The crystal structure of the molybdenum boride Mo 1− xB 3

Abstract

The structure of Mo 1− x B 3, with x close to 0.20, has been investigated using powder diffractometry, in conjunction with the electron microprobe and chemical analysis. The range of homogeneity of the compound is very small and does not include the stoichiometric composition. The structure is described in the hexagonal space group P6 3 mmc with the axes a = 5.2026 (2) Å and c = 6.3489 (3) Å. No significant variations in cell dimensions were observed. There are four formula units per unit cell with molybdenum at 2( b) (occupancy 60%) and 2( c) and boron at 12( i) with x = 0.333. The refinement was performed with least-squares and Fourier difference techniques. The final R value, based on intensities, was 8.8%. The structure may be described as a stacking of two-dimensional boron nets and highly defect metal layers. The molybdenum-boron distance exceeds the radius sum by 3%, while the Mo-Mo distances are 7 and 13% longer than the radius sum. There are holes in the structure, which are large enough to accommodate boron atoms. However, there is no evidence that these holes are even partially filled.