Order-Tuned Deformability of Bismuth Telluride Semiconductors: An Energy-Dissipation Strategy for Large Fracture Strain

Abstract

In addition to thermoelectric (TE) performance tuning through defect or strain engineering, progress in mechanical research is of increasing importance to wearable applications of bismuth telluride (Bi 2 Te 3 ) TE semiconductors, which are limited by poor deformability. For improving dislocation-controlled deformability, we clarify an order-tuned energy-dissipation strategy that facilitates large deformation through multilayer alternating slippage and stacking fault destabilization. Given that energy dissipation and dislocation motions are governed by van der Waals sacrificial bond (SB) behavior, molecular dynamics simulation is implemented to reveal the relation between the shear deformability and lattice order changes in Bi 2 Te 3 crystals. Using the disorder parameter (D) that is defined according to the configurational energy distribution, the results of strain rates and initial crack effects show how the proper design of the initial structure and external conditions can suppress strain localization that would cause structural failure from the lack of energy dissipation, resulting in large homogeneous deformation of Bi 2 Te 3 nanocrystals. This study uncovers the essence of the tuning mechanism in which highly deformable Bi 2 Te 3 crystals should become disordered as slowly as possible until fracture. This highlights the role of the substructure evolution of SB-defect synergy that facilitates energy dissipation and performance stability during slipping. The disorder parameter D provides a bridge between micro/local mechanics and fracture strain, hinting at the possible mechanical improvement of Bi 2 Te 3 semiconductors for designing flexible TE devices through order tuning and energy dissipation.

Strain-Induced Defect Evolution for the Construction of Porous Cu2–xSe with Enhanced Thermoelectric Performance

“…According to the phonon gas theory: k L = 1/3 C V vl , where C V , v , and l stand for the constant volume heat capacity, sound velocity, and phonon mean free path, respectively. The reduced lattice thermal conductivity could be attributed to the reduced sound velocity and enhanced phonon scattering, consistent with a previous report. , On the other hand, the ultralow lattice thermal conductivity should also be a consequence of dynamic defect evolution including Cu ionic diffusion to dissipate energy. ,− As shown in Figure d, because the reduced electrical properties were compensated for by the diminished thermal conductivity, all porous Cu 2– x Se had a higher ZT than that of the dense samples. As a result, a maximum ZT of 1.30 was achieved in the porous Cu 1.92 Se sample at 800 K, which was an improvement of 42%.…”