Spark Plasma Sintered Bulk Nanocomposites of Bi2Te2.7Se0.3 Nanoplates Incorporated Ni Nanoparticles with Enhanced Thermoelectric Performance

Optimization mechanism of laminated ceramic package structure on the regulation of semiconductor cooling performance

The refrigeration performance of semiconductor refrigeration devices is limited by, among other things, the thermal conductivity of the materials. Optimisation of ceramic materials for semiconductor packaging offers the possibility of improving system performance. In this paper, a mathematical model of the semiconductor refrigeration process is established using the cooling capacity and the cooling coefficient as evaluation indexes. It investigates the effects of current, cold end temperature and hot end temperature on the cooling performance. A simulation model of laminated encapsulated materials is proposed to investigate the influence of the structure of encapsulated ceramic materials on the condensation effect. The results show that a small increase in current significantly increases the cooling capacity at low cold-end temperatures, while this effect diminishes at higher cold-end temperatures. An increase in the hot end temperature decreases the cooling capacity and coefficient, with the decrease being more pronounced at higher currents. In addition, as the thermal conductivity of the encapsulated ceramic material decreases along the direction perpendicular to the ceramic structure, heat transfer is directed more effectively, resulting in improved cooling efficiency and condensation. These findings provide new insights into the design of ceramic materials and optimisation of the efficiency of semiconductor cooling systems.

Heterogeneous Cu Doping Facilitates Excellent Thermoelectric and Mechanical Performance in n-Type SnSe Composites

SnSe materials have attracted extensive attention in thermoelectrics due to their low thermal conductivity. Nevertheless, the thermoelectric properties of n-type polycrystalline SnSe are still low, and metallic Sn distributed in the SnSe1-x materials would affect the repeatability of thermoelectric performance. Herein, the thermoelectric properties of n-type polycrystalline SnSe0.95-based composites are highly enhanced by heterogeneous Cu doping. The carrier concentration of the SnSe0.95 material was optimized by SnCl2 doping. The strategy of heterogeneous Cu doping is employed in further improving the thermoelectric performance of the SnCl2-doped SnSe0.95 materials. In addition, partial Cu+ doping tunes the electron concentration to enhance the Seebeck coefficient. Moreover, metallic Sn distributed along the grain boundaries can be stabilized by forming Cu6Sn5 alloys, which improve the thermal stability of bulk composites. Excessive Cu particles and SnCl2 precipitates strengthen phonon scattering for lowering the lattice thermal conductivity. Ultimately, a peak ZT of 1.55 is yielded at 773 K in the SnSe0.95-1 wt % SnCl2-1 wt % Cu bulk composite, whose mechanical hardness is also increased. Hence, these results promote a feasible approach to simultaneously enhance the thermoelectric and mechanical properties of n-type SnSe-based composites, which might be worth exploring in other thermoelectric materials.

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.

Boosting Thermoelectric Performance in Nanocrystalline Ternary Skutterudite Thin Films through Metallic CoTe2 Integration

Metal-semiconductor nanocomposites have emerged as a viable strategy for concurrently tailoring both thermal and electronic transport properties of established thermoelectric materials, ultimately achieving synergistic performance. In this investigation, a series of nanocomposite thin films were synthesized, embedding metallic cobalt telluride (CoTe2) nanophase within the nanocrystalline ternary skutterudite (Co(Ge1.22Sb0.22)Te1.58 or CGST) matrix. Our approach harnessed composition fluctuation-induced phase separation and in situ growth during thermal annealing to seamlessly integrate the metallic phase. The distinctive band structures of both materials have developed an ohmic-type contact characteristic at the interface, which raised carrier density considerably yet negligibly affected the mobility counterpart, leading to a substantial improvement in electrical conductivity. The intricate balance in transport properties is further influenced by the metallic CoTe2 phase's role in diminishing lattice thermal conductivity. The presence of the metallic phase instigates enhanced phonon scattering at the interface boundaries. Consequently, a 2-fold enhancement in the thermoelectric figure of merit (zT ∼ 1.30) is attained with CGST-7 wt. % CoTe2 nanocomposite film at 655 K compared to that of pristine CGST.

Optimization of the Consolidation Parameters for Enhanced Thermoelectric Properties of Gr-Bi2Te2.55Se0.45 Nanocomposites

Hot pressing represents a promising consolidation technique for ball-milled bismuth telluride alloys, yet deep investigations are needed to understand its effect on the thermoelectric properties. This paper studies the effect of hot-pressing parameters (temperature and pressure) on the thermoelectric properties of the n-type Gr-Bi2Te2.55Se0.45 nanocomposite. Ultra-high pressure, up to 1.5 GPa, is considered for the first time for consolidating Bi2(Te,Se)3 alloys. Results from this study show that increasing the temperature leads to changes in chemical composition and causes noticeable grain growth. On the contrary, increasing pressure mainly causes improvements in densification. Overall, increments in these two parameters improve the ZT values, with the temperature parameter having a higher influence. The highest ZT of 0.69 at 160 °C was obtained for the sample hot-pressed at 350 °C and 1 GPa for 5 min, which is indeed an excellent and competitive value when compared with results reported for this n-type Bi2Te2.55Se0.45 composition.

Improved Thermoelectric Performance of Sb2Te3 Nanosheets by Coating Pt Particles in Wide Medium-Temperature Zone

The p-type Sb2Te3 alloy, a binary compound belonging to the V2VI3-based materials, has been widely used as a commercial material in the room-temperature zone. However, its low thermoelectric performance hinders its application in the low-medium temperature range. In this study, we prepared Sb2Te3 nanosheets coated with nanometer-sized Pt particles using a combination of solvothermal and photo-reduction methods. Our findings demonstrate that despite the adverse effects on certain properties, the addition of Pt particles to Sb2Te3 significantly improves the thermoelectric properties, primarily due to the enhanced electronic conductivity. The optimal ZT value reached 1.67 at 573 K for Sb2Te3 coated with 0.2 wt% Pt particles, and it remained above 1.0 within the temperature range of 333-573 K. These values represent a 47% and 49% increase, respectively, compared to the pure Sb2Te3 matrix. This enhancement in thermoelectric performance can be attributed to the presence of Pt metal particles, which effectively enhance carrier and phonon transport properties. Additionally, we conducted a Density Functional Theory (DFT) study to gain further insights into the underlying mechanisms. The results revealed that Sb2Te3 doped with Pt exhibited a doping level in the band structure, and a sharp rise in the Density of States (DOS) was observed. This sharp rise can be attributed to the presence of Pt atoms, which lead to enhanced electronic conductivity. In conclusion, our findings demonstrate that the incorporation of nanometer-sized Pt particles effectively improves the carrier and phonon transport properties of the Sb2Te3 alloy. This makes it a promising candidate for medium-temperature thermoelectric applications, as evidenced by the significant enhancement in thermoelectric performance achieved in this study.

High Thermoelectric Performance in Cu-Doped Bi2Te2.7Se0.33 Due to Cl Doping and Multiscale AgBiSe2

The thermoelectric performance of n-type Bi2Te3 needs further enhancement to match that of its p-type Bi2Te3 counterpart and should be considered for competitive applications. Combining Cu/Cl and multiscale additives (AgBiSe2) presents a suitable route for such enhancement. This is evidence of the enhanced thermoelectric performance of Bi1.995Cu0.005Te2.69Se0.33Cl0.03. Moreover, by incorporating 0.65 wt % AgBiSe2 (ABS) into Bi1.995Cu0.005Te2.69Se0.33Cl0.03, we further reduce its lattice thermal conductivity to ∼0.28 W m-1 K-1 at 353 K owing to the extra phonon scattering of multiscale ABS. Additionally, the Seebeck coefficient enhances (-183.89 μV K-1 at 353 K) owing to the matrix's reduced carrier concentration caused by ABS. As a result, we achieve a high ZT of ∼1.25 (at 353 K) and a high ZTave of ∼1.12 at 300-433 K for Bi1.995Cu0.005Te2.69Se0.33Cl0.03 + 0.65 wt % ABS. This work provides a promising strategy for enhancing the thermoelectric performance of n-type Bi2Te3 through Cu/Cl doping and ABS incorporation.

Energy-Saving Pathways for Thermoelectric Nanomaterial Synthesis: Hydrothermal/Solvothermal, Microwave-Assisted, Solution-Based, and Powder Processing

The pillars of Green Chemistry necessitate the development of new chemical methodologies and processes that can benefit chemical synthesis in terms of energy efficiency, conservation of resources, product selectivity, operational simplicity and, crucially, health, safety, and environmental impact. Implementation of green principles whenever possible can spur the growth of benign scientific technologies by considering environmental, economical, and societal sustainability in parallel. These principles seem especially important in the context of the manufacture of materials for sustainable energy and environmental applications. In this review, the production of energy conversion materials is taken as an exemplar, by examining the recent growth in the energy-efficient synthesis of thermoelectric nanomaterials for use in devices for thermal energy harvesting. Specifically, "soft chemistry" techniques such as solution-based, solvothermal, microwave-assisted, and mechanochemical (ball-milling) methods as viable and sustainable alternatives to processes performed at high temperature and/or pressure are focused. How some of these new approaches are also considered to thermoelectric materials fabrication can influence the properties and performance of the nanomaterials so-produced and the prospects of developing such techniques further.

Enhanced Thermoelectric Performance of GeTe-Based Composites Incorporated with Fe Nanoparticles

Incorporated nanoscale phases in thermoelectric (TE) materials can optimize the electronic and thermal transport properties to obtain high-performance TE materials. The rapid spark plasma sintering (SPS) technique is adopted to synthesize Ge_0.96Bi_0.06Te composites incorporated with soft magnetic Fe nanoparticles (nano-Fe) and their thermoelectric performance is researched in this study. With the phase transition of the Ge_0.96Bi_0.06Te matrix from the low-temperature rhombohedral phase to the high-temperature cubic one, the interface contact between Ge_0.96Bi_0.06Te and nano-Fe is transformed from Schottky contact to Ohmic one, which improves its electronic transport performance at high temperatures. At the same time, the additional Fe nanoprecipitation phonon scattering can reduce the lattice thermal conductivity to ∼0.66 W m^-1 K^-1. These mechanisms result in a high ZT value of 1.65 and a relatively highquality factor B of 1.05 at 785 K for Ge_0.96Bi_0.06Te/2 mol % Fe. This work suggests that the thermoelectric performance of composite materials can be enhanced by introducing a variable interface band structure.

Enhancing thermoelectric performance of n-type Bi2Te2.7Se0.3 through incorporation of Ag9AlSe6 inclusions

Bi2Te2.7Se0.3 (BTS) is the best commercial n-type thermoelectric alloy near room temperatures. However, as compared to its p-type counterpart its figure of merit (ZT) and the energy conversion efficiency is...

Isotropic Thermoelectric Performance of Layer-Structured n-Type Bi2Te2.7Se0.3 by Cu Doping

The lamellar structure of (Bi,Sb)₂(Te,Se)₃ alloys makes it difficult to achieve isotropic thermoelectric properties in the directions along and perpendicular to the c-axis, especially for n-type samples. In this work, by introducing Cu in polycrystalline n-type Cu_xBi₂Te_2.7Se_0.3 and applying the traditional synthesis process of high-energy ball milling and hot pressing, substantial enhancement of the thermoelectric figure of merit zT is obtained in both in-plane and out-of-plane directions. The intercalated Cu not only provides electron transport media for mobility improvement but also reduces the lattice thermal conductivity owing to the strain fluctuation. Typically, the van der Waals gap in the out-of-plane direction leads to relatively slower mobility and lower lattice thermal conductivity. Taking into account the same average density-of-state effective mass (m_avg^* ∼ 1.5m_e) predicted based on a single parabolic model, the obtained quality factor β is comparable in both directions. As a result, a peak zT ∼ 1.05 at 420 K and the average zT approaching to 1.0 in the temperature range 300-500 K are obtained in both directions for the Cu_0. 02Bi₂Te_2.7Se_0.3 sample. The simple synthesis process and isotropic thermoelectric properties in this work make n-type Bi₂Te₃ more convenient for potential production and application.

Practical High-Performance (Bi,Sb)2Te3-Based Thermoelectric Nanocomposites Fabricated by Nanoparticle Mixing and Scrap Recycling

Bi₂Te₃-based compounds are the most mature and widely used thermoelectric materials. However, industrial device fabrication will inevitably produce a lot of Bi₂Te₃ scraps, which results in wastes of expensive material resources. In this work, we recycled p-type (Bi,Sb)₂Te₃ scraps and reprocessed them by making nanocomposites with nano-SiC. The thermoelectric performance was enhanced, and a high ZT value of 1.07 was achieved, which is a significant improvement compared with commercial p-type (Bi,Sb)₂Te₃ ingots. Also, the hardness showed a notable increase, which is beneficial for device fabrication. In addition, we adjusted the proportion of Bi/Te of the commercial p-type (Bi,Sb)₂Te₃ scraps, thereby improving the thermoelectric performance and obtaining a higher ZT value of 1.2.

Achieving a High Average zT Value in Sb2Te3-Based Segmented Thermoelectric Materials

A tiny amount of Mn is doped in In_0.15Sb_1.85Te₃ sample to tailor its carrier concentration, thus boosting the power factor and suppressing the bipolar effect. Furthermore, large amounts of nanotwins are constructed to effectively scatter the phonons and reduce the lattice thermal conductivity. As a result, the zT value of Mn_0.02In_0.15Sb_1.83Te₃ is enhanced up to 1.0 at 673 K, making this material a robust candidate for medium-temperature (500-673 K) thermoelectric applications. Then combining with the low-temperature thermoelectric material Mn_0.0075Bi_0.5Sb_1.4925Te₃ previously reported by our group and using nickel as a barrier layer, a high average zT value of 1.08 during a broad temperature range from 303 to 673 K together with an Ohmic contact interface bonding is achieved in the p-type segmented leg fabricated via simple one-step sintering. Finally, the maximum theoretical conversion efficiency with a temperature difference of 370 K reaches ∼12.7%.