The role of carbon in the formation of $\alpha$ boron at high pressure and high temperature (HPHT) has been investigated by combining HPHT experiments and density functional theory (DFT) calculations. Starting from $\beta$ rhombohedral or amorphous boron and amorphous carbon at 5 GPa, the $\alpha$ boron phase has been repeatedly observed between 1373 K and 2273 K, at temperatures that are much higher than those reported in the phase diagram of boron. The DFT investigation of the effect of carbon insertion into the $\alpha$ rhombohedral boron atomic structure on the formation enthalpy, volume and optical properties shows that the (B₁₁C) substituted icosahedron defect accounts for the slight volume contraction observed in $\alpha$ boron, is compatible with the observed red colour of $\alpha$ boron crystals, and consistently has a very low formation energy. Our calculations turn out to provide a calibration means to evaluate the concentration of carbon in our samples. Finally, the synthesis temperature is found to be an easy means to control the carbon concentration on demand.

碳在形成中的作用$\alpha$ 通过结合 HPHT 实验和密度泛函理论 (DFT) 计算研究了高压和高温 (HPHT) 下的硼。从...开始$\beta$ 菱面体或无定形硼和无定形碳在 5 GPa 下，$\alpha$ 在 1373 K 和 2273 K 之间反复观察到硼相，其温度远高于硼相图中报道的温度。碳插入的影响的DFT研究$\alpha$ 菱形硼原子结构对形成焓、体积和光学性质的影响表明，(B ₁₁ C) 取代的二十面体缺陷导致了观察到的轻微体积收缩$\alpha$ 硼，与观察到的红色相容$\alpha$ 硼晶体，并且始终具有非常低的形成能。我们的计算证明提供了一种校准方法来评估样品中的碳浓度。最后，发现合成温度是按需控制碳浓度的简便方法。