Single-crystal proton glasses

Results obtained on mixed crystals of Rb1-x(NH4)xH2PO4 are reported. These polar materials of the KH2PO4 family are characterized by a high-temperature disordered network of 0-H-0 bonds. On cooling, different orderings of these bonds correspond to th onset of a ferroelectric polarization parallel to the tetragonal c-axis in RbH2PO4 (x=O), or of antiferroelectric moments perpendicular to it in NH4H2PO4 (x=l). In the mixed crystals of interest, these transitions are suppressed by random NH4 substitutions. The NH4+ ions form H-bonds with nearby PO4 tetrahedra, occupying 0-sites and frustrating the low-temperature acid-proton order. Glass behavior results over a broad range of concentration 0.22 < x < 0.8.1,2. © 1984, Taylor & Francis Group, LLC. All rights reserved.