PROTON GLASSY BEHAVIOR IN RB1-X(NH4)XH2ASO4 MIXED-CRYSTAL

The mixed crystal Rb1-x(NH4)xH2AsO4 of ferroelectric RbH2AsO4 and antiferroelectric NH4H2AsO4 has been investigated for several values of x by measuring the dielectric constant along the a and c axis in the temperature range from 30 to 200 K. The phase boundary between the ferroelectric phase and the proton glass state is found to be between 0.13 and 0.20, and a similar boundary between the proton glass state and the antiferroelectric phase is observed to be located between 0.44 and 0.49. For samples with 0.23 x 0.44, the dielectric data can be scaled using the Vogel-Fulcher law with a static freezing temperature T0. From our experimental results, we construct a phase diagram of Rb1-x(NH4)xH2AsO4. © 1990 The American Physical Society.