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The Raman features of neptunium dioxide (NpO2) and uranium–neptunium mixed oxides were investigated. Raman spectra of 16O and 17O-NpO2 enriched sample were measured with excitation energy range of Ei = 1.91–2.54 eV. Raman spectra of both NpO2 samples and the uranium–neptunium rich mixed oxides show an asymmetry at low energies of the Γ25′ (T2g) mode. The asymmetry was evidenced to originate from an electronic band at 431 cm–1 which originates from crystal field splitting. This assignment is in good agreement with theoretical models for NpO2 with the hypothesis that the electron–phonon bound state is decoupled at high temperatures. The asymmetry of the Γ25′ mode can be considered as a fingerprint of the NpO2 lattice.

In this study we present the thermodynamic description of the binary CaF2–ThF4 system and the ternary LiF–CaF2–ThF4 system. In order to describe the general shape of the phase diagram, the phase equilibria of several intermediate compositions of the CaF2–ThF4 system have been measured for the first time in the present work using the DSC technique. These results have been combined with X-ray diffraction studies for the identification of the phases in equilibrium and for the determination of the structure of the CaThF6 compound. Considering all of the novel experimental data, the CaF2–ThF4 system has been assessed for the first time using the Calphad approach. Moreover, the ternary LiF–CaF2–ThF4 phase diagram has been calculated and optimized using the experimental data obtained in this study for the ternary mixtures. The model developed reproduces very well all the measurements performed and correctly predicts the lowest eutectic temperature and composition.

Using drop calorimetry we measured enthalpy increments of the LiF-KF, LiF-RbF and LiFCsF binary systems at temperatures above melting. 10 samples with different compositions (four compositions for LiF-KF, one composition for LiF-RbF and five compositions for LiFCsF) were prepared and measured between 884K and 1382 K. To protect the calorimeter from corrosive fluoride vapor at high temperature an encapsulating technique developed for this purpose was used. The samples were filled in nickel containers which were sealed by laser welding and afterwards used for the measurements. From the obtained results we derived the molar heat capacity functions of the respective samples. The heat capacities of the samples, having different compositions of the same binary system, were compared with the values for ideal behavior and the excess heat capacity function was determined for the whole composition range of the liquid solution. It was found that the excess heat capacities clearly depend on the cation radius and increases in the order LiF-NaF < LiF-KF < LiF-RbF < LiF-CsF., JRC.E.3-Materials research