新金刚石稳定性及晶体结构模型的研究

Studies on Stability and Crystal Structure Model of New-diamond from Catalyzed Carbon Black

利用碳黑催化法制备了新金刚石粉末,并通过粉末X射线衍射(XRD)对不同时效处理后的新金刚石样品进行表征.结果表明,新金刚石是一种亚稳态的相,在室温下,随着放置时间的推移其晶体结构发生变化.根据XRD分析和模拟的XRD图谱,提出了用具有分数占位的“缺陷金刚石”模型来解释新金刚石结构随时间的变化规律.在该模型中,原子的占位数χ为0时,为面心立方结构(FCC),χ为1时,为金刚石结构.密度泛函理论计算结果表明,随χ的增加,其结构的稳定性也增加.可见,新金刚石是由FCC碳向金刚石结构过渡的中间态结构.

After the synthesis of new-diamond by using a method of catalyzed carbon black, the crystal structure of the new-diamond after various aging-treatment time was investigated by X-ray diffraction （XRD）. The XRD patterns indicate that the new-diamond was a metastable phase, and the crystal structure of the new-diamond changed with the variation of the aging-treatment time at room temperature. Based on the XRD analysis and simulated XRD pattern, a ＂defective diamond＂ model with a fractional occupation site was proposed to explain the time-dependent the variation of the new-diamond crystal structure. In this model, the zero occupancy corresponds to a face-central cubic （FCC） crystal, while full occupation leads to a perfect diamond. A density functional theory computation further confirms the trend of increasing the stability during the evolution from FCC to diamond structure within our model. Therefore, we suggest that n-diamond is indeed an intermediate state between the FCC structure and diamond structure.