Synthesis and Structural Characterization of Single-Crystal K7.5Si46 and K17.8Si136 Clathrates

• Published in: Crystal growth & design Vol. 11; no. 10; pp. 4533 - 4537
• Main Authors: Stefanoski, Stevce, Nolas, George S
• Format: Journal Article
• Language: English
• Published: Washington,DC American Chemical Society 05-10-2011
• Subjects: Alloys; Condensed matter: structure, mechanical and thermal properties; Exact sciences and technology; Physics; Structure of solids and liquids; crystallography; Structure of specific crystalline solids; Crystal growth; Cubic lattices; Monocrystals; Silicon alloys; Selective growth; Interatomic distances; Bond angle; XRD; Potassium alloys; Clathrates; Crystal structure
• ISSN: 1528-7483; 1528-7505
• DOI: 10.1021/cg200756r

Selective single-crystal growth of clathrate-I K7.5Si46 and clathrate-II K17.8Si136 was achieved from the precursor K4Si4 by reaction of the vapor phase with spatially separated graphite in a closed volume under pressure. K7.5Si46 was prepared at a temperature of 550 °C, and K17.8Si136 was prepared at 625 °C. Structural properties of both compositions were investigated using single-crystal X-ray diffraction. We compare the structural features of K7.5Si46 and K17.8Si136 with that of Na8Si46 and Na24Si136. A Na14.7Si136 single-crystal was also synthesized and used for comparison with K17.8Si136. K@Si28 was best refined in the center of the Si28 polyhedron for K17.8Si136, in contrast to the off-center refinement of Na@Si28 for Na x Si136.