Tuning figure of merit in Na doped nanocrystalline PbSnTeSe high entropy alloy via band engineering

The new generation thermoelectric material research warrants novel composition tailoring and advanced processing to explore the commendable thermoelectric properties. In this context, the multi-component alloy design with engineered configuration entropy and band tuning approach is proposed for the nanocrystalline lead tin selenide telluride (PbSnTeSe) high entropy alloy (HEA) with sodium (Na) doping of concentrations 0.01 at.% and 0.02 at.% at different vacancy sites of Pb and Sn. The HEA samples were synthesized via mechanical alloying (MA) and spark plasma sintering (SPS). The first principle study using virtual crystal approximation (VCA) confirms that Na occupies Pb/Sn substitutional doping sites in the PbSnTeSe HEA. The complex chemical gradient tailoring through high entropy stabilization and nanostructuring favors the low thermal conductivity (<1.2W/mK). The substitutional doping of Na of 0.01 at.% in Pb site of PbSnTeSe HEA shows a significant effect in the band tuning, thereby increasing the absolute Seebeck coefficient (S) from 159.67 μV/K to 230 μV/K lead towards a high power factor of 15.18×10−4W/mK2. Thus, it results in a superior figure of merit (ZT) of 0.84 in nanocrystalline Pb0.99SnTeSe-Na0.01 HEA at 573K which is a commendable improvement of 182% than the PbSnTeSe pristine HEA (ZT=0.46).