Transport Properties of the Binary Type I Clathrate K₈Ge₄₄□₂

Abstract

We report the synthesis and low‐temperature electrical resistivity, Seebeck coefficient, and thermal conductivity of the binary type I clathrate K8Ge44□2 (□=Ge framework vacancy). Electrical resistivity measurements indicated metallic or heavily doped semiconductor behavior, while the Seebeck was relatively high at −77 μV/K at room temperature. The thermal conductivity was very low, on the order of 1 W/m K at room temperature. This work is part of a continuing effort to investigate new compositions in open‐structured and guest‐framework materials for potential thermoelectric applications.

Refinement of the crystal structure of K8Ge44⬜2, an intermetallic clathrate I

“…» 0.3) provides another independent crystallographic proof for the defect concentration at site 6c [10] which is in particular an important tool for the refinement of ternary clathrates with heteroatomic frameworks [11]. The framework defects in K 8 Ge 44 £ 2 have been confirmed in recent works from powder diffraction data [12,13]. Moreover, the validity of the split atom model has been proven by the detection of superstructures with ordered defect arrangement (space group Ia3d )for the clathrate-I phases Rb 8Sn44£2 [14], Cs8Sn44£2 [15] and Ba 8Ge43£3 [9,16,17].…”

Formation of Vacancies in Si- and Ge-based Clathrates: Role of Electron Localization and Symmetry Breaking

“…K 8 Si 46 [4][5][6] and Ba 8 Si 46 [7][8][9]) results. In the case of Ge, vacancies occur in the host framework: In line with Zintl's concept, a heavily doped semiconductor K 8 Ge 44 2 featuring two framework vacancies was found experimentally for monovalent K guests [6,10]. For divalent Ba guests, however, experiments [14,15] found a metallic Ba 8 Ge 43 3 compound with three vacancies, but not four, as expected from the increased Ba valence.…”

Si‐based Clathrates with Partial Substitution by Zn and Ga: K8Zn3.5Si42.5, Rb7.9Zn3.6Si42.4, and Cs8–xGa8–ySi38+y

“…Formally, the interaction between host and guest atoms can be described by a charge transfer from the guest atoms to the framework atoms. For binary clathrates with a Ge and Sn framework the charge balance is achieved by the formation of defects in the framework as observed for Ba 8 Ge 43 21, K 8 Ge 44 ,22 Rb 8 Sn 44 ,23 or Cs 8 Sn 44 ,24 whereas for binary silicides no defects but metallic properties have been reported 25. For ternary clathrates with a framework formed by group 13 ( E III ) and 14 ( E IV ) elements a charge balance is achieved for the compositions A 8 E III 8 E IV 38 and AE 8 E III 16 E IV 30 according to the charges of the four‐bonded (4b) atoms 4b‐Tr – and 4b‐Tt 0 such as K 8 Ga 8 Si 38 19a and Ba 8 Al 16 Ge 30 14, respectively.…”