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The low-temperature resistance and its density effects of bulk nanostructured silver

The low-temperature DC resistance and its density effects of nanostructured Ag (n-Ag) was investigated at temperatures in the range 4.2-300 K. The results indicated that the resistivity of n-Ag (size about 20 nm) exhibited metallic behaviour in the density range 88-99% similar to that of polycrystalline Ag (p-Ag). However, the absolute magnitude of the resistivity was much higher than that of p-Ag and increased with decreasing density. The specimen density not only affected the absolute value of the resistivity but also influenced the temperature coefficient of resistivity (TCR). Experiment illustrated that, with decreasing density, the TCR decreased monotonically, especially for the TCR at low temperatures (30-60 K). In addition, the position of the maximum TCR of n-Ag was higher than that of p-Ag and shifted further to higher temperatures with decreasing density. The high resistivity of n-Ag can be ascribed both to an extrinsic (macro-porosity) effect and to additional grain boundary scattering; whereas the TCR of n-Ag being lower as well as its decrease with decreasing density could be reasonably attributed to enhancement of electron scattering at grain boundaries and can be interpreted well in terms of an interfacial reflection model. The shift of the maximum TCR position to high temperature would be a reflection of the enhancement of atomic coupling within nano-grains, which will be further enhanced by de-coupling of grain boundaries.