Synthesis and solid-state transformations of Cu core/Ni shell nanoparticles

Air stable Cu core/Ni shell nanoparticles have been prepared in a two step polyol-type process by adding CuCl$_{2}\cdot $2H$_{2}$O and NaOH to an ethylene glycol solution at 160 \r{ }C followed by the subsequent addition of NiCl$_{2}\cdot $6H$_{2}$O and NaOH at a solution temperature of 180 \r{ }C. Allowing the low temperature step of the reaction to proceed to completion ensured that the high temperature step resulted in the formation of elemental Ni rather than a Cu-Ni alloy as verified from the near bulk values of the measured Cu and Ni lattice parameters. The solid-state transformation from the as-prepared core/shell structure to an essentially homogeneous Cu-Ni alloy has been studied by differential scanning calorimetry, x-ray diffraction, and vibrating sample magnetometry measurements. These measurements reveal that the core/shell structure remains largely intact to temperatures above 400 \r{ }C during an annealing profile consisting of a 20 \r{ }C/min temperature ramp followed by a rapid temperature quench.