新金刚石稳定性及晶体结构模型的研究

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.

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

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.