Coexistence of proton-glass and ferroelectric order in Rb1-x(NH4)xH2AsO4.

The mixed crystal Rb~ —„(NH4)„HzAs04 (RADA) has been investigated for several values of x(x =0, 0.12, 0.15, and 0.20) by measuring the complex dielectric permittivity along the a tetragonal axis in the temperature range from 3 to 300 K and frequency range from 1 Hz to 30 kHz. We find coexistence of ferroelectric and proton-glass order in RADA for x =0.12 and probably at x 0.15. The long-range ferroelectric order is not destroyed by the onset of proton-glass ordering. This behavior is similar to that of other proton-glass systems and of the magnetic Ising glass systems reported by Wong etal. in Feo»Mg0. 45C12 and by Yoshizawa etal. in Fe Mn] —~Ti03. The partial phase diagram for Rb~-„(NH4)„HzAs04 including the coexisting proton-glass and ferroelectric phases is presented.