Melt-Spun SiGe Nano-Alloys: Microstructural Engineering Towards High Thermoelectric Efficiency
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https://doi.org/10.1007/s11664-020-08560-6 Ó 2020 The Minerals, Metals & Materials Society
Melt-Spun SiGe Nano-Alloys: Microstructural Engineering Towards High Thermoelectric Efficiency AVINASH VISHWAKARMA,1,2 NAGENDRA S. CHAUHAN RUCHI BHARDWAJ,1,2 KISHOR KUMAR JOHARI,1,2 SANJAY R. DHAKATE,1,2 BHASKER GAHTORI,1,2,5 and SIVAIAH BATHULA 1,2,4,6
,3
1.—Academy of Scientific and Innovative Research (AcSIR), Ghaziabad, Uttar Pradesh 201002, India. 2.—Division of Advanced Materials and Devices Metrology, CSIR-National Physical Laboratory, Dr. K. S. Krishnan Marg, New Delhi 110012, India. 3.—Micro and Nanofabrication Department, International Iberian Nanotechnology Laboratory, Braga 4715-330, Portugal. 4.—School of Minerals, Metallurgical and Materials Engineering, IIT Bhubaneswar, Bhubaneswar 752050, Odisha, India. 5.—e-mail: [email protected]. 6.—e-mail: [email protected]
Silicon-germanium (SiGe) alloys are prominent high-temperature thermoelectric (TE) materials used as a powering source for deep space applications. In this work, we employed rapid cooling rates for solidification by melt-spinning and rapid heating rates for bulk consolidation employing spark plasma sintering to synthesize high-performance p-type SiGe nano-alloys. The current methodology exhibited a TE figure-of-merit (ZT) 0.94 at 1123 K for a higher cooling rate of 3.0 9 107 K/s. This corresponds to 88% enhancement in ZT when compared with currently used radioisotope thermoelectric generators (RTGs) in space flight missions, 45% higher than pressure-sintered p-type alloys, which results in a higher output power density, and TE conversion efficiency (g) 8% of synthesized SiGe nano-alloys estimated using a cumulative temperature dependence (CTD) model. The ZT enhancement is driven by selective scattering of phonons rather than of charge carriers by the high density of grain boundaries with random orientations and induced lattice-scale defects, resulting in a substantial reduction of lattice thermal conductivity and high power factor. The TE characteristics of synthesized alloys presented using the constant property model (CPM) and CTD model display their high TE performance in high-temperature regimes along with wide suitability of segmentation with different mid-temperature TE materials.
(Received June 11, 2020; accepted October 9, 2020)
Vishwakarma, Chauhan, Bhardwaj, Johari, Dhakate, Gahtori, and Bathula
Graphic Abstract
Key words: SiGe alloys, lattice thermal conductivity, melt-spun, rapid solidification, spark plasma sintering
INTRODUCTION Thermoelectric (TE) technology has a long history of providing simple and reliable power generation solutions for increasing the energy efficiency of various industrial processes and providing power in remote applications (space probes, space stations). The success of radioisotope thermoelectric generators (RTGs) as safe, reliable, long-lived power systems in space exploration missions had motivated the future expansion of TE technology in terrestrial applications, specifically in the area
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