Title: Lattice hardening due to vacancy diffusion in (GeTe)_mSb₂Te₃ alloys

Abstract

GeTe-Sb ${}_2$Te ${}_3$ alloys have been widely studied for use in rewritable media, and in recent years, they have emerged as excellent thermoelectric materials, with reports of $zT>2$ for Ge-rich compositions. GeTe-Sb ${}_2$Te ${}_3$ alloys exhibit a solid-state phase transition from a layered structure with rhombohedral symmetry to a cubic rocksalt structure, which plays an important role in their thermoelectric behavior. In this work, we investigate the impact of the phase transition on the thermal expansion and elastic moduli of (GeTe) ${}_{17}$Sb ${}_2$Te ${}_3$ using high-temperature X-ray diffraction and resonant ultrasound spectroscopy. The high-temperature elastic moduli of GeTe, Sb₂Te₃, and Bi ${}_2$Te ${}_3$ were also measured for comparison. Although it is typical for materials to soften with increasing temperature due to thermal expansion, our study reveals anomalous hardening of the elastic moduli in (GeTe) ${}_{17}$Sb ${}_2$Te ${}_3$ at temperatures below the phase transition, followed by further hardening at the transition temperature. In contrast, the elastic moduli of GeTe, Sb ${}_2$Te ${}_3$, and Bi ${}_2$Te ${}_3$ soften with increasing temperature. We attribute the anomalous hardening of (GeTe) ${}_{17}$Sb ${}_2$Te ${}_3$ to the gradual vacancy diffusion accompanying the transition from a layered to a cubic structure. The stiffening elastic moduli lead to increasing speed of sound, which impacts the lattice thermal conductivity by flattening the temperature dependence.

Authors:

Peng, Wanyue ^[1]; Smiadak, David M. ^[1]; Boehlert, Michael G.  ^[1];

• Search DOE PAGES for author "Boehlert, Michael G."
• Search DOE PAGES for ORCID "0000-0002-9792-2196"

Mather, Spencer  ^[1];

• Search DOE PAGES for author "Mather, Spencer"
• Search DOE PAGES for ORCID "0000-0002-0431-8193"

Williams, Jared B. ^[1]; Morelli, Donald T. ^[1]; Zevalkink, Alexandra ^[1]

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+ Show Author Affiliations

1. Michigan State Univ., East Lansing, MI (United States)

Publication Date:

Thu Aug 01 00:00:00 EDT 2019

Research Org.:

Michigan State Univ., East Lansing, MI (United States)

Sponsoring Org.:

USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22). Materials Sciences & Engineering Division

OSTI Identifier:

1596864

Alternate Identifier(s):

OSTI ID: 1545964

Grant/Contract Number:  

SC0019252; SC0001054

Resource Type:

Accepted Manuscript

Journal Name:

Journal of Applied Physics

Additional Journal Information:

Journal Volume: 126; Journal Issue: 5; Journal ID: ISSN 0021-8979

Publisher:

American Institute of Physics (AIP)

Country of Publication:

United States

Language:

English

Subject:

36 MATERIALS SCIENCE; 37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY