https://onlinelibrary.wiley.com/doi/epdf/10.1002/admt.201700256

Thermoelectric Devices: A Review of Devices, Architectures, and Contact Optimization

https://iopscience.iop.org/article/10.7567/JJAP.56.05DA04/pdf

Thermoelectric silicides: A review

As a promising thermoelectric material, higher manganese silicides are composed of earth-abundant and eco-friendly elements, and have attracted extensive attention for future commercialization. In this review, the authors first summarize the crystal structure, band structure, synthesis method, and pristine thermoelectric performance of different higher manganese silicides. After that, the strategies for enhancing electrical performance and reducing lattice thermal conductivity of higher manganese silicides as well as their synergism are highlighted. The application potentials including the chemical and mechanical stability of higher manganese silicides and their energy conversion efficiency of the assembled thermoelectric modules are also summarized. By analyzing the current advances in higher manganese silicides, this review proposes that potential methods of further enhancing zT of higher manganese silicides, lie in enhancing electrical performance while simultaneously reducing lattice thermal conductivity via reducing effective mass, optimizing carrier concentration, and nanostructure engineering.

https://espace.library.uq.edu.au/view/UQ:727627/UQ727627_OA.pdf

Eco-Friendly Higher Manganese Silicide Thermoelectric Materials: Progress and Future Challenges

Within the last decade, novel materials concepts and nanotechnology have resulted in a great increase of the conversion efficiency of thermoelectric materials. Despite this, a mass market for thermoelectric heat-to-electricity conversion is yet to be opened up. One reason for this is that the transfer of the lab records into fabrication techniques which enable thermoelectric generator modules is very challenging. By closing the gap between record lab values and modules, broad industrial applications may become feasible. In this review, we compare three classes of materials, all designed for medium-high to high temperature applications in the field of waste heat recovery: skutterudites, half-Heusler compounds, and silicon-based materials. Common to all three classes of thermoelectric materials is that they are built from elements which are neither scarce (e.g. tellurium) nor toxic (e.g. lead) and therefore may be the foundation of a sustainable technology. Further, these materials can provide both, n-type and p-type materials with similar performance and thermomechanical properties, such that the fabrication of thermoelectric generator modules has already been successfully demonstrated. The fabrication processes of the presented materials are scalable or have already been scaled up. The availability of thermoelectric materials is only one important aspect for the development of thermoelectric generator modules and heat conversion systems based on this technology. The design and configuration of the thermoelectric generator modules is similarly important. Hence, basic considerations of module configuration and different fundamental layouts of the thermoelectric heat-to-electricity conversion system are discussed within an additional chapter of this review.

/pdf/concepts-for-medium-high-to-high-temperature-thermoelectric-28t5rglw46.pdf

Concepts for medium-high to high temperature thermoelectric heat-to-electricity conversion: a review of selected materials and basic considerations of module design

Silicon is the most important element of modern semiconductor industry. As a thermoelectric converter material, it would be able to promote applications dramatically since device integration and scaling of the fabrication processes could be borrowed from existing technology. Though the thermoelectric performance of single crystalline silicon is only poor, silicon nanostructures have demonstrated a competitive figure of merit. To make use of these nanostructures, novel device architectures are necessary. This review provides an overview over the physical background of silicon as thermoelectric converter material as well as different nanostructures like nanowires, porous nanomeshes, and nanocrystalline bulk and their thermoelectric properties, focusing mostly on experimental data. Further, different thermoelectric converter device concepts including nanowire device concepts, pn junction thermoelectric generators and integrated spot coolers are discussed and their realization with silicon nanostructures briefly sketched. 



(a) Nanowires, porous nanomeshes and nanocrystalline bulk with promising thermoelectric material's figure of merit. (b) Innovative device concepts using nanowires or large area pn junctions for thermoelectric heat-to-electricity conversion.

Silicon nanostructures for thermoelectric devices: A review of the current state of the art

Nanostructured silicon germanium thermoelectric materials prepared by mechanical alloying and sintering method have recently shown large enhancement in figure-of-merit, ZT. The fabrication of these structures often involves many parameters whose understanding and precise control is required to attain large ZT. In order to find the optimum parameters for further enhancing the ZT of this material, we have grown and studied both experimentally and theoretically different nanostructured p-type SiGe alloys. The effect of various parameters of milling process and sintering conditions on the thermoelectric properties of the grown samples were studied. The electrical and thermal properties were calculated using Boltzmann transport equation and were compared with the data of nanostructured and crystalline SiGe. It was found that the thermal conductivity not only depends on the average crystallite size in the bulk material, but also it is a strong function of alloying, porosity, and doping concentration. The Seebeck coefficient showed weak dependency on average crystallite size. The electrical conductivity changed strongly with synthesis parameters. Therefore, depending on the synthesis parameters the figure-of-merit reduced or increased by ∼60% compared with that of the crystalline SiGe. The model calculation showed that the lattice part of thermal conductivity in the nanostructured sample makes ∼80% of the total thermal conductivity. In addition, the model calculation showed that while the room temperature hole mean free path (MFP) in the nanostructured sample is dominated by the crystallite boundary scattering, at high temperature the MFP is dominated by acoustic phonon scattering. Therefore, the thermal conductivity can be further reduced by smaller crystallite size without significantly affecting the electrical conductivity in order to further enhance ZT.

The effect of synthesis parameters on transport properties of nanostructured bulk thermoelectric p-type silicon germanium alloy

Synthesis, characterization, and thermoelectric properties of nanostructured bulk p-type MnSi1.73, MnSi1.75, and MnSi1.77

Higher manganese silicide (HMS) is a useful thermoelectric material for waste heat recovery in medium to high temperature range. It is made from two of the most abundant materials on earth. Moreover, it is non-toxic and environmentally responsible. A low-cost, scalable, and quick method of synthesizing bulk thermoelectric higher manganese silicide is proposed for its industrial manufacturing. Heat treatment alloying of higher manganese silicide powder is proposed for producing its large quantity in a cost effective way. The process involves heat treatment of the elemental powders at 1050 °C for 1 hour. Thermoelectric properties of the resultant samples were studied and compared with the samples made by mechanical alloying. In comparison, both methods result in similar trends in thermoelectric properties however with significant cost reduction and ease of fabrication for the proposed method.

Cost Effective Synthesis of Bulk Thermoelectric Higher Manganese Silicide for Waste Heat Recovery and Environmental Protection

Higher manganese silicide is one of the promising thermoelectric materials for waste heat recovery at medium temperature (500-700 °C). Improvement on thermoelectric performance of bulk thermoelectric higher manganese silicide MnSi1.75 is introduced by externally mixing 1 at% nanostructured MnSi to MnSi1.75. This method can reduce the thermal conductivity above 400 °C more than reducing the power factor of the higher manganese silicide. This would enhance the figure-of-merit ZT of MnSi1.75 to ZT0.5 without any doping at 570 °C. In comparison, the figure-of-merit of conventional MnSi1.75 is ZT0.3. This method can be easily applied to industrial manufacturing of this material to enhance its efficiency.

/pdf/enhancement-of-thermoelectric-efficiency-of-mnsi1-75-with-1tqtxnpsvm.pdf

Enhancement of Thermoelectric Efficiency of MnSi1.75 with the Addition of Externally Processed Nanostructured MnSi

Thermoelectric technology is becoming one of the important elements in sustainable energy due to its capability in green conversion of waste heat into electricity Solid solution alloys based on Bi2Te3 have been some of the most efficient thermoelectric materials near the room temperature for many years Recently there have been advances in the thermoelectric efficiency of (BixSb1-x)2Te3 alloy via bulk nanostructuring The fabrication process of the alloy from elements of Bi, Sb, and Te often involves mechanical alloying with extensive milling time This process is slow and consumes significant electric power Here we report and compare three different methods to prepare powders of Bi2Te3 and Sb2Te3 binary alloys and (BixSb1-x)2Te3 ternary alloys: conventional high energy mechanical milling and two alternative methods namely induction melting and thermomechanical method In all three methods the obtained powders are single phase and possess good homogeneity Efficiency and advantages of different methods have been discussed Alternative techniques introduced in this work provide a more efficient approach with higher yield for large scale preparation of (BixSb1-x)2Te3 thermoelectric structures

Xinghua Shi

Papers

The effect of synthesis parameters on transport properties of nanostructured bulk thermoelectric p-type silicon germanium alloy

Synthesis, characterization, and thermoelectric properties of nanostructured bulk p-type MnSi1.73, MnSi1.75, and MnSi1.77

Cost Effective Synthesis of Bulk Thermoelectric Higher Manganese Silicide for Waste Heat Recovery and Environmental Protection

Enhancement of Thermoelectric Efficiency of MnSi1.75 with the Addition of Externally Processed Nanostructured MnSi

Economical Preparation of Nanostructured Bulk (BixSb1-X)2Te3 Thermoelectrics