Phonon scattering and interstitial clusters in γ-irradiated LiF

The thermal conductivity of pure and Mg-doped LiF single crystals irradiated at room temperature in a Co⁶⁰ source (3–780 Mrad) was measured between 60mK and 70 K. Several phonon scattering mechanisms for extended defects are reviewed and it is shown that experimental results can be understood in terms of two types of interstitial clusters: (a) small spherical clusters whose number density and size depend on the residual impurity content; and (b) large non-spherical clusters of toroïdal shape with a major radius of several hundred Å and minor radius of some tens of Å. For increasing dose, the major radius decreases, the minor radius increases and the rings become increasingly opaque possibly due to the associated strain field.     

Transport processes in NaCl single crystals doped with a trivalent cation; solubility,association and migration of Y3+

The self-diffusion coefficient of ²²Na⁺ and the ionic conductivity are measured as a function of temperature in NaCl single crystals doped with labelled yttrium ions, as well as the diffusion coefficient of ⁸⁸Y³⁺. We give the theoretical equations for the transport processes in the alkali halides doped with a trivalent cation; These are derived from the theory of the crystals doped with divalent cations. Solubility of YCl₃ in NaCl is accurately determined through a radioactive technique. The free enthalpy of solubility of free Y³⁺ is: (2.91?13 kT) eV. A good fit of the whole set of data is obtained by treating the association between Y³⁺ ions and vacancies by the single equation $\text{K}{}_2\text{= 12}\text{exp}\text{(-9.5)}\text{exp}\text{(}\text{1.17}\text{kT}\text{)}$. The jump frequency of Y³⁺ is $\text{w}{}_2\text{= 1.37 × 10}{}^{13}\text{exp}\text{(-}\text{0.98}\text{kT}\text{)}\text{sec}{}^{-1}$. The results are compared to those characterising the divalent foreign cations.