Using atomic force microscopy in the study of superprotonic crystals

An investigation of new superprotonic crystals–namely, acid salts of potassium–ammonium sulfate (K$_{1-x}$(NH$_4$)$_{x}$)$_{3}$H(SO$_4$)$_{2}$, $x\ge$ 0.57 – is carried out. The surface morphology, domain structure, and conductivity of the samples are studied using atomic force microscopy. The stability and degradation of the surface of superprotonic crystals is first studied at the nanoscale. The data of piezoelectric response microscopy make it possible to establish that the crystal of (K$_{0.43}$(NH$_4$)$_{0.57}$)$_{3}$H(SO$_4$)$_{2}$ transits from the paraelectric phase to the ferroelectric phase when the temperature is decreased from 296 K to 282 K.