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*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

13 Scopus citations

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 (US)
Article number014025
JournalPhysical Review Applied
Volume9
Issue number1
DOIs
StatePublished - Jan 24 2018

ASJC Scopus subject areas

  • Physics and Astronomy(all)

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