Title: Defect entropies and enthalpies in Barium Fluoride,
Abstract: Various experimental techniques, have revealed that the predominant intrinsic
point defects in BaF$_2$ are anion Frenkel defects. Their formation enthalpy
and entropy as well as the corresponding parameters for the fluorine vacancy
and fluorine interstitial motion have been determined. In addition, low
temperature dielectric relaxation measurements in BaF$_2$ doped with uranium
leads to the parameters {\tau}$_0$, E in the Arrhenius relation
{\tau}={\tau}$_0$exp(E/kBT) for the relaxation time {\tau}. For the relaxation
peak associated with a single tetravalent uranium, the migration entropy
deduced from the pre-exponential factor {\tau}$_0$, is smaller than the anion
Frenkel defect formation entropy by almost two orders of magnitude. We show
that, despite their great variation, the defect entropies and enthalpies are
interconnected through a model based on anharmonic properties of the bulk
material that have been recently studied by employing density-functional theory
and density-functional perturbation theory.