Structure and Failure Mechanism of the Thermoelectric CoSb₃/TiCoSb Interface

The brittle behavior and low strength of CoSb₃/TiCoSb interface are serious issues concerning the engineering applications of CoSb₃ based or CoSb₃/TiCoSb segmented thermoelectric devices. To illustrate the failure mechanism of the CoSb₃/TiCoSb interface, we apply density functional theory to investigate the interfacial behavior and examine the response during tensile deformations. We find that both CoSb₃(100)/TiCoSb(111) and CoSb₃(100)/TiCoSb(110) are energetically favorable interfacial structures. Failure of the CoSb₃/TiCoSb interface occurs in CoSb₃ since the structural stiffness of CoSb₃ is much weaker than that of TiCoSb. This failure within CoSb₃ can be explained through the softening of the Sb-Sb bond along with the cleavage of the Co-Sb bond in the interface. The failure mechanism of the CoSb₃/TiCoSb interface is similar to that of bulk CoSb₃, but the ideal tensile strength and failure strain of the CoSb₃/TiCoSb interface are much lower than those of bulk CoSb₃. This can be attributed to the weakened stiffness of the Co-Sb framework because of structural rearrangement near the interfacial region.