PbTe-based thermoelectric materials are promising for mid-temperature waste heat recovery, yet n-type PbTe underperforms its p-type counterpart. Herein, high-performance n-type PbTe is achieved through I/Ge co-doping and in-situ composite engineering with Sb 2 Te 3 prepared by melting combined spark plasma sintering. Sb 2 Te 3 alloying introduce in-situ formed Sb/Sb 2 Te 3 precipitates. Furthermore, iodine doping optimizes the carrier concentration to ∼3.4 × 10 19 cm –3 , boosting the room-temperature electrical conductivity to ∼1404 S cm −1 and yielding a high power factor of ∼17.4 μW cm −1 K −2 for the PbTe-Sb 2 Te 3 sample. Meanwhile, lattice thermal conductivity is synergistically suppressed to ∼0.37 W m –1 K –1 at 673 K through Ge-induced point defects/off-center anharmonicity and Sb/Sb 2 Te 3 precipitates. This synergistic strategy results in a peak ZT of ∼1.30 at 823 K and a high average ZT of ∼0.91 at 323–823 K. This work demonstrates that synergistic I/Ge co-doping and composite precipitation effectively enhance thermoelectric performance in n-type PbTe.
Based on the calculated results of band structures and density of states, Bi doping is used to adjust its carrier concentration in order to obtain n-type PbTe materials with high power factor. Then, coherent nanophase Cu 1.75 Te is in situ formed in the n-type PbTe matrix, which can simultaneously optimize the thermal and electrical properties. As a result, at a relative lower temperature than other reports, the highest ZT value of 1.4 is obtained at 623 K for the nominal Pb 0.995 Bi 0.005 Te+0.86 wt% Cu 1.75 Te sample. More importantly, the ZT hold a higher value in the broad temperature; especially, ZT value is about 1.2–1.4 in the temperature range of 573–773 K, which is beneficial to the significant average ZT value ZT ave ∼ 0.9 in the temperature range of 300–773 K. These results indicate that it is an effective and feasible method to enhance the thermoelectric properties via synergistic modulation of electrical and thermal transport properties by element doping and in situ coherent nanophase.
Realizing high average thermoelectric figure of merit (ZT ave ) and power factor (PF ave ) has been the utmost task in thermoelectrics. Here the new strategy to independently improve constituent factors in ZT is reported, giving exceptionally high ZT ave and PF ave in n-type PbSe. The nonstoichiometric, alloyed composition and resulting defect structures in new Pb 1+ x Se 0.8 Te 0.2 ( x = 0–0.125) system is key to this achievement. First, incorporating excess Pb unusually increases carrier mobility ( µ H ) and concentration ( n H ) simultaneously in contrast to the general physics rule, thereby raising electrical conductivity ( σ ). Second, modifying charge scattering mechanism by the authors’ synthesis process boosts a magnitude of Seebeck coefficient ( S ) above theoretical expectations. Detouring the innate inverse proportionality between n H and µ H ; and σ and S enables independent control over them and change the typical trend of PF to temperature, giving remarkably high PF ave ≈20 µW cm −1 K −2 from 300 to 823 K. The dual incorporation of Te and excess Pb generates unusual antisite Pb at the anionic site and displaced Pb from the ideal position, consequently suppressing lattice thermal conductivity. The best composition exhibits a ZT ave of ≈1.2 from 400 to 823 K, one of the highest reported for all n-type PbQ (Q = chalcogens) materials.
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