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

Abstract

The clathrate-I borosilicide K8−xBySi46−y(0.8 ≤x≤ 1.2 and 6.4 ≤y≤ 7.2; space groupPm3̄n) 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 by11B and29Si 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 froma= 9.905 Å for K7.85(2)B7.8(1)Si38.2(1)toa= 9.968(1) Å for K6.80(2)B6.4(5)Si39.6(5)