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Title: Correlating thermoelectric properties with microstructure in Bi 0.8 Sb 0.2 thin films

Abstract

The room temperature electronic transport properties of 100 nm-thick thermoelectric Bi 0.8Sb 0.2 films, sputter-deposited onto quartz substrates and post-annealed in an ex-situ furnace, systematically correlate with the overall microstructural quality, improving with increasing annealing temperature until close to the melting point for the alloy composition. Furthermore, the optimized films have high crystalline quality with ~99% of the grains oriented with the trigonal axis perpendicular to the substrate surface. Film resistivities and Seebeck coefficients are accurately measured by preventing deleterious surface oxide formation via a SiN capping layer and using Nd-doped Al for contacts. Our resulting values are similar to single crystals and significantly better than previous reports from films and polycrystalline bulk alloys.

Authors:
 [1];  [1];  [1]; ORCiD logo [1]
  1. Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)
Publication Date:
Research Org.:
Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)
Sponsoring Org.:
USDOE National Nuclear Security Administration (NNSA)
OSTI Identifier:
1357018
Report Number(s):
SAND2017-0986J
Journal ID: ISSN 0003-6951; 650830
Grant/Contract Number:
AC04-94AL85000
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Applied Physics Letters
Additional Journal Information:
Journal Volume: 110; Journal Issue: 14; Journal ID: ISSN 0003-6951
Publisher:
American Institute of Physics (AIP)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE

Citation Formats

Siegal, M. P., Lima-Sharma, A. L., Sharma, P. A., and Rochford, C. Correlating thermoelectric properties with microstructure in Bi 0.8 Sb 0.2 thin films. United States: N. p., 2017. Web. doi:10.1063/1.4979785.
Siegal, M. P., Lima-Sharma, A. L., Sharma, P. A., & Rochford, C. Correlating thermoelectric properties with microstructure in Bi 0.8 Sb 0.2 thin films. United States. doi:10.1063/1.4979785.
Siegal, M. P., Lima-Sharma, A. L., Sharma, P. A., and Rochford, C. Mon . "Correlating thermoelectric properties with microstructure in Bi 0.8 Sb 0.2 thin films". United States. doi:10.1063/1.4979785. https://www.osti.gov/servlets/purl/1357018.
@article{osti_1357018,
title = {Correlating thermoelectric properties with microstructure in Bi 0.8 Sb 0.2 thin films},
author = {Siegal, M. P. and Lima-Sharma, A. L. and Sharma, P. A. and Rochford, C.},
abstractNote = {The room temperature electronic transport properties of 100 nm-thick thermoelectric Bi0.8Sb0.2 films, sputter-deposited onto quartz substrates and post-annealed in an ex-situ furnace, systematically correlate with the overall microstructural quality, improving with increasing annealing temperature until close to the melting point for the alloy composition. Furthermore, the optimized films have high crystalline quality with ~99% of the grains oriented with the trigonal axis perpendicular to the substrate surface. Film resistivities and Seebeck coefficients are accurately measured by preventing deleterious surface oxide formation via a SiN capping layer and using Nd-doped Al for contacts. Our resulting values are similar to single crystals and significantly better than previous reports from films and polycrystalline bulk alloys.},
doi = {10.1063/1.4979785},
journal = {Applied Physics Letters},
number = 14,
volume = 110,
place = {United States},
year = {Mon Apr 03 00:00:00 EDT 2017},
month = {Mon Apr 03 00:00:00 EDT 2017}
}

Journal Article:
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  • Controlling alloy composition, crystalline quality, and crystal orientation is necessary to achieve high thermoelectric performance in Bi 1-xSb x thin films. These microstructural attributes are demonstrated in this letter via co-sputter deposition of Bi and Sb metals on Si/SiO 2 substrates followed by ex-situ post anneals ranging from 200 – 300 °C in forming gas with rapid cooling to achieve orientation along the trigonal axis. We show with cross-sectional transmission electron microscopy and energy-dispersive X-ray spectrometry that 50 – 95% of the Sb segregates at the surface upon exposure to air during transfer. This then forms a nanocrystalline Sb 2Omore » 3 layer upon annealing, leaving the bulk of the film primarily Bi metal which is a poor thermoelectric material. We demonstrate a SiN capping technique to eliminate Sb segregation and preserve a uniform composition throughout the thickness of the film. Given that the Bi 1-xSb x solid solution melting point depends on the Sb content, the SiN cap allows one to carefully approach but not exceed the melting point during annealing. This leads to the strong orientation along the trigonal axis and high crystalline quality desired for thermoelectric applications.« less
  • Temperature-dependent strength of Bi-Sb-Te under uniaxial compression is investigated. Bi-Sb-Te samples were produced by three methods: vertical zone-melting, hot extrusion, and spark plasma sintering (SPS). For zone-melted and extruded samples, the brittle-ductile transition occurs over a temperature range of 200-350 °C. In nanostructured samples produced via SPS, the transition is observed in a narrower temperature range of 170-200 °C. At room temperature, the strength of the nanostructured samples is higher than that of zone-melted and extruded samples, but above 300 °C, all samples decrease to roughly the same strength.
    Cited by 1
  • Temperature-dependent strength of Bi-Sb-Te under uniaxial compression is investigated. Bi-Sb-Te samples were produced by three methods: vertical zone-melting, hot extrusion, and spark plasma sintering (SPS). For zone-melted and extruded samples, the brittle-ductile transition occurs over a temperature range of 200-350 °C. In nanostructured samples produced via SPS, the transition is observed in a narrower temperature range of 170-200 °C. At room temperature, the strength of the nanostructured samples is higher than that of zone-melted and extruded samples, but above 300 °C, all samples decrease to roughly the same strength.
  • Cited by 1
  • The PIES method (Pulverized and Intermixed Elements Sintering method) has been investigated as a new preparation technique for bismuth telluride based materials, silicon germanium based materials and so on. It has a number of advantages over the melt technique, for example, low energy inventory for preparation, low cost and short processing period, a potential for reducing grain size which favors a reduction in the thermal conductivity and an enhancement in the mechanical strength, however, the precise comparison of properties in between PIES material and the best single crystal one has not been performed. The room temperature figure of merit ofmore » the best single crystal (Bi{sub 2}Te{sub 3}){sub 0.2}(Sb{sub 2}Te{sub 3}){sub 0.8} were 2.0{similar_to}2.9{times}10{sup {minus}3} K{sup {minus}1} respectively depending on the saturation temperature and the anisotropic characteristics. On the contrary, that of PIES sample with the same composition were 2.75{times}10{sup {minus}3} K{sup {minus}1}. The figure of merit value of PIES samples were near those of the best single crystal one. {copyright} {ital 1995} {ital American} {ital Institute} {ital of} {ital Physics}.« less