Raman spectroscopic study of mixed valence neodymium and cerium chloride solutions in eutectic LiCl–KCl melts

Abstract

We have studied the Raman spectra of (NdCl₂)–(NdCl₃) and Ce–(CeCl₃) mixtures in eutectic (LiCl)_0.58(KCl)_0.42 as solvent in the temperature range up to 600 °C. For the highly corrosive samples a windowless cell in connection with a Raman microscope was utilised. To our knowledge the Raman spectra of the solutions of NdCl₂, CeCl₃ and (most likely) CeCl₂ in eut.–LiCl–KCl are shown here for the first time. In accordance with other rare earth halides described in the literature the Raman spectra of the pure trivalent systems are dominated by octahedral LnCl₆³⁻ species which show a typical broad polarized band centred at 245 cm⁻¹ for NdCl₃ and 240 cm⁻¹ for CeCl₃, respectively. NdCl₂ in (LiCl–KCl)_eu shows a complex Raman spectrum consisting of depolarized bands. In mixtures of divalent and trivalent neodymium chlorides both spectra can be observed in parallel and no additional Raman bands appear. Solutions of cerium in CeCl₃–(eut.–LiCl–KCl) show temporarily new Raman bands which are presumably due to divalent cerium chloride. These bands disappear in our samples after about 1 h since CeCl₂ is not stable under the experimental conditions. Our findings are discussed in the light of the strongly different electronic transport properties in the neodymium and cerium systems.