Thermal Evolution of Internal Strain in Doped PbTe

Abstract

Recent improvements in the efficiency of heat-toelectricity energy conversion in lead chalcogenide thermoelectrics involve reducing the thermal conductivity by incorporating large amounts of internal strain. The extent to which typical lead chalcogenide processing techniques (such as doping, ball milling, and densification) increase internal strain and dislocation density must be quantified to improve materials design. In this study, neutron powder diffraction is leveraged to evaluate the internal strain introduced by ball milling in doped and undoped powders. Doping with Na and/or Eu increases internal strain beyond ball milling alone, with the greatest increase from combining the two dopants. Strain recovery occurs in each powder above 400 K but can be suppressed by co-doping, indicating a strong dopant−dislocation interaction in this system. Therefore, high-temperature processing of PbTe powders should be avoided if high internal strain is desired. Low-temperature densification and/or rapid pressing techniques may be key to maintaining internal strain in the final pressed pellet. The diffraction peak asymmetry and correlated elastic softening measured in pressed PbTe pellets in past studies were not observed in the precursor powders measured here, suggesting that measurements of the Debye temperature on final pressed pellets are required to examine the influence of defect-induced elastic softening on thermal conductivity. This work provides key guidance for defect engineering to maximize internal strain and thermoelectric performance in PbTe thermoelectrics.

Thermostructural and Elastic Properties of PbTe and Pb0.884Cd0.116Te: A Combined Low-Temperature and High-Pressure X-ray Diffraction Study of Cd-Substitution Effects

“…[29,44] quoted in Table 6) and near 300 K (data from refs. [26,29,31,34,39,[41][42][43] quoted in Table 7), shows that the discrepancies between the present and earlier values of lattice parameter are quite small. Namely, near 0 K the discrepancy of the present a value, 6.42972(5) Å (the lattice parameter values given in this work with five decimal places refer to those obtained from fitted Equation (1) in this work and in the cited literature), with recent literature data, 6.42962 Å , is negligible (1 × 10 −4 Å ).…”

“…The basic thermostructural data have been reported as functions of temperature for various temperature ranges: References: (a) [36], (b) [37], (c) [38], (d) [31], (e) [34], (f) [29], (g) [39], (h) [41], (i) [40], (j) [42,43], (k) [44], (l) [45], (m) [46], (n) [47], (o) [48], (p) [49], (q) [50]. References: (a) [51], (b) [52], (c) [29], (d) [41], (e) [53], (f) [45], (g) [46], (h) [47], (i) [8], (j) [54], (k) [50]. Abbreviations are explained at the end of this study.…”

“…Abbreviations are explained at the end of this study. References: (a) [55], (b) [56], (c) [37], (d) [38], (e) [31], (f) [57], (g) [34], (h) [29], (i) [39], (j) [40], (k) [41], (l) [58], (m) [59], (n) [49], (o) [50]. (*)-the reported variation is for u(T).…”

“…The values of the fitted model (Equation ( 1)) for present and literature data are starred. References: (a) [31], (b) [29], (c) [34], (d) [39], (e) [41], (f) [26], (g) [42,43]. ($)-range of five high-quality results (see text for details); the average is corrected for thermal expansion of PbTe (the source values refer to T = 293 K).…”

“…At 300 K, the coefficient reaches the value of 20.7(8) MK −1 , the increase in respect to PbTe being about 6.5% at this temperature (the rise is comparable at lower temperatures). References: (a) [51], (b) [29], (c) [50,108], (d) [41]. (*)-theory.…”