CURVATURE OF ARRHENIUS PLOTS OF DIFFUSION AND ITS DISAPPEARANCE UNDER PRESSURE WITH A SINGLE-VACANCY MODEL

In some metals the specific heat Delta cP (per single vacancy) associated with the temperature variation of the activation enthalpy h act is large and hence an Arrhenius curvature is detectable. It is shown that, at high pressures, the value of Delta cP reduces by a large factor and therefore the Arrhenius plot becomes a straight line. Furthermore, it is found that whenever Delta cP exceeds 35 k the presence of a second diffusion mechanism is obligatory.