The impact of particle morphology on the melting characteristics of matrix-embedded Pb nanocrystals

摘要

The melting behaviour of Pb nanoparticles embedded in an Al matrix (0.5 at .% Pb) synthesized by high-energy ball milling is investigated. By differential scanning calorimetry it is shown that, as the material is cycled repeatedly through the melting transition, the particles melt reversibly at temperatures T_f below the melting temperature T_f~0 of bulk Pb. However, after a suitable heat treatment the nanoparticle morphology is modified such that a significant fraction of the Pb particles now melts at increased temperatures T_f>T_f~0. Transmission electron microscopy gives strong indicatings as to the origin of the change in melting behaviour; strains in the as-prepared material do not recover during cycling through T_f, and resolidification of the molten particles in the strained matrix brings the particles back to the initial structure with curved interfaces and small, but noticeable, misalignments relative to the cube-on-cube orientation relationship. Annealing leads to strain relief and to faceted Pb particles. The relation between strains and particle morphology is discussed.