Thermal analysis was applied to determine liquidus temperatures in the CsCl-PbCl2 (18.3 -81.7 mol%) eutectic mixture with the PbO concentrations ranging from 0 to 20 mol%. The temperature dependence of the PbO solubility in the CsCl-PbCl2 (18.3-81.7 mol%) eutectic melt was studied, and the thermodynamic parameters of the PbO dissolution were calculated. The type, morphology, and composition of oxychloride ionic groupings in the melt were determined in situ using Raman spectroscopy. (C) The Author(s) 2017. Published by ECS. All rights reserved.