First principles investigation of intrinsic and Na defects in XTe (X=Ca, Sr, Ba) nanostructured PbTe

Zhang, Xuemei; Toriyama, Michael Y.; Male, James P.; Feng, Zhenzhen; Guo, Shuping; Jia, Tiantian; Ti, Zhuoyang; Snyder, G. Jeffrey; Zhang, Yongsheng

doi:10.1016/j.mtphys.2021.100415

Cited by 8 publications

(7 citation statements)

References 77 publications

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“…General trends in doping efficiency determined in both this study and others [ 41,50–53 ] find near ≈ 100 % doping efficiency up to high n H from classic n‐type dopants like I and La, while the doping efficiency of p‐type dopants drops off steeply at high n H —likely due to pervasive compensating V

_{Te}^{• •}

and Te

_{Pb}^{• •}

defects. [ 14,54–56 ] Therefore, high p‐type n H values in PbTe require higher (orders of magnitude) concentrations of both doping atoms and intrinsic defects than n‐type samples with the same absolute n H . Substitutional p‐type Ag and K are less efficient dopants than Na, and likewise have vastly higher intrinsic defect concentrations at low n H .…”

Section: Resultsmentioning

confidence: 99%

“…Compensated (Pb‐rich) Na‐doped samples have primarily V

_{Te}^{• •}

intrinsic defects, while uncompensated samples have high Te

_{Pb}^{• •}

concentrations. [ 14,54–56 ] Both defects appear to harden PbTe, but generally higher hardness in uncompensated, Na‐doped PbTe suggests that Te

_{Pb}^{• •}

does so more rapidly. The mechanism behind Te

_{Pb}^{• •}

hardening requires more rigorous examination.…”

Section: Resultsmentioning

confidence: 99%

“…Compensated (Pb-rich) Na-doped samples have primarily VTe •• intrinsic defects, while uncompensated samples have high Te Pb •• concentrations. [14,[54][55][56] Both defects appear to harden PbTe, but generally higher hardness in uncompensated, Table 1. Dopants explored in this study and their relative ionic size differences [37] to their host atoms (Δ IR ) shown along with the Vickers microhardness change observed in PbTe doped with the listed dopants relative to undoped PbTe.…”

Section: Dislocations Cause Embrittlementmentioning

confidence: 99%

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Dislocations Stabilized by Point Defects Increase Brittleness in PbTe

Male

Abdellaoui

et al. 2021

Adv Funct Materials

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Dislocations and the residual strain they produce are instrumental for the high thermoelectric figure of merit, zT ≈ 2, in lead chalcogenides. However, these materials tend to be brittle, barring them from practical green energy and deep space applications. Nonetheless, the bulk of thermoelectrics research focuses on increasing zT without considering mechanical performance. Optimized thermoelectric materials always involve high point defect concentrations for doping and solid solution alloying. Brittle materials show limited plasticity (dislocation motion), yet clear links between crystallographic defects and embrittlement are hitherto unestablished in PbTe. This study identifies connections between dislocations, point defects, and the brittleness (correlated with Vickers hardness) in single crystal and polycrystalline PbTe with various n‐ and p‐type dopants. Speed of sound measurements show a lack of electronic bond stiffening in p‐type PbTe, contrary to the previous speculation. Instead, varied routes of point defect–dislocation interaction restrict dislocation motion and drive embrittlement: dopants with low doping efficiency cause high defect concentrations, interstitial n‐type dopants (Ag and Cu) create highly strained obstacles to dislocation motion, and highly mobile dopants can distribute inhomogeneously or segregate to dislocations. These results illustrate the consequences of excessive defect engineering and the necessity to consider both mechanical and thermoelectric performance when researching thermoelectric materials for practical applications.

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_{Te}^{• •}

and Te

_{Pb}^{• •}

Section: Resultsmentioning

confidence: 99%

“…Compensated (Pb‐rich) Na‐doped samples have primarily V

_{Te}^{• •}

intrinsic defects, while uncompensated samples have high Te

_{Pb}^{• •}

concentrations. [ 14,54–56 ] Both defects appear to harden PbTe, but generally higher hardness in uncompensated, Na‐doped PbTe suggests that Te

_{Pb}^{• •}

does so more rapidly. The mechanism behind Te

_{Pb}^{• •}

hardening requires more rigorous examination.…”

Section: Resultsmentioning

confidence: 99%

Section: Dislocations Cause Embrittlementmentioning

confidence: 99%

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Dislocations Stabilized by Point Defects Increase Brittleness in PbTe

Male

Abdellaoui

et al. 2021

Adv Funct Materials

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“…Lead chalcogenide-based compounds PbM (M = Te, S, Se) and their alloys have been engineered to exhibit high zT values in the medium-temperature range (600–900 K). ,− PbTe-based alloys have some of the highest reported zT values, zT > 2 above 923 K reported by several groups. Much of its excellent thermoelectric performance can be attributed to the addition of band-converging additives: starting with isovalent additives such as Mg, Sr (Pb 0.98 Na 0.02 Te–8%SrTe system), Cd, Hg, Mn, etc.…”

Section: Introductionmentioning

confidence: 99%

Band Engineering SnTe via Trivalent Substitutions for Enhanced Thermoelectric Performance

et al. 2021

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SnTe is an attractive candidate for applications as a p-type thermoelectric semiconductor. The pristine SnTe compound exhibits poor thermoelectric performance at high temperatures because of its high hole concentration, small band gap, and large energy difference between the light and heavy bands (ΔE(L – Σ)). To overcome these problems, we investigate band structure changes upon the addition of trivalent dopants based on the tight-binding (TB) model and density functional theory (DFT) calculations. We find that tuning the relative on-site energies of the cation and anion s and p orbitals is a potential route for engineering band convergence. Codoping with Ge in addition to trivalent substitutions further enhances thermoelectric performance. We find that a low concentration of the isovalent Ge as well as As, which also acts as a donor (Sn0.952Ge0.016As0.016Te), induces band convergence (ΔE(L – Σ) = 0.12 eV) and enlarges the band gap (0.20 eV). This band convergence results in a remarkable increase of the peak power factor, while the increased band gap energy suppresses detrimental bipolar effects. We find that the theoretical and experimental results are in good agreement here, and the high power factor (high weighted mobility) can be attributed to the increased band convergence. Our work can efficiently screen the promising trivalent substitutions in SnTe-based materials codoped with Ge and find promising candidates for improved thermoelectric performance.

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“…The Pb and Te vacancies have a low defect formation energy in the PbTe twin boundary. 83 It indicates that these defects are more easily formed in the twin boundary and can optimize the thermal transport properties of PbTe. Thus, focusing on the vacancy point defects within the two kinds PbTe twin boundary, we calculate the thermal conductivity with different defect concentrations (Fig.…”

Section: Resultsmentioning

confidence: 99%