Rapid crystal growth of type-II clathrates A8Na16Si136 (A = K, Rb, Cs) by spark plasma sintering

Abstract

Single crystal type-II clathrates A₈Na₁₆Si₁₃₆ (A = K, Rb, and Cs) were grown from NaSi and alkali metal halides by spark plasma sintering (SPS). Single crystal structure refinements indicate that K atoms at the 8b crystallographic site are partially occupied (K_5.8(1)Na₁₆Si₁₃₆) while Rb in Rb₈Na₁₆Si₁₃₆ and Cs in Cs₈Na₁₆Si₁₃₆ are fully occupied. Our results indicate that SPS can be employed in topochemical ion exchange reactions, thus allowing for the rapid synthesis of single crystals of multinary intermetallic phases that cannot be accessible by traditional crystal growth techniques.