Enhancement of electrical conductivity in aluminum single crystals by boron treatment in solid state

Electrical conductivity/resistivity of elemental fcc metals, such as Al and Cu, has been investigated intensively for decades, both theoretically and experimentally. Since these metals are of great practical importance for electrical wiring, reducing their resistivity even by a few percent may have very strong impact on their application effectiveness. In this paper, we report on electrical resistivity measurements in Al single crystals grown by the Bridgman method. We found that their resistivity at room temperature decreases by 11.5% upon heat treatment in a boron environment at 600 degrees C, i.e., well below the melting temperature of Al (T-m = 660 degrees C). The residual resistivity indeed reaches its lower limit dictated by electron-phonon interaction at room temperature. We explain this effect by the boron-induced formation of distorted regions at the surface of the Al crystals. These regions are 30-50 mu m in size and comprise finer grains with an average size of 5 mu m, separated by low-angle grain boundaries. Resistivity reduction is mainly due to the getter effect, i.e., the removal of the impurity atoms from the crystal bulk by the outward diffusion to the distorted surface regions.