Fabrication of β-boron by chemical-reaction and melt-quenching methods at high pressures

The dependence of boron crystallization upon melt cooling has been investigated, as well as boron formation as a result of the chemical reaction of boron oxide with magnesium at a pressure of 7.7 GPa. Crystallization from the melt and the chemical reaction produce a rhombohedral β-boron phase, which is evidence of this phase stability at all temperatures up to the melting curve within the pressure range up to7.7 GPa. The melting temperatureT_mat 7.7 GPa is 2480 ± 50 K, which points to a slight positive slope of the melting curve equal to approximately 10 K/GPa. Well-shaped single crystals of boron are formed as a result of the chemical reaction and the subsequent cooling from the melt at a rate of approximately 1 K/s, indicating low viscosity of the liquid phase.