Vibrational Behavior of Nanocrystalline Materials

The elastic and vibrational properties of iron-nickel and aluminum nanoparticles and nanocrystalline materials have been investigated on the basis of molecular dynamics simulations and the embedded atom method for the description of the materials. It is well known that nanocrystalline solids, with grain sizes in the nanometer range, exhibit often unsual properties like increased hardness due to immobilization of dislocations at the grain boundaries known as Hall-Petch effect. However, when reducing the grain size below a critical value, sliding processes between the grains decrease the hardness giving rise to the reverse Hall-Petch effect. Furthermore, the structural transformation of the particles and nanocrystalline materials, including melting of the nanoparticles, as a function of time, temperature or pressure show a distinct size dependence.