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Abstract:
The challenges associated with synthesizing expanded semiconductor
frameworks with cage-like crystal structures continue to be of
interest(1,2). Filled low-density germanium and silicon framework
structures have distinct properties that address important issues in
thermoelectric phonon glass - electron crystals(3), superconductivity(4)
and the possibility of Kondo insulators(5). Interest in empty framework
structures of silicon and germanium is motivated by their predicted wide
optical bandgaps of the same magnitude as quantum dots and porous
silicon, making them and their alloys promising materials for
silicon-based optoelectronic devices(6,7). Although almost-empty
Na1-xSi136 has already been reported(8,9), the synthesis of guest-free
germanium clathrate has so far been unsuccessful. Here we report the
high-yield synthesis and characteristics of germanium with the empty
clathrate-II structure through the oxidation of Ge-9(4-) Zintl anions in
ionic liquids under ambient conditions. The approach demonstrates the
potential of ionic liquids as media for the reactions of polar
intermetallic phases.
