Structure and Physical Properties of Clathrate I Systems Ba₈Pd_xSi_46-xand Ba₈Pt_xSi_46-x

Abstract

Phase relations at 900 °C, crystal chemistry, electrical and thermal transport measurements, and heat capacity data are reported for the clathrate systems: Ba 8 {Pd,Pt} x Si 46- x . For both systems a ternary clathrate phase was identified with a small homogeneity region extending at 900 °C for 2.5≤ x Pd ≤4.1 and 2.8≤ x Pt ≤4.9, respectively. Structural investigations of these clathrate phases at 300, 200 and 100 K define cubic primitive symmetry with the space group type P m 3 n consistent with clathrate type I. Studies of electronic and thermal transport groups both series of compounds close-by a semiconducting state. An sizeable charge carrier concentration in these systems, however, prevents sufficiently large thermopower values. In comparison to isostructural type I clathrates based on Ge, thermal conductivity – dominated by the lattice contribution – is larger due to the smaller mass of Si.