Size effects in the vibrational and electronic properties of Cu-Pb nanocomposites

Abstract

Composites of Cu and Pb (immiscible in solid state) were prepared by melt spinning onto a copper disc. X-ray diffraction measurements showed the Cu-Pb composites thus obtained to consist of Pb nanoparticles of a certain size embedded in a copper matrix. The average size of the nanocrystalline Pb blocks was determined along the normals to the (111) and (200) reflecting planes, and their size distribution was measured. The vibrational, electronic, and superconducting properties of the Cu₈₅Pb₁₅ and Cu₅₀Pb₅₀ composites were derived from low-temperature heat-capacity, magnetic-susceptibility, and resistance measurements, and the contribution of Pb nanoparticles to the heat capacity was separated. The low-frequency excitation density in Pb nanocrystals was found to increase as compared to that in crystalline Pb. The observed decrease of T _c correlates with the variation of Pb nanoparticles in size, which is a consequence of the size effect in the properties of Pb nanocrystals.