Entropy and enthalpy of formation and migration of lattice defects in Na(I)

The self-diffusion coefficients of Na+ and I-, as well as the ionic conductivity, are measured in Na(I) single crystals, pure and doped with Ca2+ ions. The computer analysis of the whole set of data shows that the atom transport in Na(I) is ensured essentially by the free vacancies with a very small contribution (approximately 4%) of the vacancy pairs. The thermodynamic parameters of vacancy formation and migration are derived by taking the long range interactions into account (activity coefficients on the concentrations and relaxation factors on the mobilities). The respective entropies of Schottky defect formation, cation migration and anion migration are equal to 7.64, 3.23 and 2.91 k while the corresponding enthalpies are equal to 2.00, 0.58 and 0.77 eV. (author)