Amorphisation compositional limits and atomic displacement in fcc solid solutions

Although amorphisation and melting processes are characterised by different thermodynamic and kinetic features, it appears that intimate connections exist between the two topological order–disorder transitions. Experimental and theoretical findings suggest that both static and thermal atomic displacements from crystalline lattice equilibrium positions are able to induce the loss of long-range order. In this paper, the relationship between the critical volume expansion at amorphisation compositional limits and the static atomic displacement is investigated. The volume expansion associated with the substitutional dissolution of B atoms into a given fcc crystalline matrix A is evaluated according to the simplified model of Egami and Waseda and compared with the volume reached by the pure matrix A at the melting temperature. The resulting volumes are used to calculate the average static atomic displacement induced by local elastic distortions of crystalline lattice. The static atomic displacement is then connected with the size ratio between solute and matrix atoms.