Mechanical and thermal properties of single crystals of the type-I clathrate compounds Ba8Ga16Ge30 and Sr8Ga16Ge30

The mechanical and thermal properties of single crystals of the type-I clathrate compounds Ba(8)Ga(16)Ge(30) and Sr(8)Ga(16)Ge(30) 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 Ba(8)Ga(16)Ge(30) and Sr(8)Ga(16)Ge(30) are almost identical to each other, whereas the values of Young and shear moduli for Ba(8)Ga(16)Ge(30) are larger than those for Sr(8)Ga(16)Ge(30). The values of polycrystalline moduli for both Ba(8)Ga(16)Ge(30) and Sr(8)Ga(16)Ge(30) are all considerably smaller than those for pure germanium. The values of CTE for Ba(8)Ga(16)Ge(30) and Sr(8)Ga(16)Ge(30) 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. (c) 2008 American Institute of Physics.