Interconnection of defect entropies and enthalpies in BaF2 revisited

Here, we investigate the following key prediction of a thermodynamical model that interrelates the defect parameters with the bulk elastic and expansivity data: for various defect processes in a given matrix material, a proportionality exists between defect entropies and enthalpies. The investigation is focused on BaF2 for which ab initio calculations within density functional theory and the generalized-gradient approximation have been recently made as far as the formation and migration of intrinsic defects are concerned, as well as for the elastic constants. Four defect processes have been studied in BaF2: anion Frenkel formation, fluorine vacancy migration, fluorine interstitial motion and electrical relaxation associated with a single tetravalent uranium. For these processes, the entropies and enthalpies vary by almost two orders of magnitude and reveal a proportionality between them. We find that this proportionality is solely governed by the bulk elasticity and expansivity data, which conforms to the aforementioned thermodynamical model.

THE TEMPERATURE DEPENDENCE OF VACANCY GIBBS FORMATION ENERGY FOR α-ZIRCONIUM

In this paper, we show that by using a thermodynamic model which interconnects point defect parameters with bulk elastic and expansivity data, we successfully estimate the temperature dependence of the Gibbs energy for vacancy formation in α-zirconium. Based on the recent elastic data, the model leads to the values of the ratio of the formation entropy over formation enthalpy, at various temperatures, that compare well with reported ones.