Enhancement of thermoelectric properties by effective K-doping and nano precipitation in quaternary compounds of (Pb_1−xK_xTe)_0.70(PbSe)_0.25(PbS)_0.05

Abstract

We investigated thermoelectric properties in K-doped quaternary compounds of (Pb1-xKxTe)0.70(PbSe)0.25(PbS)0.05 (x ≤ 0.03). In terms of two valence bands model, we argue that the L-band approaches to the Σ-band with increasing the K-doping concentration resulting in the increase of carrier concentration and effective mass of carrier due to the increase of band degeneracy. The effective K-doping by x = 0.02 and PbS substitution causes high power factor and low thermal conductivity, resulting in the comparatively high ZT value of 1.72 at 800 K. The low thermal conductivity for (Pb0.98K0.020Te)0.70(PbSe)0.25(PbS)0.05 compound is attributed from the lattice distortion and line dislocation in a phase of nano precipitation. By optimizing K-doping and PbS substitution, we achieved the enhancement of practical thermoelectric performance such as average ZTavg = 1.08, engineering (ZT)eng = 0.81, maximum efficiency ηmax = 11.63 %, and output power density Pd = 6.3 W cm -2 , with temperature difference ΔT = 500 K, which has practical applicability in waste heat power generation technologies.

Synergetic Approach for Superior Thermoelectric Performance in PbTe-PbSe-PbS Quaternary Alloys and Composites

“…Energies 2020, 13, 72 4 of 29 The lattice parameters of PbTe, PbSe, and PbS are 3.22, 3.07, and 2.965 Å , respectively, along the (200) plane [31,32]. Numerous nanoprecipitates are also found in K-doped (Pb0.98K0.02Te)0.7(PbSe)0.25(PbS)0.05 [7] and Cl-doped (PbTe0.93−xSe0.07Clx)0.93(PbS)0.07 ( = 0.0005) [11], which are synthesized by same process with (PbTe)0. 75 Figures 3d and 4f, respectively.…”

“…The limited SrTe doping is segregated in the PbTe matrix, resulting in nanoprecipitations [32]. In PbTe-PbSe-PbS quaternary alloys, the miscibility gap between the PbTe and PbS phase is expected in the thermodynamic phase diagram, implying phase separation via metastable nucleation during grain growth or spinodal decomposition of nanoprecipitates [33] because the thermodynamic nanoscale precipitation of PbS in the PbTe-PbSe matrix is likely [7,31,34].…”

“…In order to identify the phase of the nanoprecipitates, elemental analysis is reported by energy dispersive X-ray spectroscopy (EDS) in (Pb 0.98 K 0.02 Te) 0.7 (PbSe) 0.25 (PbS) 0.05 [7], as shown in Figure 5. Figure 5a,b show the nanoprecipitates and phase boundary due to spinodal decomposition, displayed as the dark region.…”

“…The thermoelectric performance of PbTe-based materials has been improved significantly through electronic structure modifications [3][4][5][6]. Semiconductor PbTe of p-type can be produced by doping with Tl, Na, and K on Pb sites [5,[7][8][9][10]. On the other hand, n-type PbTe can be produced by Cl doping on the Te site [11].…”

“…Experimental and theoretical lattice thermal conductivity, κ L , of Pb 0.98 K 0.02 Te (closed black squares and pink triangles) and and Pb 0.98 K 0.02 Te 0.7 Se 0.25 S 0.05 (open black squares and pink triangles).Reproduced with permission from[7], copyright 2016 the Royal Society of Chemistry.…”