Deformation and Failure Mechanisms of Thermoelectric Type-I Clathrate Ba₈Au₆Ge₄₀

Type-I clathrate Ba₈Au₆Ge₄₀, possessing an interesting structure stacked by polyhedrons, is a potential "phonon-glass, electron-crystal" thermoelectric material. However, the mechanical properties of Ba₈Au₆Ge₄₀ vital for industrial applications have not been clarified. Here, we report the first density functional theory calculations of the intrinsic mechanical properties of thermoelectric clathrate Ba₈Au₆Ge₄₀. Among the different loading directions, the {110}/⟨001⟩ shearing and ⟨110⟩ tension are the weakest, with strengths of 4.51 and 6.64 GPa, respectively. Under {110}/⟨001⟩ shearing, the Ge-Ge bonds undergo significant stretching and twisting, leading to a severe distortion of the tetrakaidecahedral cage, giving rise to the fast softening of the flank Au-Ge bonds. At a strain of 0.2655, the Au-Ge bonds suddenly break, resulting in the collapse of the cage and the failure of the material. Under a ⟨110⟩ tension, the stretching of the Ge-Ge bonds keeps accelerating the softening of the Au-Ge bonds in the top/bottom hexagons, which releases the stress and disables the structure. The Au-Ge bonds are more rigid, contributing two-thirds of the structural deformation resistance. This work provides a new insight to understand the failure mechanisms of type-I clathrates with varied framework constitutions, which should help inform the design of robust thermoelectric clathrate materials.