posted on 2022-02-01, 18:05authored byJacob McKenzie, Khoa N. Le, Dylan J. Bardgett, Kelsey A. Collins, Thomas Ericson, Michael K. Wojnar, Julie Chouinard, Stephen Golledge, Anthony F. Cozzolino, David C. Johnson, Christopher H. Hendon, Carl K. Brozek
“Open-framework chalcogenides”
are an important class
of materials that combine porosity with semiconductor behavior, and
yet fundamental aspects of their conductivity remain unexplored. Here,
we report a combined experimental–computational approach to
the iconic subclass of materials TMA2MGe4Q10 (TMA = tetramethyl ammonium; M = Mn, Fe, Co, Ni, Zn; Q =
S, Se). Direct current (DC) conductivity measurements and density
functional theory (DFT) modeling reveal that metal ion and chalcogenide
identities dominate key properties of the band structures, while impedance
spectroscopy reveals purely electronic band-type transport in the
Fe frameworks and redox-type mixed ion–electron conductivity
in the others. Redox chemistry and computation suggest that the unique
conductivity of Fe arises from its propensity toward Fe2+/Fe3+ mixed valency as a source of p-type doping and from
its highly covalent bonds that ensure high carrier mobilities. Taken
together, these results demonstrate open-framework chalcogenides as
a well-defined platform for understanding porous semiconductors and
for achieving highly tunable electronic performance.