铝纳米晶的低温导电特性研究

Electrical resistivity of nanostructured aluminum at low temperature

采用真空热压技术将电磁感应加热-自悬浮定向流法制备的铝纳米粉末压制成块体样品.通过X射线衍射、透射电子显微镜、扫描电子显微镜及X射线能谱分析了铝纳米晶的微观结构,并用四探针法测量了不同温度下(8—300 K)样品的电阻率,研究了铝纳米晶的电阻率(ρ)随温度的变化规律.结果表明:由于晶界(非晶氧化铝)对电子的散射以及晶界声子对电子的散射效应,低温(<40 K)下,铝纳米晶的本征电阻率随温度变化关系明显不同于粗晶铝,不仅呈现出T^4变化,还表现出显著的T3变化规律.因晶界等缺陷和非晶氧化铝杂质对电子的散射,铝纳米晶残余电阻率比粗晶铝电阻率大5—6个数量级.

The nanostructured materials have been revealed to have exclusive physical and chemical properties due to their quantum-size effects, small-size effects and a large fraction of grain boundaries. Especially, the grain boundaries play an important role in the electrical resistivity of nanostructured metal. We use the four-point probe method to measure the values of electrical resistivity（ρ） of the nanostructured aluminum samples and the coarse-grained bulk aluminum samples at temperature（T） ranging from 8 K to 300 K to explore the relationship between the electrical resistivity and temperature. The aluminum nanoparticles produced by the flow-levitation method through electromagnetic induction heating are compacted into nanostructured samples in vacuum by the hot pressing and sintering technology. The microstructures of all nanostructured aluminum samples are analyzed by X-ray diffraction（XRD）, transmission electron microscope（TEM）, scanning electron microscope with the energy-dispersive spectrometer（SEM-EDS）. The densities of all nanostructured aluminum samples are measured by using the Archimedes method（the medium is absolute alcohol）.The experimental results show that the shape of aluminum nanoparticles is found to keep spherical from the SEM images and the relative density of all nanostructured aluminum samples is about 93% of the coarse-grained bulk aluminum. The XRD spectra state that the face-centered cubic（FCC） phase dominates the samples and no diffraction peak related to impurities appears in the XRD spectrum for each of all nanostructured aluminum samples. Amorphous alumina layers（about 2 nm thick） are found to surround the aluminum nanoparticles and hence connect the grains in the nanostructured aluminum as shown in the high-resolution TEM images. Owing to the scattering of grain boundaries on electrons and the phonon-electron scattering at grain boundaries, the electrical resistivity is far larger in the nanostructured aluminum than in the coarse-grained bulk aluminum and the relationship between the electrical resistivity and temperature for nanostructured aluminum shows a different feature from that for the coarse-grained bulk aluminum. Although the temperature dependent electrical resistivity（ρ（T）） is a function of T^4 at low temperatures for the coarse-grained bulk aluminum, it varies with the temperature not only according to the relation T^4, but also according to the relation T^3 for the nanostructured aluminum. The residual resistivity（ρ_0） of the nanostructured aluminum sample is about5.5 × 10^（-4）？·m, 5–6 orders magnitude larger than that of the coarse-grained bulk aluminum（2.01 × 10^（-10）？·m） due to the scattering of both the grain boundaries and amorphous alumina on electrons therein.