High-temperature dielectric and conductivity behavior of K4LiH3(SO4)4

Measurements of conductivity and dielectric constant of K4LiH3(SO4)4 single crystal during consecutive thermal cycles are presented. Anisotropy of the conductivity is found to persist through all of the thermal cycles. Detailed analysis of temperature dependence of the conductivity measured during the first heating cycle shows that the superionic phase transition takes place at 425 K450 K as well as T∼425 K. After the first heating cycle, however, any change in the activation energy of the conductivity and pronounced anomaly in the dielectric constant are not observed. The irreversibility of the superionic phase transition in K4LiH3(SO4)4 seems to be related to the effect of thermal treatment applied to the fresh sample during the first heating cycle.