RESUMO
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- x Nax Te 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 Pb0.95 Na0.04 Te sample, reaching maximum zTmax ≈ 2.0 at 823 K, which achieves an ultra-high performance in only Na-doped ternary Pb1- x Nax Te 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.
RESUMO
Bi2Te3 is a well-recognized material for its unique properties in diverse thermoelectric applications near room temperature. The considerable efforts on Bi2Te3-based alloys have been extremely extensive in recent years, and thus the latest breakthroughs in high-performance p-type (Bi, Sb)2Te3 alloys are comprehensively reviewed to further implement applications. Effective strategies to further improve the thermoelectric performance are summarized from the perspective of enhancing the power factor and minimizing the lattice thermal conductivity. Furthermore, the surface states of topological insulators are investigated to provide a possibility of advancing (Bi, Sb)2Te3 thermoelectrics. Finally, future challenges and outlooks are overviewed. This review will provide potential guidance toward designing and developing high-efficient Bi2Te3-based and other thermoelectrics.
RESUMO
p-Type (Bi, Sb)2Te3 alloys are attractive materials for near-room-temperature thermoelectric applications due to their high atomic masses and large spin-orbit interactions. However, their narrow band gaps originating from spin-orbit interactions lead to bipolar excitation, thereby limiting average thermoelectrics within a local temperature region (300-400 K). Here, we introduce Cu2Te into the Bi0.3Sb1.7Te3 (BST) lattice to implement high thermoelectrics over a wide temperature range. The carrier concentration is synergistically modulated via Cu substitution and the evolution of intrinsic point defects (antisites and vacancies). Furthermore, the chain effect caused by Cu2Te incorporation in BST is reflected in the improvement of the weighted mobility µW, thereby enhancing the power factor in the whole temperature range. Extrinsic and intrinsic defects due to the incorporation of Cu2Te lead to a significant reduction in the lattice thermal conductivity κL, which is further demonstrated by Raman spectroscopy. Combining κL and µW, the quantity factor B increases from 0.5 to 1 with increasing Cu2Te content due to not only the reduction of κL but also a significant improvement in electrical properties. Eventually, a peak figure of merit (zT) of â¼1.15 at 423 K is achieved in BST-Cu2Te samples, and an average figure of merit (zTave) of â¼1.12 (350-500 K) surpasses other excellent p-type Bi2Te3-based thermoelectrics. Such a synergistic effect can facilitate near-room-temperature thermoelectric applications of Bi2Te3-based alloys and provide chances for the technology space in thermoelectrics.
