X-ray studies of the NaCl:SrCl₂ system

High-temperature diffraction experiments have been carried out on the NaCl: SrCl₂ system, both in its poly- and monocrystalline form. These experiments have led us to the determination of the dilution enthalpy of the SrCl₂ precipitates in the NaCl matrix (h_D = 0.90 ± 0.05 eV). Brauer's method was used to calculate the distortion around one defect and Eshelby's model was used to evaluate the resulting change in the lattice parameter due to these perturbing centers. The concentrations of defects calculated from these models are in good agreement with those determined chemically. Small-angle X-ray scattering experiments were performed on the same crystals, with suitable thermal treatments, to follow the clustering of defects as a function of the annealing temperature. It is possible to maintain a large amount of nearly dispersed strontium in the lattice by quenching the crystals from high temperature. The point defects agglomerate by successive annealings from 100 to 300°C, forming clusters of increasing sizes. A discussion of the composition of those centers is included.