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Title: Polycrystalline ZrTe 5 Parametrized as a Narrow-Band-Gap Semiconductor for Thermoelectric Performance

The transition-metal pentatellurides HfTe 5 and ZrTe 5 have been studied for their exotic transport properties with much debate over the transport mechanism, band gap, and cause of the resistivity behavior, including a large low-temperature resistivity peak. Single crystals grown by the chemical-vapor-transport method have shown an n-p transition of the Seebeck coefficient at the same temperature as a peak in the resistivity. We show that behavior similar to that of single crystals can be observed in iodine-doped polycrystalline samples but that undoped polycrystalline samples exhibit drastically different properties: they are p type over the entire temperature range. Additionally, the thermal conductivity for polycrystalline samples is much lower, 1.5 Wm -1 K -1, than previously reported for single crystals. It is found that the polycrystalline ZrTe 5 system can be modeled as a simple semiconductor with conduction and valence bands both contributing to transport, separated by a band gap of 20 meV. This model demonstrates to first order that a simple two-band model can explain the transition from n- to p-type behavior and the cause of the anomalous resistivity peak. Combined with the experimental data, the two-band model shows that carrier concentration variation is responsible for differences in behavior betweenmore » samples. Using the two-band model, the thermoelectric performance at different doping levels is predicted, finding zT=0.2 and 0.1 for p and n type, respectively, at 300 K, and zT=0.23 and 0.32 for p and n type at 600 K. Given the reasonably high zT that is comparable in magnitude for both n and p type, a thermoelectric device with a single compound used for both legs is feasible.« less
Authors:
 [1] ;  [1] ;  [2] ;  [1] ;  [3] ;  [4] ;  [3] ;  [5] ;  [1] ;  [4] ;  [4] ;  [1]
  1. Northwestern Univ., Evanston, IL (United States)
  2. Northwestern Univ., Evanston, IL (United States); Koc Univ., Istanbul (Turkey)
  3. Argonne National Lab. (ANL), Argonne, IL (United States)
  4. National Renewable Energy Lab. (NREL), Golden, CO (United States); Colorado School of Mines, Golden, CO (United States)
  5. Argonne National Lab. (ANL), Argonne, IL (United States); Northwestern Univ., Evanston, IL (United States)
Publication Date:
Report Number(s):
NREL/JA-5K00-71006
Journal ID: ISSN 2331-7019; PRAHB2; TRN: US1801719
Grant/Contract Number:
AC36-08GO28308; SC0001299/DE-FG02-09ER46577
Type:
Accepted Manuscript
Journal Name:
Physical Review Applied
Additional Journal Information:
Journal Volume: 9; Journal Issue: 1; Journal ID: ISSN 2331-7019
Publisher:
American Physical Society (APS)
Research Org:
National Renewable Energy Lab. (NREL), Golden, CO (United States)
Sponsoring Org:
USDOE Office of Energy Efficiency and Renewable Energy (EERE); USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; 71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; band gap; charge density waves; thermoelectric effects; semiconductor compounds
OSTI Identifier:
1423194
Alternate Identifier(s):
OSTI ID: 1417937