The impact of boron atoms on clathrate-I silicides: composition range of the borosilicide K_8−xB_ySi_46−y

Abstract

The clathrate-I borosilicide K8−xBySi46−y (0.8 ≤ x ≤ 1.2 and 6.4 ≤ y ≤ 7.2; space group Pm3̄n) was prepared in sealed tantalum ampoules between 900 °C and 1000 °C.

Temperature-dependent crystal structure investigation of 4f hybridized thermoelectric clathrate Ba8–x Ce x Au y Si46–y

“…Thus, the Au atoms are predominantly ordered on the 6c site, with a small degree of distribution across the 24k sublattice, in agreement with previous results in the literature for the BAS/BCAS system (Aydemir et al, 2011;Jaussaud et al, 2005;Prokofiev et al, 2013). A similar pattern is seen in boron silicon clathrates where there is a minor substitution of boron on the 24k site, although in this system it is the 16i and not the 6c site that functions as the majority substitution site (Hu ¨bner, Jung, Koz ˇelj et al, 2021; Hu ¨bner, Jung, Schmidt et al, 2021;Jung et al, 2021). The 6c site is unique to the extent that it is the only host site with no direct bonds to its symmetry equivalent positions, whereas direct 24k-24k and 16i-16i bonds are present in the framework structure.…”

A Borosilicide with Clathrate VIII Structure

“…Nonetheless, the finding of a clathrate VIII was a surprise because our experiments aimed to complete the clathrate I borosilicides M 8– x B y Si 46– y ( M = K, Rb, Cs) with M = Na. In this series, only the representative K 7 B 7 Si 39 , which is remarkably stable against oxidizing environments, , was prepared at ambient pressure. The clathrate I borosilicides with large cations Rb 8 B 8 Si 38 and Cs 8 B 8 Si 38 only form under high-pressure conditions.…”

“…Depending on the synthesis pressure (5–8 GPa), the lattice parameter of clathrate VIII Na 8 B x Si 46– x varies from a = 9.7579(6) to 9.6750(4) Å. In the type I clathrate K 8– y B x Si 46– x , the substitution of Si by B causes a reduction of the lattice parameter of Δ a ≈ 0.04 Å/atom. Therefore, with a = 9.7187(2) Å for Na 8 B 4.1 Si 41.9 , a composition range of Na 8 B 3 Si 43 –Na 8 B 5 Si 41 can be estimated.…”

“…Because of mixed occupancy with B and Si, the Si2–Si2 distance represents the superposition of a Si–Si and a B–Si bond (Table ). Because of the low scattering power of the crystal, split positions for Si2 are not resolved. The refinement results in a residual value R F = 0.05 and the composition Na 8 B 4.1(7) Si 41.9(7) .…”