Defects responsible for abnormal n-type conductivity in Ag-excess doped PbTe thermoelectrics

Abstract

We find that Ag-interstitial (Ag I ) acts as an electron donor and plays an important role in Ag-excess doped polycrystalline PbTe thermoelectric materials. When Ag is heavily doped in PbTe, the neutral (Ag-Ag) dimer defect is formed at the Pb-site and the environment becomes Pb-rich/Te-poor condition. Then the positively ionized Ag interstitial (Ag I + ) defect becomes the major defect under Pb-rich condition. Due to the small formation energy and small diffusion barrier of Ag I + , Ag can be easily dissolved into the PbTe matrix.The temperature behavior of the Ag defect formation energy well explains the Ag I + solubility, the electron carrier generation, and the increasing electrical conductivity in Ag-excess doped polycrystalline PbTe at high temperature. This abnormal doping behavior by forming interstitial defects is also found for Au-doped PbTe.

On the relevance of point defects for the selection of contacting electrodes: Ag as an example for Mg2(Si,Sn)-based thermoelectric generators

“…Using the method of climbed nudged elastic band (cNEB) calculations [59,66,67], we reveal that Ag defects in Mg2Si can easily diffuse to form AgMg defects via the interstitial diffusion of the IAg interstitial defect with a migration energy barrier of 0.652 eV. When the Fermi level is 0 (i.e.…”

“…where Etot [D q ] and E0 are the total energies with and without defect in the supercell, j is the atomic species in the supercell, Δnj is the number change of atomic species j in the defective supercell with respect to the pristine supercell without defects, EF is the electron Fermi level, and ECBM is the energy of the conduction band minimum (CBM) [43,58,59]. Note that for the defects, the total energies were calculated using HSE06.…”

Enhancing Thermoelectric Performances of Bismuth Antimony Telluride via Synergistic Combination of Multiscale Structuring and Band Alignment by FeTe2 Incorporation

“…The electronic structures are calculated for an optimized structure with an inclusion of spin–orbit interaction, which is found to be very important to describe the band structure and the formation energy of defects for heavy-element-containing materials . The formation energy E form of the defect is calculated by using the formalism in the literature. − It is noted that there is a difficulty in predicting the band structure of Bi 2 Te 3 and the shallow defects with hybrid functionals. , …”

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

“…On the other hand, high-resolution Te 3d orbits (Figure d) display smaller peaks corresponding to Na–Te bonds (∼583.2 eV) in Pb 0.93 Na 0.04 Mn 0.02 Te compared to the matrix, further confirming an improved solubility of Na. Moreover, it should be noted that the strong intensity of Te–O bonds and Pb–O bonds (Figure S4b) can be attributed to the inevitable air exposure during the performance testing and characterization, which is commonly observed in PbTe-based 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.…”