石墨和纳米碳中缺陷和电子密度随温度的变化

测量了石墨和纳米碳在不同温度下的正电子寿命谱,研究了石墨和纳米碳中缺陷和电子密度随温度的变化.结果表明,纳米碳中缺陷的开空间和缺陷浓度分别大于和高于石墨晶体;纳米碳的平均自由电子密度低于石墨晶体.当温度从25K升至295K时,石墨和纳米碳中的平均自由电子密度随温度的升高而下降:石墨晶体中的自由电子密度随温度的升高变化较小;纳米碳的自由电子密度随温度的升高变化较大.随着温度的升高,石墨和纳米碳中的热空位数量增多,而且这些空位可迁移至微孔洞的内表面使微孔洞的开空间增大.

VARIATION OF DEFECTS AND ELECTRON DENSITY IN GRAPHITE AND NANOCRYSTALLINE CARBON WITH TEMPERATURES

Positron lifetime spectra for graphite and nanocrystalline carbon at different temperatures have been measured. The variation of defects and electron density in graphite and nanocrystalline carbon with temperatures has been studied. The results show that the concentration and open volume of defects in nanocrystalline carbon is higher/larger than that in graphite; the mean free electron density in nanocrystalline carbon is lower than that in graphite. As the temperature increases from 25K to 295K, the mean free electron density of nanocrystalline and graphite decrease: the magnitude of the decrease of the mean free electron density of nanocrystalline is higher than that of graphite. With the increase of temperature, the amount of thermal vacancies of nanocrystalline and graphite increase, furthermore, these thermal vacancies may migrate to the inner surfaces of microvoids and increase the open volume of the microvoids.