Spatial distribution of europium chloride precipitates in NaCl : Eu 2+ crystals as determined by epifluorescence optical microscopy

The spatial distribution of fluorite-type EuCl 2 particles and EuCl 2 (111)- and EuCl 2 (310)-like platelets precipitated in well-annealed NaCl : Eu 2+ single-crystals was determined by epifluorescence optical microscopy with the aid of three-dimensional physical models. X-ray diffraction Laue patterns and optical spectroscopy were used to confirm the single-crystal character of the specimens and to monitor the precipitation dynamics during annealing. Precipitates smaller than 0.28 µm were found to exist across all the crystal host (4.0 2 10 11 precipitates cm 3 ), while precipitates ranging from 0.28 to 0.45 µm in size were found to exist along linear structural singularities of the matrix (1.2 2 10 4 precipitates cm m 1 ). These singularities, identified as crystal edge dislocations about 10.0 µm in length, were found to be periodically arranged, forming wall-like groups of dislocations along subboundaries between crystal domains with a misorientation value of about 0.9". Europium-decorated dislocations are accompanied by europium exhaustive matrix zones, indicating that impurity segregation processes are involved during precipitation phenomena.