Effect of double doping, Li and Se, on the high-temperature thermoelectric properties of Cu 2 Te
- PDF / 1,782,526 Bytes
- 6 Pages / 595.276 x 790.866 pts Page_size
- 97 Downloads / 152 Views
Effect of double doping, Li and Se, on the high‑temperature thermoelectric properties of Cu2Te Md. Mofasser Mallick1 · Satish Vitta2 Received: 9 December 2019 / Accepted: 20 January 2020 © Springer Science+Business Media, LLC, part of Springer Nature 2020
Abstract Cuprous chalcogenide, Cu2Se, attracted attention due to its large Seebeck coefficient coupled with low thermal conductivity, facilitated by the presence of disordered Cu-ions in the structure of Cu–Se. This compound is thermally unstable prompting investigation of its analogue C u2Te which has a lower figure-of-merit zT due to its high charge carrier concentration. In the present work, a dual substitution, both cation and anion by Li and Se, respectively, has been attempted to enhance zT. The Cu2−xLixTe1−ySey alloys have been synthesized by a simple, conventional arc melting process and investigated without subjecting to any further processing. The room temperature microstructure shows a plate-like layered nanostructure in the grains with the grains oriented in random directions. The alloys at room temperature have two polymorphic phases, superstructured hexagonal and orthorhombic, co-existing in all the alloys. The alloys exhibit a degenerate semiconducting behavior in the range 300–1000 K with the conductivity decreasing from ~ 3000 Scm−1 to 700 S cm−1. All the alloys show a hole dominant −1 Seebeck coefficient which increases with temperature from ~ 30 to 135 μVK . The alloy with dual substitution, Li-0.1 and Se-0.03, has the highest power factor of 1.6 m Wm−1 K−2 at 1000 K. It’s low thermal conductivity in the complete range 300% by introducing up to 50 wt% of Ag2Te in Cu2Te, which is primarily due to reduction in charge carrier concentration [19]. A zT value of ⁓1 has been achieved in In-substituted Cu2Te by alloying it with pristine compound [20]. Apart from improving zT value, low cost and facile synthesis processes of synthesizing thermoelectric materials are also important. In general, synthesis processes of single-phase chalcogenides happen to be rigorous and time taking [15]. At first, elements in stoichiometric ratio are melted followed by annealing of the ingot for a long period of time in a vacuum-sealed quartz tube. The ingot then is ground into powder and consolidated into pellets using spark plasma sintering at high pressure. A modified one-step synthesis of chalcogenides using arc melting technique would be much faster and cost effective. In the present work, a dual substitution strategy has been used together with simple and minimal processing to increase the figure-of-merit. The divalent Cu has been substituted with monovalent Li, while Te has been partially substituted with isoelectronic Se. The monovalent Li is highly electropositive compared to Cu and hence results in an increase in ionic character of bonding between Li and Te. This should lead to a decrease in effective charge carriers and thus decrease electrical and thermal conductivity while enhancing the Seebeck coefficient. This effect is anticipated to be more
Data Loading...
