High-temperature phase transitions in the improper ferroelectric KIO3

The ac conductivity (sigma(ac)) and dielectric permittivity (epsilon) are determined in the temperature range 300 K < T < 520K at some selected frequencies (0.5-10 kHz) for the polycrystalline samples of KIO3 compound. The results indicated that the compound behaves as an improper ferroelectric and undergoes a ferroelectric phase transition from a high temperature rhombohedral phase I to a low temperature monoclinic phase II at T-c (486 +/- 1) K. A second structural phase transition was observed around 345 K. The conductivity varies with temperature range and for T > 428K intrinsic conduction prevails. Different activation energies in the different temperature regions were calculated. The frequency dependence of sigma(omega) was found to follow the universal dynamic response [sigma(omega)alpha(omega)(s(T))]. The thermal behaviour of the frequency exponent s(T) suggests the hopping over the barrier model rather than the quantum mechanical tunneling model for the conduction mechanism.