Mechanical and thermal properties of single crystals of the type-I clathrate compounds Ba₈Ga₁₆Ge₃₀ and Sr ₈Ga₁₆Ge₃₀

The mechanical and thermal properties of single crystals of the type-I clathrate compounds Ba₈Ga₁₆Ge₃₀ and Sr ₈Ga₁₆Ge₃₀ have been investigated by measuring the elastic constants, coefficients of thermal expansion (CTE), and plastic deformation behavior in compression. The values of bulk moduli extrapolated to 0 K for Ba₈Ga₁₆Ge₃₀ and Sr₈Ga ₁₆Ge₃₀ are almost identical to each other, whereas the values of Young and shear moduli for Ba₈Ga₁₆Ge ₃₀ are larger than those for Sr₈Ga₁₆Ge ₃₀. The values of polycrystalline moduli for both Ba ₈Ga₁₆Ge₃₀ and Sr₈Ga ₁₆Ge₃₀ are all considerably smaller than those for pure germanium. The values of CTE for Ba₈Ga₁₆Ge₃₀ and Sr₈Ga₁₆Ge₃₀ are virtually identical with each other, but they are considerably larger than that of pure germanium. The feasibility of these two clathrate compounds as a thermoelectric material in terms of mechanical stability under possible thermal stresses is evaluated by calculating thermal stresses that are expected to develop within these compounds when used as a thermoelectric material in thermoelectric devises.