Enhanced thermoelectric properties of n-type Ti-doped PbTe
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MRS Advances © 2019 Materials Research Society DOI: 10.1557/adv.2019.233
Enhanced thermoelectric properties of n-type Tidoped PbTe Ariel Loutati, Shir Zuarets, David Fuks and Yaniv Gelbstein Department of Materials Engineering, Ben-Gurion University of the Negev, Beer-Sheva, Israel.
Abstract
Thermoelectric (TE) generators, converting waste heat to electricity regain their attractiveness for reduction of fossil fuels’ reliance, and consequently minimizing adverse environmental effects. Such generators are based on an electrical series connection of TE couples, which consist n- and p- type semiconducting legs divided by metallic bridges. While for intermediate temperatures of up to 500oC, n-type PbTe was extensively studied and employed in commercial TE power generation applications, its maximal efficiency, as was reflected by the TE figure of merit, ZT, was in most of the cases maximized at a narrow temperature range for any given donor dopant concentration. The most commonly applied donor dopants are iodine and bismuth. Yet, some interesting characteristics were recently proposed upon using Ti as a donor dopant. Up to date an impressive maximal ZT of ~1.2 was obtained at 500oC, upon doping of PbTe by 0.1 at.% Ti, while no lower concentrations were ever investigated. In the current research a lower, 0.05 at.% Ti doping level was applied, leading to the highest ever reported ZT values, for any given Ti doped PbTe, up to 350 oC. Since the chemical compatibility of Ti with PbTe, as a metallic bridge in such couples, is well established, mainly due to its low diffusion rates, the potential of generating a stable Ti-doped functionally graded n-type PbTe material, with enhanced TE performance, is currently being proposed.
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INTRODUCTION In the recent years, thermoelectric (TE) generators, directly converting heat to electricity, regain their attractiveness not just as stand-alone devices in the automotive and aerospace applications, but also as a part of hybrid devices combined with other energy conversion technologies. Hybrid photovoltaic-thermoelectric (PV-TE) devices possess a potential of utilizing a wider range of the solar spectrum, compared to standard photovoltaic (PV) cells, utilizing mostly the visible and ultraviolet ranges, upon expending their effectiveness also in the infrared range [1,2]. Another noteworthy advantage of such hybridization, concerns with high temperatures solar applications, in which the PV efficiency is generally decreased with increasing the temperature, while that of the thermoelectric (TE) device, which is governed by Carnot efficiency, is generally increased, mitigating any high temperature efficiency reduction, upon using a hybrid PV-TE device [3]. Hybrid fuel cell-thermoelectric (FC-TE) devices show another advantage. The most efficient fuel
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