Oriented growth and crystal structure of phases precipitated in Eu²⁺-doped NaCI single crystals

X-ray investigations of Eu²⁺-rich precipitates in NaCl single crystals have revealed the presence of two phases. Phase A of chemical formula EuCl₂ with a CaF₂-type structure and lattice parameter a = 6.969 (2) Å preserves strictly the orientation of the matrix lattice. Phase B with the lattice parameter a = 7.47 (1) Å and tentative formula EuCl₂.2NaCl, containing Eu²⁺ ions and charge-compensating cation vacancies, is localized at subgrain boundaries and is thermally less stable than phase A.