Anomalous electrical transport behavior in nanocrystalline nickel

We have prepared nanocrystalline Ni (n-Ni) samples of grain sizes 40-100 nm using a polyol method and investigated the electrical transport on their compacted pellets in the temperature range 3-300 K. The resistivity, rho, decreases nearly linearly with increase in compaction pressure but without a change in its slope, d rho/dT. rho is anomalously large, and is strongly temperature and grain-size dependent. The resistivity at room temperature, rho(300) K, is in the range similar to 40-759 mu Omega cm but with a positive coefficient of resistivity alpha (metallic). This is associated with the significantly enhanced d rho/dT with increase in residual resistivity rho(0). These characteristics are attributed to the disorder in the grain boundaries that represents effectively a series resistor network.