Surface of (NH₄)₃H(SeO₄)₂ crystals and its evolution in the course of the transition from the ferroelastic to the superprotonic phase were studied by optical polarization microscopy, scanning electron microscopy (SEM), atomic force microscopy (AFM), and energy-dispersive X-ray spectroscopy (EDXS). The morphology of fresh cleavage surfaces was examined. The composition and local electrical properties of the surface crystal layers were investigated. Local measurements of current-voltage curves and piezoresponse hysteresis loops were carried out. A transition to the phase with a superprotonic conductivity was proved to exist at T ≈ 308 K. A thin crystal layer of varying composition was found to form owing to topochemical reactions. Phase transformations and solid-state reactions at the crystal surface were analyzed based on the data obtained.

（NH ₄）₃ H（SeO ₄）_2的表面通过光学偏振显微镜，扫描电子显微镜（SEM），原子力显微镜（AFM）和能量色散X射线光谱（EDXS）研究了从铁弹性相到超质子相过渡过程中的晶体及其演化。检查了新鲜卵裂表面的形态。研究了表面晶体层的组成和局部电学性质。进行了电流-电压曲线和压电响应磁滞回线的局部测量。证明在T≈308 K处存在具有超质子电导率的相变。由于拓扑化学反应，发现形成了具有不同组成的薄晶体层。根据获得的数据分析晶体表面的相变和固态反应。