolar- and bipolar-type resistive switching depending on the method of voltage application, and research is being conducted to advance its applications. However, all iPCMs reported thus far have been formed at high temperatures beyond the crystallization temperatures of GeTe and Sb2Te3 using vacuum chambers equipped with a heating stage, making mass production and practical application difficult. Here, we report on fabricated superlattice composed of S-doped GeTe and Sb2Te3 layers by combining room temperature deposition with subsequent two-step annealing. Upon evaluating the performance of this superlattice film as a bipolar-type iPCM, it was found to exhibit characteristics comparable to those of bipolar-type iPCM fabricated from high-temperature deposited superlattices. This technology is expected to contribute to an increase in the throughput of iPCM device manufacturing.

Stable chalcogenide Ge–Sb–Te heterostructures with minimal Ge segregation

Matching of various chalcogenide films shows the advantage of delivering multilayer heterostructures whose physical properties can be tuned with respect to the ones of the constituent single films. In this work, (Ge–Sb–Te)-based heterostructures were deposited by radio frequency sputtering on Si(100) substrates and annealed up to 400 °C. The as-deposited and annealed samples were studied by means of X-ray fluorescence, X-ray diffraction, scanning transmission electron microscopy, electron energy loss spectroscopy and Raman spectroscopy. The heterostructures, combining thermally stable thin layers (i. e. Ge-rich Ge5.5Sb2Te5, Ge) and films exhibiting fast switching dynamics (i. e. Sb2Te3), show, on the one side, higher crystallization-onset temperatures than the standard Ge2Sb2Te5 alloy and, on the other side, none to minimal Ge-segregation.

Synergistic Tailoring of Electronic and Thermal Transports in Thermoelectric Se-Free n-Type (Bi,Sb)2Te3.

Se-free n-type (Bi,Sb)2Te3 thermoelectric materials, outperforming traditional n-type Bi2(Te,Se)3, emerge as a compelling candidate for practical applications of recovering low-grade waste heat. A 100% improvement in the maximum ZT of n-type Bi1.7Sb0.3Te3 is demonstrated by using melt-spinning and excess Te-assisted transient liquid phase sintering (LPS). Te-rich sintering promotes the formation of intrinsic defects (TeBi), elevating the carrier concentration and enhancing the electrical conductivity. Melt-spinning with excess Te fine-tunes the electronic band, resulting in a high power-factor of 0.35 × 10-3 W·m-1 K-2 at 300 K. Rapid volume change during sintering induces the formation of dislocation networks, significantly suppressing the lattice thermal conductivity (0.4 W·m-1 K-1). The developed n-type legs achieve a high maximum ZT of 1.0 at 450 K resulting in a 70% improvement in the output power of the thermoelectric device (7.7 W at a temperature difference of 250 K). This work highlights the synergy between melt-spinning and transient LPS, advancing the tailored control of both electronic and thermal properties in thermoelectric technology.

Direct Melt-Calendaring of Highly Textured (Bi,Sb)2Te3 Thick Films: Superior Thermoelectric and Mechanical Performance via Strain Engineering.

The evolutions of chip thermal management and micro energy harvesting put forward urgent need for micro thermoelectric devices. Nevertheless, low-performance thermoelectric thick films as well as the complicated precision cutting process for hundred-micron thermoelectric legs still remain the bottleneck hindering the advancement of micro thermoelectric devices. In this work, an innovative direct melt-calendaring manufacturing technology is first proposed with specially designed and assembled equipment, that enables direct, rapid, and cost-effective continuous manufacturing of Bi2Te3-based films with thickness of hundred microns. Based on the strain engineering with external glass coating confinement and controlled calendaring deformation degree, enhanced thermoelectric performance has been achieved for (Bi,Sb)2Te3 thick films with highly textured nanocrystals, which can promote carrier mobility over 182.6 cm2 V-1 s-1 and bring out a record-high zT value of 0.96 and 1.16 for n-type and p-type (Bi,Sb)2Te3 thick films, respectively. The nanoscale interfaces also further improve the mechanical strength with excellent elastic modules (over 42.0GPa) and hardness (over 1.7GPa), even superior to the commercial zone-melting ingots and comparable to the hot-extrusion (Bi,Sb)2Te3 alloys. This new fabrication strategy is versatile to a wide range of inorganic thermoelectric thick films, which lays a solid foundation for the development of micro thermoelectric devices.

Localized Surface Doping Induced Ultralow Contact Resistance between Metal and (Bi,Sb)2Te3 Thermoelectric Films.

Micro thermoelectric devices are expected to further improve the cooling density for the temperature control of electronic devices; nevertheless, the high contact resistivity between metals and semiconductors critically limits their applications, especially in chip cooling with extremely high heat flux. Herein, based on the calculated results, a low specific contact resistivity of ∼10-7 Ω cm2 at the interface is required to guarantee a desirable cooling power density of micro devices. Thus, we developed a generally applicable interfacial modulation strategy via localized surface doping of thermoelectric films, and the feasibility of such a doping approach for both n/p-type (Bi,Sb)2Te3 films was demonstrated, which can effectively increase the surface-majority carrier concentration explained by the charge transfer mechanism. With a proper doping level, ultralow specific contact resistivities at the interfaces are obtained for n-type (6.71 × 10-8 Ω cm2) and p-type (3.70 × 10-7 Ω cm2) (Bi,Sb)2Te3 layers, respectively, which is mainly attributed to the carrier tunneling enhancement with a narrowed interfacial contact barrier width. This work provides an effective scheme to further reduce the internal resistance of micro thermoelectric coolers, which can also be extended as a kind of universal interfacial modification technique for micro semiconductor devices.

Investigation of thermal stability improvement in Nb doped Sb2Te3

The phase change material Sb2Te3 (ST) exhibits a fast-switching speed and poor thermal stability because the four-fold rings are dominant and homo-polar bonds are absent in the amorphous state. Many studies have been performed on the improvement of phase change properties. Chemical doping methods have been widely used because additional chemical bonds are formed between the doped element and host atoms, leading to the modification of the local structure and electronic band structure. Previous reports have indicated the importance of the bond length and lattice mismatch in element doped ST. In this study, the electronegativity of the doped elements was investigated because it determines the strength of the bond via charge transfer between two atoms. A strong correlation between the electronegativity of the doped element and the phase change properties of the doped ST was observed. An ideal electronegativity range, which corresponds to some elements doped ST with excellent thermal stability, was found in this investigation. Nb atoms were selected as the optimal dopant to stabilize the amorphous phase of ST because Nb was in the ideal range. Additional homo-polar bonds and Nb-Te bonds can stabilize the amorphous phase because additional energy is required for ring reconstruction during crystallization. Consequently, the thermal stability and resistance difference of the Nb doped ST were significantly improved. In addition, the phase change speed of ST was not affected by Nb doping. This study highlights a new approach for pursuing better properties of phase change materials by chemical doping methods.

Improved Thermoelectric Performance in Ga‐ and Te‐Co‐introduced Tetrahedrite Cu12Sb4S13

As an earth‐abundant, environment‐friendly, and cost‐effective material, tetrahedrite Cu12Sb4S13 has attracted much attention in thermoelectrics (TEs). However, the TE performance of the pristine Cu12Sb4S13 (CSS) is mediocre, thereby much improvement is required. In this work, both the electronic and phonon transports of the CSS are engineered using Ga2Te3 as a dopant. In the results, it is indicated that dual substitutions of Ga for Cu and Te for Sb not only cause the enhancement of power factor via electronic band structure tuning, but also leads to a drop in both the electronic and lattice thermal conductivities. As a result, the total thermal conductivity (κ) decreases to 0.98 W m−1 K−1 at 770 K, which is about 58% that of the pristine CSS, thus improving the TE performance with the highest dimensionless figure of merit value increasing to 0.95 for (Cu12Sb4S13)0.9(Ga2Te3)0.1 at 773 K, 1.9 times that of the pristine CSS (≈0.5 at 770 K).

Unraveling electronic origins for boosting thermoelectric performance of p-type (Bi,Sb)2Te3.

P-type Bi2-xSbxTe3 compounds are crucial for thermoelectric applications at room temperature, with Bi0.5Sb1.5Te3 demonstrating superior performance, attributed to its maximum density-of-states effective mass (m*). However, the underlying electronic origin remains obscure, impeding further performance optimization. Herein, we synthesized high-quality Bi2-xSbxTe3 (00 l) films and performed comprehensive angle-resolved photoemission spectroscopy (ARPES) measurements and band structure calculations to shed light on the electronic structures. ARPES results directly evidenced that the band convergence along the [Formula: see text]-[Formula: see text] direction contributes to the maximum m* of Bi0.5Sb1.5Te3. Moreover, strategic manipulation of intrinsic defects optimized the hole density of Bi0.5Sb1.5Te3, allowing the extra valence band along [Formula: see text]-[Formula: see text] to contribute to the electrical transport. The synergy of the above two aspects documented the electronic origins of the Bi0.5Sb1.5Te3's superior performance that resulted in an extraordinary power factor of ~5.5 milliwatts per meter per square kelvin. The study offers valuable guidance for further performance optimization of p-type Bi2-xSbxTe3.

High Thermoelectric Performance of Ge–Sb–Te Nanosheets: A Density Functional Study

High Thermoelectric Performance of Ge–Sb–Te Nanosheets: A Density Functional Study

Understanding the role of additional Cu intercalation in electronic and thermal properties of p-type Cu2.9Te2-incorporated Bi0.5Sb1.5Te3 thermoelectric alloys

While extensive research has explored Cu doping in n-type Bi2(Te,Se)3 for its beneficial effects on reproducibility and mobility, its impact on p-type (Bi,Sb)2Te3 remains incompletely understood. Recently, Saglik et al. demonstrated Cu2.9Te2 incorporation into Bi0.5Sb1.5Te3 as a novel approach for simultaneous Cu doping and intercalation, surpassing prior studies focused solely on Cu doping at Bi/Sb sites. The influence of additional Cu intercalation on both electronic band parameters (density-of-states effective mass, deformation potential, and weighted mobility) and phonon scattering by point defects has yet to be investigated. Here, we employ the Effective Mass model to comparatively assess the impact of Cu intercalation on these band parameters relative to single Cu doping. Furthermore, the Callaway-von Baeyer and Debye-Callaway models are employed to evaluate the effect of Cu intercalation in scattering phonons. Our findings reveal that additional Cu intercalation effectively suppresses the lattice thermal conductivity of Bi0.5Sb1.5Te3 to the amorphous limit, offering the potential to improve the figure-of-merit (zT) to ∼2.0 near 420 K with optimized carrier concentration. This approach highlights Cu intercalation as a readily applicable and powerful tool for maximizing the thermoelectric performance of Bi2Te3-based materials.

EXPERIMENTAL STUDY OF THE PHASE EQUILIBRIA IN THE SnTe–Sb2Te3–Te SYSTEM

Phase equilibria of the SnTe–Sb2Te3–Te portion of the Sn–Sb–Te ternary system have been experimentally investigated using differential thermal analysis (DTA), powder X-ray diffraction (XRD), and microstructural analysis methods. Based on the measured experimental results and literature information, isothermal sections at 500 K, liquidus surface projection, and several vertical sections of the phase diagram were plotted. The 500 K phase diagram of this system consists of 2 single-phase regions, 2 two-phase regions, and 3 three-phase regions. The liquidus surface projection is represented by the primary crystallization fields of 5 phases. The primary crystallization fields of all phases, the types, and coordinates of non- and monovariant equilibria were determined. Obtained experimental data can be valuable input for design for Sn–Sb–Te-based alloys

Interfacial Reactions between Sn-Based Solders and n-Type Bi2(Te,Se)3 Thermoelectric Material.

This study investigated the interfacial reactions between n-type Bi2(Te,Se)3 thermoelectric material, characterized by a highly-oriented (110) plane, and pure Sn and Sn-3.0Ag-0.5Cu (wt.%) solders, respectively. At 250 °C, the liquid-state Sn/Bi2(Te,Se)3 reactions resulted in the formation of both SnTe and BiTe phases, with Bi-rich particles dispersed within the SnTe phase. The growth of the SnTe phase exhibited diffusion-controlled parabolic behavior over time. In contrast, the growth rate was considerably slower compared to that observed with p-type (Bi,Sb)2Te3. Solid-state Sn/Bi2(Te,Se)3 reactions conducted between 160 °C and 200 °C exhibited similar interfacial microstructures. The SnTe phase remained the primary reaction product, embedded with tiny Bi-rich particles, revealing a diffusion-controlled growth. However, the BiTe layer had no significant growth. Further investigation into growth kinetics of intermetallic compounds and microstructural evolution was conducted to elucidate the reaction mechanism. The slower growth rates in Bi2(Te,Se)3, compared to the reactions with (Bi,Sb)2Te3, could be attributed to the strong suppression effect of Se on SnTe growth. Additionally, the interfacial reactions of Bi2(Te,Se)3 with Sn-3.0Ag-0.5Cu were also examined, showing similar growth behavior to those observed with Sn solder. Notably, compared with Ag, Cu tends to diffuse towards the interfacial reaction phases, resulting in a high Cu solubility within the SnTe phase.

Mineralogical zoning of the PGE–Cu–Ni orebodies in the central part of the Oktyabr'sky Deposit, Norilsk District, Russia

AbstractMineralogical features of two orebodies, lenses (C-3 and C-4), at the central part of the Oktyabr'sky deposit have been investigated. Multidirectional mineralogical zoning in the northern and southern orebodies is shown, confirming the hypothesis of their formation from various magmatic flows, which have individual features and their own modes of formation. The southern C-3 and northern C-4 orebodies differ in their mineralogical associations: C-3 is characterised by a high-sulfur association of sulfides; and C-4 contains minerals with a sulfur deficit (talnakhite, sugakiite). Variations in Fe and Ni ratios in pentlandite are controlled by the volatility of sulfur during ore crystallisation. Direct crystallisation zoning is observed in the disseminated ores of the C-4 orebody (borehole RT-107), where the fugacity of sulfur ($f_{S_2}$) increases from bottom to top. In contrast in orebody C-3 (borehole RT-30) $f_{S_2}$ decreases in the same direction. This reverse zoning coincides with the vectors of the evolution of ore systems in various blocks of the Main Ore Body of the Oktyabr'sky deposit. The difference in typomorphic features of disseminated ores of the southern and northern orebodies is confirmed by differences in the associations of platinum-group element minerals (PGMs). Disseminated ores in picritic gabbro-dolerites and massive pyrrhotite ores in the exocontact of the intrusion within the southern orebody differ in the specialisation of PGMs: the former is characterised by minerals of the Pd–Bi–Sb–Te system, the latter by only Pt minerals. The similarity of these types of ores lies in the similar reverse mineralogical and geochemical zoning from top to bottom along the sections, caused by the evolution of the sulfide melt in this direction. The formation of reverse zoning of disseminated ores (zones of ‘marginal reversion’) is probably due to the action of a mechanism of repeated influx of a melt of an increasingly primitive composition into the upper parts of the crystallising flow. Unidirectional trends in massive and disseminated ores are more likely to be due to the action of the same type of mechanism.

GeSe ovonic threshold switch: the impact of functional layer thickness and device size

Three-dimensional phase change memory (3D PCM), possessing fast-speed, high-density and nonvolatility, has been successfully commercialized as storage class memory. A complete PCM device is composed of a memory cell and an associated ovonic threshold switch (OTS) device, which effectively resolves the leakage current issue in the crossbar array. The OTS materials are chalcogenide glasses consisting of chalcogens such as Te, Se and S as central elements, represented by GeTe6, GeSe and GeS. Among them, GeSe-based OTS materials are widely utilized in commercial 3D PCM, their scalability, however, has not been thoroughly investigated. Here, we explore the miniaturization of GeSe OTS selector, including functional layer thickness scalability and device size scalability. The threshold switching voltage of the GeSe OTS device almost lineally decreases with the thinning of the thickness, whereas it hardly changes with the device size. This indicates that the threshold switching behavior is triggered by the electric field, and the threshold switching field of the GeSe OTS selector is approximately 105 V/μm, regardless of the change in film thickness or device size. Systematically analyzing the threshold switching field of Ge–S and Ge–Te OTSs, we find that the threshold switching field of the OTS device is larger than 75 V/μm, significantly higher than PCM devices (8.1–56 V/μm), such as traditional Ge2Sb2Te5, Ag–In–Sb–Te, etc. Moreover, the required electric field is highly correlated with the optical bandgap. Our findings not only serve to optimize GeSe-based OTS device, but also may pave the approach for exploring OTS materials in chalcogenide alloys.