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.
Small-bandwidth n-type PbTe–MnTe
alloys effectively modify
the valley shape, while it also inevitably aggravates the deterioration
of carrier mobility as nonpolar phonons dominate the scattering. It
is found that a trace amount of Cu doping can alleviate the compromises
among thermoelectric parameters, thereby significantly optimizing
the electrical-transport performance near room temperature of n-type
PbTe–MnTe alloys. The single-Kane model reveals that the physical
origin of performance improvement lies in the carrier mobility enhancement
and self-optimization of carrier concentration. The Debye–Callaway
model further quantifies the contribution of copper defect scattering
to the lattice thermal conductivity. Notably, the high thermoelectric
quality factor obtained in this work rationalizes their superior properties
and reveals immense potential for achieving higher zT. Herein, an
extremely high zT of ∼0.52 at room temperature and a maximum
zTmax of ∼1.2 at 823 K are achieved in 0.3% Cu-intercalated
n-type PbTe–MnTe. The mechanism in balancing compromise elaborated
in principle contributes to an improvement of thermoelectric properties
of the n-type PbTe alloys in a broad temperature range.
The fact that the thermoelectric performance is far inferior to that of p-type PbTe has inspired many strategies to develop n-type PbTe thermoelectrics. Alloying PbS in n-type PbTe effectively changes the shape of a valley to trigger a heavier conduction band for improving the Seebeck coefficient, while the resulting small orbital overlap inevitably leads to phase separation hindering electron transport. The effect of vacancies on the solubility of sulfur in n-type PbTe is ambiguous; especially, the heterostructure due to phase separation in high-content PbS-alloyed PbTe also requires sufficient modification to optimize the electroacoustic transport. This motivates the current work on the introduction of vacancies by charge-balancing doping via Sb2Te3 and discovers striking new insight that the introduced vacancies can induce a new heterostructure of Pb2Sb2S5 and suppress the aggregation of Sb and PbS in high-solubility n-type PbTe–PbS. The modification of the band structure and optimization of the electron transport give rise to a prominent enhancement in electronic performance. Furthermore, the Debye–Callaway model validates the dramatic contribution of vacancy aggregation and heterostructures to lattice thermal conductivity. As a result, the synergistic modulation of electroacoustic characteristics achieves a significant improvement in both the maximum zT and the near-room-temperature zT. Understanding such unique findings is critical for applicability to other thermoelectric materials.
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