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A recent progress on thermoelectricsfrom Prof. Jiaqing He’s group, named Superior Thermoelectric Performance inPbTe-PbS Pseudo-binary: Extremely Low Thermal Conductivity and ModulatedCarrier Concentration, was published in Energy& Environmental Science (IF=15.49). This work is a further step overtheir last results published in Nature Communication (5,4515,2014).
Thermoelectricmaterials can directly create electrical power from heat and have thus drawngrowing research interest for decades.Lead chalcogenides are dominant thermoelectric materials in themedium-temperature range, owing to their highly favorable electronic bandstructures and low thermal conductivities achievable. An important system isthe PbTe-PbS pseudo-binary and its low thermal conductivity originates largelyfrom the coexistence of both alloying and nanostructuring throughphase-separation. In this work, they systematically studied, via transmission electron microscopyobservations and theoretical calculations, samples of Spark Plasma Sintered(SPSed) Na over-doped (PbTe)1-x(PbS)x. The highest figure ofmerit, viz., ZT~ 2.3 was obtained at 923 K, when the PbS phase-fraction, x, was 20%, corresponding to the lowestlattice thermal conductivity of the series. They found that the consistentlylower lattice thermal conductivities in the SPSed samples as compared with thecorresponding ingots, originating from the mesostructured nature of the former,contributes significantly to the superior ZT.They also studied the onset of carrier concentration modulation ~600 K, whichleads to the observed saturation of electrical transport properties due to thediffusion and re-dissolution of excessive Na into the PbTe-PbS matrix. It isbelieved that this carrier concentration modulation is equally crucial toachieve the very high power factors and the outstanding thermoelectricperformances in SPSed PbTe-PbS binaries.