Crystal Growth through Field-Assisted Electrochemical Redox and Ion-Exchange Reactions: A Case Study of K_4.2Na_3.8Si₄₆ Clathrate‑I

Single crystals of the ternary clathrate-I compound K_4.2Na_3.8Si₄₆ were grown by a unique ion-exchange process employing spark plasma sintering (SPS). Single crystal structure refinements of clathrate-I K_4.2Na_3.8Si₄₆ at 100 and 300 K indicate that the 6d crystallographic site contains both Na and K. Extended Hückel tight binding calculations suggest that K_4.2Na_3.8Si₄₆ 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