The effect of Ag concentration on the structural, electrical and thermal transport behavior of Pb:Te:Ag:Se mixtures and improvement of thermoelectric performance via Cu doping

Pb, Te, Ag and Se, when reacted in a 1:1:x:1 (x = 1.9, 2.0, 2.01) molar ratio, form a two phase composite which consists of a phase which crystallizes in the fcc cubic PbSe structure and a phase that crystallizes in the Ag2Te structure. In this article, we demonstrate that by varying the Ag concentration, we can manipulate which variant of the Ag2Te structure stabilizes at room temperature (monoclinic α-Ag2Te or cubic β-Ag1.9Te) and can consequently manipulate the electrical and thermal transport behavior of the composite and hence the thermoelectric performance. Additionally, we show that Cu-doping results in an overall improvement in thermoelectric performance. Our results suggest that formation of composites is a viable path for achieving a phonon-glass-electron-crystal (PGEC) alloy.

Research highlights▶ Pb, Te, Ag and Se, when reacted in a 1:1:x:1 (x = 1.9, 2.0, 2.01) molar ratio, form a two phase composite which consists of a phase which crystallizes in the fcc cubic PbSe structure and a phase that crystallizes in the Ag2Te structure. ▶ In this article, we demonstrate that by varying the Ag concentration, we can manipulate which variant of the Ag2Te structure stabilizes at room temperature (monoclinic α-Ag2Te or cubic β-Ag1.9Te) and can consequently manipulate the electrical and thermal transport behavior of the composite and hence the thermoelectric performance. ▶ Additionally, we show that Cu-doping (Pb:Te:Ag:Cu:Se, 1:1:x:y:1, x = 1.8 y = 0.1, x = 1.85 y = 0.05) results in an overall improvement in thermoelectric performance. ▶ Specifically, we observed a 20% (0.45–0.54) increase in ZT in the case of the x = 1.8 y = 0.1 sample, when compared to the non-Cu doped samples. Our results suggest that formation of composites is a viable path for achieving a phonon-glass-electron-crystal (PGEC) alloy i.e. an alloy with very low thermal conductivity and favorable electrical conductivity.