Crystal Growth through Field-Assisted Electrochemical Redox and Ion-Exchange Reactions: A Case Study of K4.2Na3.8Si46 Clathrate‑I

Single crystals of the ternary clathrate-I compound K4.2Na3.8Si46 were grown by a unique ion-exchange process employing spark plasma sintering (SPS). Single crystal structure refinements of clathrate-I K4.2Na3.8Si46 at 100 and 300 K indicate that the 6d crystallographic site contains both Na and K. Extended Hückel tight binding calculations suggest that K4.2Na3.8Si46 is metallic and that the Fermi level lies within bands having Si–Si antibonding character. The selective synthesis of clathrate-I and -II compositions was possible by changing the reaction temperature. Our results indicate that SPS can be employed in electrochemical redox and ion-exchange reactions simultaneously, thus allowing for the rapid synthesis of single crystals of multinary inorganic clathrate phases that cannot be accessible by traditional crystal growth techniques.