Polycrystalline ZrTe5 Parametrized as a Narrow-Band-Gap Semiconductor for Thermoelectric Performance

Samuel A. Miller, Ian Witting, Umut Aydemir, Lintao Peng, Alexander J.E. Rettie, Prashun Gorai, Duck Young Chung, Mercouri G Kanatzidis, Matthew Grayson, Vladan Stevanović, Eric S. Toberer, G. Jeffrey Snyder

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Abstract

The transition-metal pentatellurides HfTe5 and ZrTe5 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 ZrTe5 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 between 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.

Original languageEnglish
Article number014025
JournalPhysical Review Applied
Volume9
Issue number1
DOIs
Publication statusPublished - Jan 24 2018

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ASJC Scopus subject areas

  • Physics and Astronomy(all)

Cite this

Miller, S. A., Witting, I., Aydemir, U., Peng, L., Rettie, A. J. E., Gorai, P., ... Snyder, G. J. (2018). Polycrystalline ZrTe5 Parametrized as a Narrow-Band-Gap Semiconductor for Thermoelectric Performance. Physical Review Applied, 9(1), [014025]. https://doi.org/10.1103/PhysRevApplied.9.014025