Simple Approach for Selective Crystal Growth of Intermetallic Clathrates

摘要

We report on a new method for the synthesis of single-crystal intermetallic clathrates. Alkali-metal is slowly removed from an alkali-silicide precursor by reaction of the vapor phase with spatially separated graphite, in a closed volume under uniaxial pressure, to form single-crystals of the binary intermetallic clathrates Na_8Si_(46) and Na_(24)Si_(136). Single-crystal structure refinement for Na_8Si_(46) is reported for the first time. For both Na_8Si_(46) and Na_(24)Si_(136), full occupation of all Si framework sites as well as full Na occupancy in both polyhedra was observed. In addition to comprising a simple method for selective, phase-pure crystal growth of clathrates such as Na_8Si_(46) or Na_(24)Si_(136) which was previously challenging to achieve, this or similar approaches are applicable in the preparation of new compositions from different alkali-metal precursors.