Structural phase transitions and electrical conductivity studies of (NH₄)₃H(SeO₄)₂ crystal

The electrical conductivity measurements were performed on single crystals of (NH₄)₃H(SeO₄)₂ in the temperature range of 25°C to 80°C along the c* axis. The crystal is found to be in a superionic state as it transforms to the high-temperature phase. The temperature dependence of the electrical conductivity of the sample crystal in the different phases follows the Arrhenius law. The increasing electrical conduction is due to the disorder of the oxygen atoms of the SeO₄ groups in the high-temperature phase. The proton ions can move among the sites which are the newly formed hydrogen bonds between the oxygen atoms of the nearest and next-nearest SeO₄ groups.