Impurity-induced van der Waals transition during decohesion

We investigate the thermodynamics of impurity segration between the separating atomic planes of a decohering solid from first principles. We find that the traction curve for decohesion at constant impurity chemical potential differs qualitatively from that at constant impurity concentration. In fact, for hydrogen and oxygen segregation between separating (111) planes during decohesion of fcc aluminum, a first-order van der Waals transition is predicted above a critical impurity chemical potential that results in a dramatic drop in the maximum stress of decohesion.