Lead Vacancy Promotes Sodium Solubility to Achieve Ultra‐High zT in Only Ternary Pb_1‐xNa_xTe

Abstract

Chemical doping of sodium is an indispensable means to optimize thermoelectric properties of PbTe materials, while a bottleneck is that an aliovalent atom doping leads to spontaneous intrinsic defects in the PbTe matrix, resulting in low dopant solubility. Therefore, it is urgent to improve the doping efficiency of Na for maximizing optimization. Here, an amazing new insight that the intentionally introduced Pb vacancies can promote Na solubility in ternary Pb1‐xNaxTe is reported. Experimental analysis and theoretical calculations provide new insights into the inherent mechanism of the enhancement of Na solubility. The Pb vacancies and the resultant more dissolved Na not only synergistically optimize the carrier concentration and further facilitate the band convergence, but also induce a large number of dense dislocations in the grains. Consequently, benefiting from the self‐enhancement of Seebeck coefficient and the minimization of lattice thermal conductivity, an 18% growth is obtained for the figure of merit zT in vacancy‐containing Pb0.95Na0.04Te sample, reaching maximum zTmax ≈ 2.0 at 823 K, which achieves an ultra‐high performance in only Na‐doped ternary Pb1‐xNaxTe materials. The strategy utilized here provides a novel route to optimize PbTe materials and represents an important step forward in manipulating thermoelectrics to improve dopant solubility.

Promoted Na Solubility and Modified Band Structure for Achieving Exceptional Average ZT by Extra Mn Doping in PbTe

“…In particular, the x = 0.04 sample exhibits an excellent S at both room temperature (∼114 μV K −1 at 303 K) and high temperature (∼281 μV K −1 at 823 K), which is also at the forefront in many p-type PbTe systems. 24,34,35 However, a deteriorating trend occurs in all Mn-containing samples after reaching 673 K, possibly due to the enhanced bipolar diffusion effect at elevated temperatures. Importantly, Mn doping in PbTe-or SnTe-based materials has been widely recognized for its effectiveness in promoting valence band convergence, which allows significant enhancement in S. 25,37,38 Based on this, the results of R H , which corresponding to ΔE L-∑ was analyzed and displayed in Figure 2d.…”

“…(a) μ w /κ lat and (b) ZT of Pb 0.95– x Na 0.04 Mn x Te. Comparison of the (c) temperature-dependent ZT and (d) average ZT avg with some high-performance Pb–Na–Te systems. ,,, …”

“…On the other hand, high-resolution S4b) can be attributed to the inevitable air exposure during the performance testing and characterization, which is commonly observed in PbTe-based systems. 24,28,31 The improved solubility of Na in Pb 0.95 Na 0.04 Te with extra Mn doping plays a dramatic role in the electric properties. Figure 2a shows a decreasing trend in the σ values of all assintered samples with increasing temperature, indicating a typical degenerate semiconductor behavior.…”

“…Recently, we have demonstrated that the active introduction of Pb vacancies can be effective in enhancing the solubility of Na in PbTe, and thus remarkable ZT max of ∼2.0 was obtained in only the ternary Pb 1−x Na x Te system. 24 Nevertheless, although a significant improvement in peak ZT can be realized, the average ZT (ZT ave ) is still at an unsatisfactory level, which is far from sufficient for practical applications. 25 In light of this, how to significantly enhance the average ZT of PbTe-based TE materials while maintaining its excellent ZT max is quite crucial.…”

Large mass field fluctuation and lattice anharmonicity effects promote thermoelectric and mechanical performances in NbFeSb half-Heusler alloys via Ti/Zr/Hf stepwise doping

“…[1][2][3] The conversion efficiency (h) strongly depends on TE materials' dimensionless gure of merit, zT = S 2 sT/(k ele + k lat ), where S is the Seebeck coefficient, s is the electrical conductivity, T is the working temperature, and k ele and k lat are the electron and lattice contributions to the total thermal conductivity (k tot ). [4][5][6][7] Over the past two decades, through theoretical and technological innovations, substantial efforts have been devoted to obtaining superior zT values. Practical strategies, such as band convergence, modulation doping, and the energy ltering effect, have been developed for optimization of the electronic properties, while defect engineering, nanostructuring, and hierarchical architectures have been applied for modulation of the thermal properties.…”