Tailoring the chemical bonding of GeTe-based alloys by MgB2 alloying to simultaneously enhance their mechanical and thermoelectric performance

As a promising mid-temperature thermoelectric material, GeTe-based alloys have been intensively studied recently. Besides high figure of merit (ZT), good service stability is also significant for the practical applications of thermoelectric materials, which is especially a challenge for GeTe-based alloys having phase-transition behaviors. In this work, we have demonstrated a MgB2-alloying strategy to simultaneously enhance the mechanical and thermoelectric performance of GeTe-based alloys, owing to the tuning of chemical bonding. The negative coefficient of thermal expansion (CTE) of GeTe near the phase-transition temperature can be fully eliminated through co-alloying of Sb and MgB2. The enhancement of compressive strength and hardness by MgB2 alloying can be mainly ascribed to the solid-solution effect and the tuning of grain structures. Moreover, the Mg-substitution induced delocalization of electrons and modulation of band structures can facilitate the transport of charge carriers. Combining these MgB2-alloying effects, we can obtain (Ge0.9Sb0.1Te)(1-x)(MgB2)(x) samples with a peak ZT of 1.92 at 773 K and average ZT of 1.1 within 300-773 K, smooth CTE in the whole working temperatures, high compressive strength of similar to 271 MPa and Vickers hardness of similar to 236 H-v. The chemical-bonding mechanism developed in this work should also be potential for enhancing the overall performance of other thermoelectric materials. (C) 2020 Elsevier Ltd. All rights reserved.

Automated summary

In this study, a MgB2 alloying strategy was employed to enhance the mechanical and thermoelectric performance of GeTe-based alloys, while eliminating negative coefficient of thermal expansion (CTE) and enhancing compressive strength and hardness. The Mg-substitution induced delocalization of electrons and modulation of band structures were found to facilitate the transport of charge carriers, leading to improved ZT values of the samples.