Structural, magnetic and spectroscopic investigations of europium oxychloride, EuOCl

The reaction of the ammonium halides (NH₄X, X^- = F^-, Cl^-, Br^-) with the rare earth (R) oxides (e.g. R₂O₃) is a convenient way to obtain the trihalides (RX₃) or stoichiometrically pure oxyhalides (ROX). Problems may arise with rare earths which can be easily reduced by the ammonia produced during the reaction. In this study, the products of the reaction between Eu ₂O₃ and NH₄Cl were investigated with the X-ray powder diffraction, Mössbauer and EPR spectroscopies and magnetic susceptibility measurements. The tetragonal crystal structure of EuOCl was refined with the Rietveld method. The Mössbauer and EPR spectra as well as the paramagnetic susceptibility measurements were analysed to detect the presence of divalent europium. The evolution of the paramagnetic susceptibility as a function of temperature was measured and compared to that calculated from previous spectroscopic measurements. Only the paramagnetic susceptibility measurements revealed beyond doubt the presence of divalent Eu²⁺ impurity.