The impact of boron atoms on clathrate-I silicides: composition range of the borosilicide KBSi.

The clathrate-I borosilicide KBSi (0.8 ≤x≤ 1.2 and 6.4 ≤y≤ 7.2; space group Pm3[combining macron]n) was prepared in sealed tantalum ampoules between 900 °C and 1000 °C. By high-pressure preparation at 8 GPa and 1000 °C, a higher boron content is achieved (x = 0.2, y = 7.8). Crystal structure and composition were established from X-ray diffraction data, chemical analysis, WDX spectroscopy, and confirmed by B and Si NMR, and magnetic susceptibility measurements. The compositions are electron-balanced according to the Zintl rule within one estimated standard deviation. The lattice parameter varies with composition from a = 9.905 Å for KBSi to a = 9.968(1) Å for KBSi.