14 research outputs found
Key issues in development of thermoelectric power generators: High figure-of-merit materials and their highly conducting interfaces with metallic interconnects
Thermoelectric generators (TEGs) are devices that convert temperature differences into electrical energy, which work on the thermoelectric phenomena known as Seebeck effect. The thermoelectric phenomena have widely been used for heating and cooling applications, however electric power generation has only been limited to niche applications e.g. thermoelectric power generators for space missions. TEG provides one of cleanest energy conversion method, which is noise-free, virtually maintenance free and can continuously produces power for several years under ambient conditions. In recent years, energy generation through thermoelectric harvesting has witnessed an increased interest for various applications, including tapping waste heat from the exhaust of vehicles, from industries, etc. The development of an efficient TEG requires the fulfillment of several factors, which includes availability of n- and p-type thermoelectric materials with high figure-of-merit (ZT), preparation of ohmic contacts between thermoelements and metallic interconnects and management of maximum heat transfer though the device. In this review, we present an overview on the various aspects of device development i.e. from synthesis of high ZT thermoelectric materials to issues & design aspects of the TEG. A discussion on the various strategies employed to improve ZT is described. It is shown that a ZT of >2 has widely been reported in literature, which has been achieved either by enhancing the power factor and/or reducing the thermal conductivity of the materials. A discussion on the status on the development of TEGs suitable for operation at different temperature ranges i.e. 650 degrees C is presented. Finally, the cost of fabrication of TEGs and their potential applications in different areas have been highlighted
Synthesis & Tailoring the Thermal Conductivity of Sr Doped Bi2Se3 Thermoelectric Material
We have investigated the thermal transport properties of SrxBi(2)-xSe(3) (x=0, 0.05, 0.2). The samples were synthesized by melt route method followed by vacuum hot press. The structural and morphological information of sample has been retrieved using x-ray diffraction (XRD) and scanning electron microscopy (SEM). The thermal transport measurement were performed in the temperature range of 300-550 K. It is found that with increasing Sr content the total thermal conductivity of the material decreases which is attributed to the enhance phonon scattering due to natural grown layered structure and defect induced by Sr doping
Synthesis & Tailoring the Thermal Conductivity of Sr Doped Bi2Se3 Thermoelectric Material
We have investigated the thermal transport properties of SrxBi(2)-xSe(3) (x=0, 0.05, 0.2). The samples were synthesized by melt route method followed by vacuum hot press. The structural and morphological information of sample has been retrieved using x-ray diffraction (XRD) and scanning electron microscopy (SEM). The thermal transport measurement were performed in the temperature range of 300-550 K. It is found that with increasing Sr content the total thermal conductivity of the material decreases which is attributed to the enhance phonon scattering due to natural grown layered structure and defect induced by Sr doping
Transition from n- to p-type conduction concomitant with enhancement of figure-of-merit in Pb doped bismuth telluride: Material to device development
The majority of industrial, automobile processes, electrical appliances emit waste heat in the low-temperature range (<573 K), hence efficient thermoelectric materials operating in this range are highly needed. Bismuth telluride (Bi2Te3) based alloys are conventional thermoelectric material for the low-temperature application. The pure Bi2Te3 sample synthesized in this work exhibits n-type conduction. We demonstrate that by small doping of Pb at Bi site a transition in electrical transport form n- to p-type is observed. The figure-of-merit (ZT) of n-type Bi2Te3 is similar to 0.47 and optimized Bi1.95Pb0.05Te3 exhibit p-type conduction with enhanced ZT of similar to 0.63 at 386 K. The conversion efficiency of Bi1.95Pb0.05Te3 based single thermoelement with hot pressed Ni/Ag electrical contacts was found to be similar to 4.9% for a temperature difference (Delta T) of 200 K. The efficiency was further enhanced to similar to 12% (at Delta T similar to 494 K) in the segmented thermoelement consisting of Bi1.95Pb0.05Te3 and (AgSbTe2)(0.15)(GeTe)(0.85) (i.e. TAGS-85
Transition from n- to p-type conduction concomitant with enhancement of figure-of-merit in Pb doped bismuth telluride: Material to device development
The majority of industrial, automobile processes, electrical appliances emit waste heat in the low-temperature range (<573 K), hence efficient thermoelectric materials operating in this range are highly needed. Bismuth telluride (Bi2Te3) based alloys are conventional thermoelectric material for the low-temperature application. The pure Bi2Te3 sample synthesized in this work exhibits n-type conduction. We demonstrate that by small doping of Pb at Bi site a transition in electrical transport form n- to p-type is observed. The figure-of-merit (ZT) of n-type Bi2Te3 is similar to 0.47 and optimized Bi1.95Pb0.05Te3 exhibit p-type conduction with enhanced ZT of similar to 0.63 at 386 K. The conversion efficiency of Bi1.95Pb0.05Te3 based single thermoelement with hot pressed Ni/Ag electrical contacts was found to be similar to 4.9% for a temperature difference (Delta T) of 200 K. The efficiency was further enhanced to similar to 12% (at Delta T similar to 494 K) in the segmented thermoelement consisting of Bi1.95Pb0.05Te3 and (AgSbTe2)(0.15)(GeTe)(0.85) (i.e. TAGS-85)
Transition from n- to p-type conduction concomitant with enhancement of figure-of-merit in Pb doped bismuth telluride: Material to device development
The majority of industrial, automobile processes, electrical appliances emit waste heat in the low-temperature range (<573 K), hence efficient thermoelectric materials operating in this range are highly needed. Bismuth telluride (Bi2Te3) based alloys are conventional thermoelectric material for the low-temperature application. The pure Bi2Te3 sample synthesized in this work exhibits n-type conduction. We demonstrate that by small doping of Pb at Bi site a transition in electrical transport form n- to p-type is observed. The figure-of-merit (ZT) of n-type Bi2Te3 is similar to 0.47 and optimized Bi1.95Pb0.05Te3 exhibit p-type conduction with enhanced ZT of similar to 0.63 at 386 K. The conversion efficiency of Bi1.95Pb0.05Te3 based single thermoelement with hot pressed Ni/Ag electrical contacts was found to be similar to 4.9% for a temperature difference (Delta T) of 200 K. The efficiency was further enhanced to similar to 12% (at Delta T similar to 494 K) in the segmented thermoelement consisting of Bi1.95Pb0.05Te3 and (AgSbTe2)(0.15)(GeTe)(0.85) (i.e. TAGS-85)
Tellurium-free thermoelectrics: Improved thermoelectric performance of n-type Bi2Se3 having multiscale hierarchical architecture
We report an improved thermoelectric performance of n-type Bi2Se3 bulk alloys synthesized by vacuum melt method followed by vacuum hot-pressing. In the samples so prepared, the synergetic combination of ultra low thermal conductivity (similar to 0.7 W/m K), high Seebeck coefficient (similar to-168 mu V/K), and low electrical resistivity (similar to 15 mu Omega-m) has been observed to successfully lead to a high figure-of-merit (ZT) of similar to 0.96 at 370 K. A detailed characterization of the samples reveals a presence of multiscale hierarchical defect structures i.e. atomic scale disorder arising from a multitude of factors such as large anharmonicity of Bi-Se bond due to electrostatic repulsion between the lone pair of Bi and charge of Se, nanoscale grains and dislocations trapped between mesoscale grains/grain boundaries accompanied by intrinsic layered structure of Bi2Se3. This compact layered grain structure in its consequence offers a high charge carrier mobility and thereby results into a high power factor, while multiscale hierarchical architecture accounts for the scattering of a wider spectrum of phonons leading to an ultra low thermal conductivity. In view of this promising thermoelectric performance together with the presence of copiously available constituent namely Se, the hot-pressed Bi2Se3 presents a technologically suitable and commercially viable alternative to the conventional Bi2Te3 which is based on expensive and scarcely available Te