Synthesis of an orthorhombic high pressure boron phase

The densest boron phase (2.52 g cm(-3)) was produced as a result of the synthesis under pressures above 9 GPa and temperatures up to similar to 1800 degrees C. The x-ray powder diffraction pattern and the Raman spectra of the new material do not correspond to those of any known boron phases. A new high-pressure high-temperature boron phase was defined to have an orthorhombic symmetry (Pnnm (No. 58)) and 28 atoms per unit cell.