Thermal properties and phase transitions of heavy rare-earth fluorides
Sergei Stankus, Rashid Khairulin, Konstantin Lyapunov
The experimental data on the thermal properties of the solid and liquid trifluorides of gadolinium, dysprosium, holmium, erbium, ytterbium, lutetium, and yttrium have been summarised and discussed. The analytical treatment of the results has shown that the linear dependence of the melt molar volume on the radius of cation established previously for the light rare-earth fluorides (REFs) ceases to be true for the heavy REFs (beginning with HoF3). The coefficients of thermal expansion (TECs) of the melts in the GdF3 – LuF3 series are diminished as the size of cation decreases, whereas the values of the melt TECs of the light REFs coincide within the limits of errors. These facts point to progressive variation of the liquid structure in the GdF3 – LuF3 series. A possible reason for this structure variation is that cation coordination number in the melt reduces as the size of cation decreases.