BORON AND BORON-RICH SOLIDS AT HIGH PRESSURES

摘要

Boron seems to be the indispensable ingredient to obtain materials with high hardness. It exists under many different structures. The simplest member of the family, a-boron is based on an arrangement of slightly distorted B_(12) icosahedra in a rhombohedral unit cell. B_(12)X_2 compounds, with X = O, P, As, are based on the a-boron structure, with the X atoms in the inter-icosahedra space. The stability of a-boron has been studied by x-ray diffraction and Raman scattering up to 100 GPa, showing no sign of phase transformation, and by Raman scattering for B_(12)P_2 and B_(12)As_2 with the observation of phase transformation in the 80 GPa range.