- It has long been known that the melting temperature Tm of close-packed metals correlates well with the monovacancy formation energy. However, with the possible exception of the face-centered-cubic metals, there is a prior phase transition from a mechanically brittle solid phase to a ductile phase. Here the likely role of disclinations in the brittle-ductile phase change is stressed. The present picture may help to understand the brittle-ductile transition not only in crystalline materials but also in amorphous phases. The structure of such phases can probably be characterized in terms of a disordered disclination network. As examples of elemental crystalline solids, Si and graphite are finally discussed, with the melting under pressure of graphite being quantified. 2004 Taylor and Francis Ltd.