Enhanced Strength Through Nanotwinning in the Thermoelectric Semiconductor InSb

Abstract

The conversion efficiency (zT) of thermoelectric (TE) materials has been enhanced over the last two decades, but their engineering applications are hindered by the poor mechanical properties, especially the low strength at working conditions. Here we used density functional theory (DFT) to show a strength enhancement in the TE semiconductor InSb arising from the twin boundaries (TBs). This strengthening effect leads to an 11% enhancement of the ideal shear strength in flawless crystalline InSb where this theoretical strength is considered as an upper bound on the attainable strength for a realistic material. DFT calculations reveal that the directional covalent bond rearrangements at the TB accommodating the structural mismatch lead to the anisotropic resistance against the deformation combined with the enhanced TB rigidity. This produces a strong stress response in the nanotwinned InSb. This work provides a fundamental insight for understanding the deformation mechanism of nanotwinned TE semiconductors, which is beneficial for developing reliable TE devices.

Strengthening boron carbide through lithium dopant

“…Therefore, enhancing materials strength has been a very hot research area . Many approaches have been proposed and tested to enhance the strength of many types of materials such as metals, semiconductors, and superhard materials . The traditional method of strengthening metals is to control the precipitants and grain boundaries (GBs) so that the mobile dislocations are suppressed .…”

“…[3][4][5] Boron carbide (B 4 C), one of the hardest known materials after diamond and cubic boron nitride, 6 has potential to be widely adopted into military, aerospace and aviation, and industry applications such as antiballistic armor plating, warship coating, reactor neutron absorbent, abrasives, and so on. [3][4][5][6][7][8][9][10][11][12] The high strength of B 4 C is essential in these applications, making it important to further enhance its strength through various approaches such as introducing nanotwins [13][14][15][16][17][18][19] and making nanocomposites. 20 Furthermore, B 4 C suffers from abnormal brittle failure above the critical failure strength due to the amorphous shear band formation.…”

“…strength of many types of materials such as metals, [23][24][25] semiconductors, 14,15 and superhard materials. 13,18,20 The traditional method of strengthening metals is to control the precipitants and grain boundaries (GBs) so that the mobile dislocations are suppressed.…”

“…15,26 Considering that TBs normally have a lower interfacial energy than normal GBs, 19 it is advisable to incorporate nanoscale twins into metals and ceramics to enhance their strength. 23,[28][29][30][31][32][33][34] For example, ultrastrength phenomena have been observed in nanotwinned InSb 14 and Bi 2 Te 3 15 due to various strengthening mechanisms such as forming stronger GB bonding in Bi 2 Te 3 and suppressing the easy shear slip in InSb, respectively. In addition, it has been observed in experiments that the strength and hardness are enhanced significantly in nanotwinned cubic boron nitride 13,16 and nanotwinned diamond.…”

Carbon-Based Materials for Thermoelectrics

“…In low-strength TE materials, such as GaAs, ZnSe, Bi 2 Te 3 , and InSb, several studies focused on engineering the material microstructure to increase the mechanical strength. For example, Snyder et al introduced nanosized twin boundaries into InSb and found an 11% increase in shear strength [65]. In another work, Snyder et al found that spark plasma sintering (SPS) reduced the grain size of (Bi,Sb) 2 Te 3 compared to the samples processed with the traditional zone-melting method.…”