Destabilization of icosahedral structures in FePt multiply twinned particles

In this paper, we report on the structural characterization of FePt nanoparticles utilizing high-resolution transmission electron microscopy (HRTEM). The nanoparticles are prepared by inert gas condensation and subsequent sintering in the gas phase. At certain preparation conditions, the particles exhibit unusual morphologies. HRTEM images show that, these "transition type" particles display clear signatures of icosahedral structures. On the other hand, they are not spherically symmetric, but rather elongated. HRTEM combined with contrast simulations prove that these particles consist of an icosahedral head which is, however, extended along one of its 5-fold symmetry axes. This finding is attributed to a decreased thermodynamic stability of icosahedra with respect to decahedral structures at increasing temperatures and particle sizes. (C) 2003 Elsevier B.V. All rights reserved.