Atomistic explanation of brittle failure of thermoelectric skutterudite CoSb3

Abstract

CoSb 3 based skutterudite thermoelectric material has superior thermoelectric properties, but the low fracture toughness prevents its widespread commercial application. To determine the origin of its brittle failure, we examined the response of shear deformation in CoSb 3 along the most plausible slip system (010)/<100>, using largescale molecular dynamics simulations. We find that the brittle failure of CoSb 3 arises from the formation of shear bands due to the destruction of Sb4-rings and the slippage of Co-octahedraes. This leads to the breakage of Co-octahedraes and cavitation, resulting in the crack opening and mechanical failure.

Structure and Failure Mechanism of the Thermoelectric CoSb3/TiCoSb Interface

“…Based on our analysis, the initial crack formation of the CoSb 3 /TiCoSb interface occurs in CoSb 3 , and arises from the softening of the Sb−Sb bond followed by the cleavage of the Co−Sb bond. As described in our previous study on CoSb 3 , 19 the calculated force constant for the Sb−Sb bond is much lower than that of the Co−Sb bond, suggesting that the covalent Sb−Sb interactions are much weaker than the ionic interactions between the Co and Sb atoms. However, the ideal tensile strength and failure strain of the CoSb 3 /TiCoSb interface are much lower than those of bulk CoSb 3 .…”

Micro- and Macromechanical Properties of Thermoelectric Lead Chalcogenides

“…To determine the structure − property relation of PbTe, we studied the elastic mechanical properties to provide essential information on the structural stability, as listed in 37,38 This suggests that PbTe has a significantly lower structural stiffness than CoSb 3 and TiNiSn. In addition, we also investigated the elastic mechanical properties of PbSe and PbS, as listed in Table 1.…”

“…The ideal shear strength (3.46 GPa) of PbTe is higher than those of layered TE materials such as Mg 3 Sb 2 (1.95 GPa) and SnSe (0.59 GPa), 40,41 but it is much lower than those of 3D TE materials with 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 12 strong covalent frameworks such as CoSb 3 (7.17 GPa) and TiNiSn (10.52 GPa). 37,38 The PbTe compound shows an extremely high zT value experimentally. 3,4 However, its ideal strength is relatively low.…”

“…This suggests that alloying PbTe with PbSe or PbS may be an effective way to improve the mechanical properties of PbTe. Moreover, we also calculated the structural rigidity, as proposed in our previous study, 37 to understand quantitatively how the structure influences the ideal strength, as shown in Figure 4 …”

“…Thus, in PbTe, the (001)/<100> slip system is most likely to be activated under pressure, which is similarly found in another FCC crystal, CoSb 3 . 37 Experimentally, alloying PbX (X = Te, Se, S) inevitably leads to defects such as vacancies, dislocations and other modulations in the samples, 51 which would not be favorable for mechanical stability. Studying these effects requires cell sizes much larger than practical for DFT.…”