Abstract
Maximizing band degeneracy and minimizing phonon relaxation time are proven to be successful for advancing thermoelectrics. Alloying with monotellurides has been known to be an effective approach for converging the valence bands of PbTe for electronic improvements, while the lattice thermal conductivity of the materials remains available room for being further reduced. It is recently revealed that the broadening of phonon dispersion measures the strength of phonon scattering, and lattice dislocations are particularly effective sources for such broadening through lattice strain fluctuations. In this work, a fine control of MnTe and EuTe alloying enables a significant increase in density of electron states near the valence band edge of PbTe due to involvement of multiple transporting bands, while the creation of dense in-grain dislocations leads to an effective broadening in phonon dispersion for reduced phonon lifetime due to the large strain fluctuations of dislocations as confirmed by synchrotron X-ray diffraction. The synergy of both electronic and thermal improvements successfully leads the average thermoelectric figure of merit to be higher than that ever reported for p-type PbTe at working temperatures.
Highlights
Driven by energy crisis and the resultant environmental issues, interests in advancing clean energy technologies have grown rapidly in this century
The well-improved electronic performance enabled by converged valence bands and the significantly reduced κL due to dislocations induced lattice strain fluctuations, synergistically lead to an extraordinary thermoelectric performance
Shown in Figure S1, observable diffraction peaks can be well indexed to the rock salt structure of PbTe
Summary
Driven by energy crisis and the resultant environmental issues, interests in advancing clean energy technologies have grown rapidly in this century. Based on either Seebeck or Peltier effect, thermoelectrics have important applications in energy harvesting, refrigeration, and thermal sensing, due to the capability of a direct conversion between heat and electricity [1,2,3]. To enable a widespread application, the conversion efficiency needs to be maximized, which requires thermoelectric materials to have a high figure of merit zT = S2σT/ðκE + κLÞ. S, σ, T, κE, and κL are the Seebeck coefficient, electrical conductivity, absolute temperature, and electronic and lattice components of the thermal conductivity, respectively [4]. ZT can be maximized when both electronic transport properties and lattice thermal conductivity are fully optimized [5,6,7]. A great deal of efforts have been devoted to decoupling these parameters for an effective enhancement in power factor S2σ, and successful strategies are typified by engineering the band structure for a high band degeneracy [8,9,10,11], a low electron inertial mass [12], and a weak charge scattering [13], which has been demonstrated in various thermoelectrics [4, 14,15,16,17,18,19]
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