A mechanism to explain the complete oxidation of small metal clusters is proposed, based on the occurrence of a mechanical instability driven by the expansion of the progressively oxidized cluster surface and the subsequent stress relaxation. Molecular dynamics simulations of spherical Pd clusters show that an expanded surface layer is capable of straining the inner core of the cluster up to the point of inducing cavitation. These findings allow the interpretation of recent experimental results in which oxidized Pd clusters exhibit a hollow spherical shape.

• Received 21 February 1996

DOI:https://doi.org/10.1103/PhysRevLett.77.2495