2018-5-1 · The high pressure synthesis of Na 8Alx Si 46-x was also examined, using a belt-type apparatus and employing a mixture of NaSi, Al, and Si as the reagents. In this manner, the type-I Si clathrate Na 8.7(9)Al0.5(1) Si 45(2), having a lattice parameter of 10.211(1) Ã, was synthesized at 5.5 GPa and 1570 K.