Phases coexistence of hydrogen-bonded mixed ferroelectric and antiferroelectric crystals

The problem proton-glass and ferroelectric phases coexistence in Rb1-x(NH4)(x)H2AsO4 (RADA) and K1-x (NH4)(x) H2PO4 (KADP) crystals based on dielectric studies up to temperature 0.3 K is presented. The measurements were performed in the helium-3 cryostat in the temperature range from 300 K to 0.3 K. Glass behavior for the RADA is present even for a small concentration x = 0.01, whereas for the KADP the proton glass occurs for a concentration x > 0.05. The partial phase diagrams of RADP and KADP as a function of fractional ammonium concentration x and temperature T are presented.