【摘要】 采用真空热压烧结技术将平均晶粒尺寸约为52 nm的纳米铝粉末压制成铝纳米晶体材料。利用透射电镜、X射线能谱、X射线衍射、扫描电镜与综合物性测试仪(PPMS)等分析测试手段,表征了纳米铝粉和铝纳米晶体的结构特征,并研究了低温下铝纳米晶体的比热容(Cnano)随温度(T)的变化关系。研究结果表明:由于表面、晶界等缺陷的影响,铝纳米晶体的低温比热容随温度呈现出明显不同于粗晶的变化规律,其变化关系已不完全遵守德拜T3定律,且呈现出T2.5规律变化。根据纳米晶表面/界面和内部原子对晶格比热容的不同贡献,发现纳米晶相对于粗晶铝的比热容增量在温度80 K左右出现一个峰值。基于铝纳米晶体材料的结构特征和振动模式,本文探讨了产生这些现象的物理机理。更多还原

【Abstract】 Aluminum nanoparticles with an average diameter of about 52 nm were compressed to form aluminum nanocrystalline in vacuum by the hot press sintering technology. The structure of aluminum nanoparticles and nanocrystals were characterized by TEM,EDS,XRD and SEM. The physics-propertymeasurement system( PPMS) was used to measure the specific heat of aluminum nanocrystalline as a function of temperature at the low temperature. The experimental results indicate that the specific heat capacity of aluminum nanocrystalline was strikingly enhanced in compare of the bulk at the low temperatures. Due to the influence of surface,grain boundary,etc.,the low-temperature specific heat capacity of aluminum nanocrystalline changes with temperature following a relationship of T2. 5power. This is quite different from the case of coarse grain aluminum,which follows T3power( Debye’s law). The experimental data are in good agreement with a model which considers contributions from the surface and core atoms in the nanoparticles. The excess specific heat is deduced as a low temperature peak at 80 K. The physical mechanism for the phenomenon was discussed on the basis of the structure characteristics and vibration modes of aluminum nanocrystalline.更多还原