Percolation Process-Mediated Rich Defects in Hole-Doped PbSe with Enhanced Thermoelectric Performance

Abstract

PbSe–SnSe solid solutions have been extensively investigated in the fields of topological physics, optoelectronic conversion, and thermoelectric technology. In this study, we show that minute Sn-doped Pb0.98Na0.02Se behaves quite differently from conventional solid solutions. A dilute amount of Sn dopants induces rich defects (substitutional Sn atoms, interstitial Sn atoms, and cation vacancies) in hole-doped PbSe. Moreover, with growing concentration of Sn, the dominated defect type varies accordingly due to the percolation process of dopants, leading to anomalies in the dependences of thermoelectric properties on compositions. These rich defects increase the thermoelectric performance of p-type PbSe by (i) enhancement of Seebeck coefficient through increased density of states by interstitial Sn atoms; (ii) reduction of lattice thermal conductivity through strong point defect scattering mostly contributed by interstitial Sn atoms and cation vacancies. Moreover, the dynamic migrations of Sn atoms from the interstitial sites to regular lattice sites at elevated temperatures (>623 K) give rise to diffusion-like atomic vibrations that frustrate heat conduction further. Consequently, 1 mol % Sn doping in Pb0.98Na0.02Se yields 20% improvement of thermoelectric performance. This work demonstrates that dilute doping-induced percolation phenomena should be taken into consideration when developing efficient thermoelectric materials.

Defect Reconfiguration in Hole-Doped PbSe via Minute Te Doping for Significantly Enhanced Thermoelectric Performance

“…As discussed in our previous report, when Sn is doped into p-type PbSe in a dilute amount, it triggers the percolation process and induces rich defects, leading to the formation of Sn 4+ and Sn 2+ . 16 The Sn 4+ ion has a smaller size of 0.69 Å than ∼1.07 Å of tetrahedral interstices in PbSe and is easy to enter interstices. 16,31,32 Therefore, an equal amount of Pb vacancies remains.…”

“…As described in our previous work, the abrupt decrease of κ lat at 673 K in the x = 0 sample results from the dynamic migration of interstitial Sn atoms to Pb vacancies. 16 But in Te-doped samples, a large amount of interstitial Sn atoms were pulled back to Pb sublattice sites. The decline of the population of Sn i +4 in Te-doped samples leads to an extremely unapparent dynamic migration phenomenon at elevated temperatures, which is proved by TEC measurement in Figure S3.…”

“…Therefore, dilute Sn-doped Pb 0.98 Na 0.02 Se materials have the potential for achieving excellent thermoelectric performance. However, the Pb vacancies induced by interstitial Sn 4+ critically hinder the charged carrier transport, causing a quite low μ of ∼2.8 cm 2 V –1 s –1 at 300 K, preventing them from gaining outstanding ZT values . A maximum ZT value is only ∼1.2 at 873 K and achieved in the Pb 0.97 Sn 0.01 Na 0.02 Se sample.…”

“…12−15 Previous research proves that an extremely low κ lat of ∼0.37 W m −1 K −1 at 873 K and observable improvement of Seebeck coefficients were achieved in a dilute Sn-doped Pb 0.98 Na 0.02 Se system. 16 Therefore, dilute Sn-doped Pb 0.98 Na 0.02 Se materials have the potential for achieving excellent thermoelectric performance. However, the Pb vacancies induced by interstitial Sn 4+ critically hinder the charged carrier transport, causing a quite low μ of ∼2.8 cm 2 V −1 s −1 at 300 K, preventing them from gaining outstanding ZT values.…”

“…Unfortunately, because of the strong interdependence of thermoelectric transport parameters, excellent ZT is difficult to be achieved. − Apart from this, the advanced thermoelectric performance can also be designed by the quality factor B , which is expressed as follows: , B = 9 false( m false* false) 3 / 2 μ κ lat true( T 300 true) 5 / 2 where m * and μ denote the effective mass of free carrier and carrier mobility, respectively. Obviously, a high-performance thermoelectric material requires large m *, high μ, and low κ lat . − Previous research proves that an extremely low κ lat of ∼0.37 W m –1 K –1 at 873 K and observable improvement of Seebeck coefficients were achieved in a dilute Sn-doped Pb 0.98 Na 0.02 Se system . Therefore, dilute Sn-doped Pb 0.98 Na 0.02 Se materials have the potential for achieving excellent thermoelectric performance.…”