Pressure dependence of the coexistence of proton-glass and ferro-antiferroelectric order in Rb1-x(NH4)xH2AsO4

Abstract

The effects of hydrostatic pressure, temperature and frequency on the dielectric properties and phase transitions of the material system Rb1-x(NH4)xH2AsO4 (RADA) in the composition range 0.10 ≤ x ≤ 0.40 have been investigated. This system exhibits coexistence of both ferroelectricJproton-glass and antifefroelectricJproton-glass behavior. Results on compositions in both regimes are presented and discussed, and the pressure-temperature phase diagrams are determined. By analogy with our earlier results on other hydrogen-bonded crystals, the present results indicate that all proton ordering will vanish below ∼ 20 kbar, but the disordered O—H c O bond network which is responsible for the formation of the proton-glass phase will persist to higher pressures than does the long-range order which is responsible for either the ferroelectric or antiferroelectric phases. The temperature dependence of the dipolar relaxation process associated with the glass transition is represented by the Vogel-Fulcher equation, and the pressure dependences of the parameters of this equation are evaluated and discussed. All the results can be qualitatively understood in terms of a decrease in the potential barrier seen by the proton as it moves along the hydrogen bond.