Order parameter anisotropy in the glass phase of (RDA)1-x(ADA)xcrystals: experimental evidence

Abstract
The authors have studied the temperature dependence of dielectric constants in Rb1-x(NH4)xH2AsO4 mixed crystals for x=0.35 and x=0.49. A Rb0.51(NH4)0.49H2AsO4 crystal was observed to show a diffuse anti-ferroelectric phase transition instead of the glass transition of the Rb1-x(NH4)xH2PO4 systems (0.220.65(NH4)0.35H2AsO4 crystal, however, was observed to show the glass transition at Tg approximately=42 K with respect to the z-axis dielectric constant in 'z but no glass transition with respect to the x-axis dielectric constant in 'x until the temperature was lowered further to about 20 K. This anisotropy seems to be what Matsushita and Matsubara (1984) predicted for Rb1-x(NH4)xH2PO4 systems but has not been supported by previous experiments.