We discuss some of the issues associated with the relation between the leakage current and the dielectric constant on the one hand, and the crystallographic structure and the chemical composition of the film on the other. Our focus is on dielectrics containing Pr oxides. Starting with the binary Pr2O3, we investigate electronic properties and formation energies of point defects as revealed by ab initio calculations and we attempt to associate this data with the experimental information on the influence of processing on the dielectric quality of the film. We then consider Pr silicates on Si for metal-oxide-semiconductor field effect transistors and PrxAl2-xO3 on TiN for metal-insulator-metal front-end applications. In the latter case, annealing above about 800 degrees C, needed to noticeably increase the effective dielectric constant, causes an increased leakage. Investigating this effect, in particular we discuss the diffusion mechanism for Ti and the influence of Ti on the leakage current, taking into account the stoichiometry dependence of defect formation energies and the position of electron transition states obtained from ab initio data. (C) 2008 The Electrochemical Society.