Materials Characterization of Cobalt Antimonide Nanostructures as Thermoelectric Material

Abstract

Cobalt antimonide (CoSb₃) nanoparticles, a binary skutterudite structure, are synthesized by following solvothermal method using water as solvent. The solvothermally processed powders are annealed to remove the excess Sb to achieve single phase CoSb₃ nanoparticles, and are examined by X-ray diffraction (XRD) indicating the formation of cubic phase of CoSb₃. The structural analysis by selected area electron diffraction (SAED) and the elemental composition of 1:3 for Co and Sb using energy dispersive X-ray spectrophotometer (EDX) predicts formation of high purity crystalline CoSb₃ nanoparticles. Morphology of the annealed CoSb₃ powders observed using field emission scanning electron microscope (FESEM) and transmission electron microscopy (TEM) indicates particle size of 50-100?nm. The ultraviolet–visible (UV-Vis) absorption spectroscopy estimates an energy gap of 3?eV. The nanosized CoSb₃ skutterudites are potential intermediate-temperature thermoelectric materials with further application in developing efficient thermoelectric modules.     

Partially coherent phonon transport in two-dimensionally rough nanowires

Rough surface nanowires exhibit a severely reduced thermal conductivity compared to the bulk. Their thermal conductivities are much below the value predicted from the diffuse scattering model. Such low thermal conductivities are particularly promising for thermoelectric applications. We extend our previous work on understanding this phenomenon using a model of partially coherent phonon transport. Considering both azimuthal and longitudinal roughness, we show that it is the latter that dominates thermal conductivity reduction. Our work advanced fundamental phonon boundary scattering that is key in applications ranging from semiconductor devices to thermoelectric materials.     

High temperature processing of ferroelectric thin films using interconnect wafer technology

Abstract

There is interest in ferroelectric thin films for uncooled IR detector applications. Currently the processing of these devices takes a fully integrated approach where the thin films are deposited directly onto underlying CMOS readout circuitry, thereby imposing severe limits on the thermal budget available for the crystallisation of the ferroelectric material. This is incommensurate with obtaining the best ferroelectric properties from materials such as lead scandium tantalate (PST) which requires elevated temperature processing to attain the highest merit figures for IR detection. In this paper thin film PST processed within the CMOS survivability envelope will be compared to that processed at temperatures up to 850°C. A novel interconnect wafer technology will be outlined which enables processing to be extended to such temperatures. It will be shown that elevated temperature processing of the PST film can result in dramatic improvement of the materials merit figure for IR detection     

微型温差电器件及相关材料的研究现状

1821年德国科学家塞贝克发现的塞贝克效应以及后来帕尔帖效应和汤姆逊效应开启了热电学的大门,人们应用这些效应先后制造出了各种温差电器件,如温差电发电器、温差电致冷器、温差电传感器、温差电探测器等。随着微电机系统(MEMS)技术、微电子技术引入温差电器件的制造,微型温差电器件吸引了越来越多的注意。介绍了近年美国、德国、中国等在微型温差电器件制造及材料研究方面的相关研究成果。     

Modeling and Management of Batteries and Ultracapacitors for Renewable Energy Support in Electric Power Systems–An Overview

Abstract—Energy storage devices and systems are playing a major role in all electrical systems from small electronics devices and automotive systems to the utility grid. The main objective of this article is to review energy storage devices, management, control, interface, and demonstrations for electrical power systems. Various types of energy storage systems are discussed, but the main focus is on batteries and ultracapacitors. Different types of batteries and their electrical models are explained. Three major types of ultracapcitors are also discussed. The battery management system and its functions, controls, and hardware are discussed. Various power electronics-based interface systems for battery and ultracapcitor charging and discharging are presented. Applications of energy storage systems for utility applications, including renewable firming, power shifting, and ancillary services, are discussed.     

Hot pressed pellets of thallium doped bismuth telluride alloys for thermoelectrics

ABSTRACT

Thallium doped bismuth telluride alloys (Bi_2-xTl_xTe₃) are synthesized using solvothermal method, and pellets are formed using hot-press machine by applying 60 MPa pressure at 553 K temperature for 5 min. The X-ray powder diffraction for the as-synthesized Bi_2-xTl_xTe₃ alloys indicates phase purity and crystallographic structures. Scanning electron microscopy indicates highly compact plate-like structures for hot-pressed pellets. The energy dispersive X-ray spectrophotometer predicts a stoichiometric ratio of 2:3 for Bi and Te in the Bi₂Te₃. The newly prepared Bi_2-xTl_xTe₃ pellets could be utilized as an efficient material in thermoelectric devices for power generation from waste heat.     

Modulation doping and energy filtering as effective ways to improve the thermoelectric power factor

Thermoelectric (TE) materials have undergone revolutionary progress over the last 20 years. The thermoelectric figure of merit ZT, which quantifies the ability of a material to convert heat into electricity has more than doubled compared to traditional values of \(ZT\sim 1\), reaching values even beyond \(ZT\sim 2\) in some instances. These improvements are mostly attributed to drastic reductions of the thermal conductivity in nanostructured materials and nanocomposites. However, as thermal conductivities in these structures approach the amorphous limit, any further benefits to ZT must be achieved through the improvement of the thermoelectric power factor. In this work we review two of the most promising avenues to increase the power factor, namely (i) modulation doping and (ii) electron energy filtering, and present a computational framework for analysis of these mechanisms for two example cases: low-dimensional gated Si nanowires (electrostatically achieved doping), and superlattices (energy filtering over potential barriers). In the first case, we show that a material with high charge density, but free of ionized impurities, can provide up to a five-fold thermoelectric power factors increase compared to the power factor of the doped material, which highlights the benefits of modulation doping, or gating of materials. In the second case, we show that optimized construction of energy barriers within a superlattice material geometry can improve the power factor by up to \(\sim 30\,\%\). This paper is intended to be a review of our main findings with regards to efforts to improve the thermoelectric power factor through modulation doping and energy filtering.     

Study of thermal properties of graphene-based structures using the force constant method

The thermal properties of graphene-based materials are theoretically investigated. The fourth-nearest neighbor force constant method for phonon properties is used in conjunction with both the Landauer ballistic and the non-equilibrium Green’s function techniques for transport. Ballistic phonon transport is investigated for different structures including graphene, graphene antidot lattices, and graphene nanoribbons. We demonstrate that this particular methodology is suitable for robust and efficient investigation of phonon transport in graphene-based devices. This methodology is especially useful for investigations of thermoelectric and heat transport applications.     

Applications of superconductivity to electric power equipment

A brief survey is presented of the potential applications of superconductive devices to electric power systems. Areas of principal interest include high-capacity transmission, energy storage, and power generation by rotating machinery, magneto-hydrodynamics and nuclear fusion. Some elements of superconductivity are discussed, including the properties of appropriate materials; these superconductive devices vis-à-vis the conventional counterparts in terms of reduction of power losses, decreased weight and size, and increased current capacity. An assessment is made of the time frame and the possibilities for introduction of superconductive devices into power systems.     

锂离子电池高镍三元正极材料LiNi1-x-yCoxMnyO2的改性研究进展

新能源产业的快速发展对储能材料与器件的综合性能提出了更高的要求。锂离子电池正极材料,尤其是高镍三元材料（LiNi_1-x-yCo_xMn_yO₂）具有高能量密度、高工作电压及优异的化学稳定性等特点,因而被认为是下一代动力电池商业化正极材料的优越选择。系统总结了高镍三元材料LiNi_1-x-yCo_xMn_yO₂的优势并指出了其亟待解决的问题;在此基础上,综述了其各类改性方法,包括各类阴阳离子掺杂、表面包覆、浓度梯度材料设计以及石墨烯复合等方法;最后对其发展方向及商业化应用进行了展望。     

Atomistic calculations of the electronic, thermal, and thermoelectric properties of ultra-thin Si layers

Low-dimensional semiconductors are considered promising candidates for thermoelectric applications with enhanced performance because of a drastic reduction in their thermal conductivity, κ _l , and possibilities of enhanced power factors. This is also the case for traditionally poor thermoelectric materials such as silicon. This work presents atomistic simulations for the electronic, thermal, and thermoelectric properties of ultra-thin Si layers of thicknesses below 10 nm. The Linearized Boltzmann theory is coupled: (i) to the atomistic sp³d⁵s^? tight-binding (TB) model for the electronic properties of the thin layers, and (ii) to the modified valence-force-field method (MVFF) for the calculation of the thermal conductivity of the thin layers. We calculate the room temperature electrical conductivity, Seebeck coefficient, power factor, thermal conductivity, and ZT figure of merit of ultra-thin p-type Si layers (UTLs). We describe the numerical formulation of coupling TB and MVFF to the linearized Boltzmann transport formalism. The properties of UTLs are highly anisotropic, and optimized thermoelectric properties can be achieved by the choice of the appropriate transport and confinement orientations, as well as layer thickness.     

Conduction mechanism in antiferrolectric PbZrO3 thin films—analysis of charge carrier trapping phenomenon

Abstract

Antiferroelectric compositions, such as PbZrO₃, are attractive candidates in charge storage devices and actuator/transducer applications in MEMs technology. Thin films of PbZrO₃were deposited on Pt coated Si substrates by a pulsed excimer ablation process. The process of field induced ferroelectric phase switching involves the domain wall reorientation in the polycrystalline thin films. The presence of grain boundaries and various defects in the polycrystalline thin films acts as the pinning sources for the various domain walls. These defects capture the charge carriers in the presence of external applied field and hinders further switching of the dipoles in the domains, thereby increases the response times and threshold voltages for the devices operations. Understanding of the trapping phenomenon in these films is very essential. Using Lampert's theory of space charge limited conduction both shallow and deep trap energies were estimated approximately from charge transport analysis.     

Problems of designing radioisotope thermoelectric power generators with a service life of decades for use in outer space exploration vehicles

The present work deals with the feasibility of developing a radioisotope thermoelectric power generator (RTPG) capable of operating unattended in outer space over a period of several decades, among other things, on the basis of chemical compounds that occur in meteoric matter. The possibilities for solving problems related to the production of three-dimensional materials and to thermoelement interconnections are discussed. The implementation of nanotechnology will allow one to achieve an increase in the efficiency of a RTPG by 15% and higher.     

固体电蓄热技术研究现状及展望

固体电蓄热技术能够将富余的低谷电转化为热能,对电网的深度调峰、弃风电量的利用及环境保护等方面具有十分重要的意义。在综述国内外固体电蓄热技术研究现状的基础上,从系统形式、固体蓄热材料、蓄热装置的结构和蓄/释热性能、运行方式和控制策略、经济性分析等方面介绍了固体电蓄热技术的研究进展,接着总结了国内外典型固体电蓄热装置的应用,最后结合固体电蓄热技术的发展要求,提出了相应的展望,为今后的研究和应用提供参考。     

Renewable Energy Devices and Systems – State-of-the-Art Technology,Research and Development,Challenges and Future Trends

Abstract

In this paper, essential statistics demonstrating the increasing role of renewable energy generation are firstly discussed. A state of the art review section covers fundamentals of wind turbines and PV systems. Included are schematic diagrams illustrating the main components and system topologies and the fundamental and increasing role of power electronics as an enabler for renewable energy integration, and for the future power system and smart grid. Recent examples of research and development, including new devices and system installations for utility power plants, as well for as residential and commercial applications are provided. Fuel cells, solar thermal, wave generators, and energy storage systems are also briefly presented and illustrated. Challenges and future trends for 2025 are summarized in a table for on-shore and off-shore wind energy, solar power, including photovoltaic and concentering, wave energy, fuel cells, and storage with batteries and hydrogen, respectively. Recommended further readings on topics of electric power engineering for renewable energy are included in a final section. This paper also represents an editorial introduction for two special issues of the Electric Power Component and Systems Journal, 43(8–10) and 43(12), respectively.     

A study of flexible piezoelectric generators by sputtering ZnO thin film on PET substrate

Abstract

Flexible technology has recently received much attention in the field of flexible sensors, wearable electronic devices, flexible transparent displays, and energy harvesters. Zinc oxide (ZnO) thin film is the preferred material for use in flexible devices due to its environmental friendliness, high electrical performance and low synthesis temperature. In addition, ZnO possesses a non-centrosymmetric crystal structure, causing a piezoelectric effect in the material. This work presents the fabrication of flexible piezoelectric generators using the deposition of ZnO on a PET substrate using sputtering techniques. The fabricated flexible generators are capable of generating an output power of 14 µW through an optimal resistive load of 750 kΩ. An output voltage of 2.00 Vp and a current of 150 μA measured across a 750 kΩ resistor were subsequently obtained.     

Ferroelectric materials and IR bolometer arrays: From hybrid arrays towards integration

Abstract

Large arrays of bolometer elements offer uncooled and simple operation, and a thermal imaging performance which challenges the cooled semiconductor (photon) detectors. A hybrid array technology, exploiting the pyroelectric property of ferroelectric ceramic materials in the bolometer elements, is the basis of a successful range of linear and 2-D arrays. However, other technologies will compete for cost effectiveness in large area devices. Direct integration of ferroelectric thin films onto suitable thermal microstructures on the silicon readout IC is attractive if deposition processes which are compatible with the silicon IC are established. Deposited lead based perovskite films show considerable potential. Thin film resistance bolometers will also compete, and have some advantages of compatibility in fabrication.     

SCALE FACTORS FOR PHYSICAL MODELLING OF MAGNETIC DEVICES

ABSTRACT

This paper investigates some of the potentialities and limitations of the technique of scale modelling as it applies to magnetic field problems. Simple relations for modelling static and dynamic linear devices are presented first. Particular attention is then given to the problem of scale modelling of nonlinear ferromagnetic devices. While static nonlinear fields can usually be modelled with good accuracy, time-varying fields in nonlinear ferromagnetic materials have severe modelling limitations.     

新型微温差电池的设计

将纳米材料的高效温差电转化性能和IC(集成电路)制造技术的长处相结合,设计出了一种全新结构的微型温差电池,这种全新结构的微型温差电池采用以多孔氧化铝模板为载体的n型和p型纳米线阵列温差电材料构成,其独特的层状结构有效地发挥了纳米线温差电材料的高效温差电转换性能,它通过将纳米线先并联再串联的方式使微型温差电池获得极高的电压输出,微型温差电池的厚度不超过100μm。     

Influence of the calcination procedure on the thermoelectric properties of calcium cobaltite Ca<Subscript>3</Subscript>Co<Subscript>4</Subscript>O<Subscript>9</Subscript>

Calcium cobaltite is one of the most promising oxide p-type thermoelectric materials. The solid-state reaction (or calcination, respectively), which is well known for large-scale powder synthesis of functional materials, can also be used for the synthesis of thermoelectric oxides. There are various calcination routines in literature for Ca₃Co₄O₉ powder synthesis, but no systematic study has been done on the influence of calcination procedure on thermoelectric properties. Therefore, the influence of calcination conditions on the Seebeck coefficient and the electrical conductivity was studied by modifying calcination temperature, dwell time, particle size of raw materials and number of calcination cycles. This study shows that elevated temperatures, longer dwell times, or repeated calcinations during powder synthesis do not improve but deteriorate the thermoelectric properties of calcium cobaltite. Diffusion during calcination leads to idiomorphic grain growth, which lowers the driving force for sintering of the calcined powder. A lower driving force for sintering reduces the densification. The electrical conductivity increases linearly with densification. The calcination procedure barely influences the Seebeck coefficient. The calcination procedure has no influence on the phase formation of the sintered specimens.