The discovery of silicon-rich compounds with tailored electronic and thermal properties remains an important objective in materials chemistry. Here, we report the high-pressure/high-temperature (HP–HT) synthesis and theoretical characterization of a new sodium silicide, Na 2 Si 3, stabilized near 5 GPa. Na 2 Si 3 is recoverable to 1 bar. Evolutionary crystal structure prediction combined with in situ synchrotron X-ray diffraction and density functional theory calculations shows that Na 2 Si 3 adopts a tetragonal structure (space group P -42 1 m, Z = 2 ) composed of layered silicon slabs separated by sodium atoms. The bonding can be rationalized within the Zintl–Klemm framework with a formal charge distribution (Na + ) 2 (Si 0 )(Si – ) 2 . Thermodynamic calculations indicate that Na 2 Si 3 becomes stable at ∼5 GPa while remaining metastable at ambient pressure. Electronic structure calculations predict semiconducting behavior with an indirect band gap of ∼1.14 eV that increases under compression. The pentagonal topology of the silicon layers and the relatively low predicted thermal conductivity suggest potential interest for thermoelectric material design.
Redington et al. (Mon,) studied this question.