Thermal and dielectric properties of rare earth iodates

The thermal (TGA, DTA and DSC) and dielectric behaviour of all rare earth iodates (except prometheum) has been investigated. The iodates of lanthanum, cerium to europium and gadolinium to lutetium decompose differently and the activation energies for these decomposition reactions have been determined. The DSC measurements have shown that all of the anhydrous iodates undergo one or more exothermic/endothermic changes. From the nature of the DSC profiles, heat of transitions, and powder diffraction data the phase transformations of Ln (IO₃)₃ have been found to occur in four different ways (lanthanum, cerium to europium, gadolinium to terbium, dysprosium to lutetium). Dielectric measurements of Ln (IO₃)₃ at varying temperature have corroborated the observations made with DSC studies. Relatively low dielectric constants of the high-temperature phases probably indicate their centrosymmetric structures. The dielectric behaviour of noncentrosymmetric Ln (IO₃)₃·H₂O (Ln=cerium to samarium) has been investigated in the temperature range 30 to –160° C. They have high dielectric constants (_r, ~ 1800 to 2400) at the ambient temperature and do not show significant change in the entire temperature range of investigation.