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High-pressure synthesis of crystalline boron in B–H system



An experimental PT-phase diagram was proposed for boron produced by pyrolysis of decaborane B10H14 in the temperature range 1000–2100 K and pressure range 2–8 GPa. It was found that decaborane decomposes at temperatures above 1100–1400 K with a formation of either β-rhombohedral boron at pressures of 2–3 GPa or α-tetragonal boron at higher pressures. The electrical resistivity of α-tetragonal boron was measured as a function of temperature under pressures up to 5 GPa and in the temperature range 300–600 K. The energy gap between the valence and the conduction bands of α-tetragonal boron was found to be 1.52 eV. The gap decreases slightly under pressure.