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

Synthesis, crystal structure and physical properties of the clathrate-I phase Ba8RhxSi46−x−y□y

“…This resulted in compositions close to Ba 8 Rh 2.4 Si 43.6 . However, WDXS measurements performed on seven samples with nominal compositions in the range Ba 8 Rh 6 Si 40 to Ba 8 Rh 3 Si 43 showed a significantly higher rhodium content of the clathrate phase with a mean composition Ba 8 Rh 2.74(2) Si 42.15 (12) .…”

Synthesis and Structural Characterization of the New Clathrates K8Cd4Ge42, Rb8Cd4Ge42, and Cs8Cd4Ge42

“…The small deviations in the refined Cd content must also have an effect on the unit cell volumes, but it is expected to be subtle (the difference in the refined Cd content is less than 2σ). Notice, however, that in the single-bonded Pauling radii for the Cd and Ge are quite different, r Ge ≈ 1.24 Å, r Cd ≈ 1.38 Å [26], and, as a result, the Cd substitutions to the Ge-based framework result in enlargement of the unit cell, clearly seen by comparing our data with the data for the known binary type-I clathrates K 8 Ge 44 ☐ 2 [27] and Cs 8 Ge 44 ☐ 2 [28], which have periodicity constants of a = 10.686(4) Å and a = 10.8238(2) Å, respectively. Of course, the presence of vacancies in the framework for K 8 Ge 44 ☐ 2 and Cs 8 Ge 44 ☐ 2 (☐ = vacancy) should not be overlooked, as it contributes to the contraction of the unit cell.…”

Preparation and Crystal Structure of the Clathrate‐I Cs8–xGe44+y□2–y

“…For a type‐I clathrate with general composition Cs 8– x E 46– y , eight E 2 atoms have the shortest distance to Cs1 at the center of the E 20 dodecahedra (Figure 5a), whereas eight E 3 atoms have the shortest distance to Cs2 at the center of the E 24 tetrakaidecahedra (Figure 5b). The actual distance d (Cs2– E 3) depends on the presence of defects at E 1 in the E 24 cage, because the E 3 positions are found to be shifted in presence of a neighboring defect 20,25. As a consequence, the free volume for a spherical atom inside an E 24 polyhedron is smaller , when the cage contains a defect at an E 1 position (Table 5).…”

“…Differently to the metallic silicides, the clathrate germanide ‘K 8 Ge 46 ’ showed semiconductor‐like transport behavior 16. This apparent inconsistency of experimental facts was solved at one stroke by an extended structure model of Hans Georg von Schnering 17–20. A crystal structure redetermination of ‘K 8 Ge 46 ’ revealed its actual composition K 8 Ge 44 □ 2 and the evidence that two vacancies □ occur in the germanium framework per formula unit.…”