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, ρ, decreases nearly linearly with increase in compaction pressure but without a change in its slope, dρ/dT. ρ is anomalously large, and is strongly temperature and grain-size dependent. The resistivity at room temperature, ρ(300 K), is in the range ∼40-759 µΩ cm but with a positive coefficient of resistivity α (metallic). This is associated with the significantly enhanced dρ/dT with increase in residual resistivity ρ(0). These characteristics are attributed to the disorder in the grain boundaries that represents effectively a series resistor network.