Deciphering the Polymorphism of CaSi: The Influence of Heat and Composition.

The Zintl phase CaSi is a layered compound with stacking variants known as 1P, 3R, and 6R. We extend the series by the 21R polytype formed by rapid cooling of the melt. The crystal structure of 21R-CaSi (space group 3̅) was derived from HRTEM images, and the atomic positions were optimized by using the FPLO code ( = 3.

A Borosilicide with Clathrate VIII Structure.

The high-pressure phase NaBSi (3 < < 5) is the first representative of a borosilicide crystallizing in the rarely occurring clathrate VIII type structure. Crystals with composition NaBSi (space group 43̅; = 9.7187(2) Å; Pearson symbol 54) were obtained at 5-8 GPa and 1200 K.