Surface Evolution at the Phase Transitions in (NH4)3H(SeO4)2 Crystals

The (NH 4 ) 3 H(SeO 4 ) 2 crystals in the temperature range of 296–343 K and the evolution of their surface at phase transitions have been studied by atomic force microscopy. Data on morphology and local electrical characteristics of crystal surface are obtained. Local current–voltage characteristics are measured, and the existence of structural phase transition to the phase with superprotonic conductivity at T ≈ 308 K is confirmed. A layer of non-conducting phase of variable composition is shown to appear on the crystal surface at the phase transitions.