The impact of boron atoms on clathrate-I silicides: composition range of the borosilicide K8−xBySi46−y

Abstract

The clathrate-I borosilicide K_8−xB_ySi_46−y (0.8 ≤ x ≤ 1.2 and 6.4 ≤ y ≤ 7.2; space group Pmn) 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 ¹¹B and ²⁹Si 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 K_7.85(2)B_7.8(1)Si_38.2(1) to a = 9.968(1) Å for K_6.80(2)B_6.4(5)Si_39.6(5).