Competing structural orderings and transitions to glass in mixed crystals of Rb1-x(NH4)xH 2PO4

Frustration is produced in crystals of the KDP family by mixing ferroelectric and antiferroelectric constituents. Birefringence and dielectric measurements are reported for 0 ≤ x ≲ 0.35. They indicate an interesting phase diagram, with a glassy phase probably preceded by a mixed phase for the upper part of the concentration range investigated. The randomness of the competing short-range interactions is likely to play a major role, making these structural glasses truly analogous to magnetic spin glasses.