posted on 2020-11-17, 21:14authored byJames
M. Hodges, Yi Xia, Christos D. Malliakas, Tyler J. Slade, Chris Wolverton, Mercouri G. Kanatzidis
A series of mixed-anion copper chalcogenides
have been prepared
using solid-state methods including ACu4.2TeS2 (A = K, Rb, Cs), which adopt the KCu4S3 structure
type. The mixed-anion motif has an expanded sublattice, relative to
KCu4S3, that can accommodate additional Cu atoms
at its interstitial sites that are unoccupied in the parent structure.
The variable temperature transport shows that the materials are p-type
metals with carrier densities on the order of 1021 cm–3 and room-temperature electrical conductivity as high
as 4000 S cm–1. Band structures calculated using
density functional theory corroborate the experimental data and indicate
that the interstitial Cu atoms lower the carrier concentration and
increase the Fermi level of the materials. The layered structure has
Te and S atoms occupying unique sites within the ACu4.2TeS2 structure, where relatively hard S2‑ anions prefer Wyckoff positions where they can form energetically
favorable acid–base interactions with hard alkali cations.
The phenomenon is observed in the related K3Cu8Te2S4 system, which also has a fully ordered
layered structure. We believe that the report provides new chemical
guidelines for targeting ordered multianion structures, as well as
a unique method for tuning the electronic properties of metallic chalcogenides.