AS-75 NUCLEAR-QUADRUPOLE RESONANCE IN WEAKLY SUBSTITUTIONALLY DISORDERED RB1-X(NH4)XH2ASO4

It is shown that collective glassy behavior occurs not only in strongly substitutionally disordered systems as assumed so far, but also in weakly disordered systems, namely, Rb1-x(NH4)xH2AsO4 with x = 0.01 and x = 0.02. The observed As-75 NQR and NMR line shapes can only be described quantitatively by the compressible random bond-random field pseudospin Ising model, showing a much greater random bond than random field effect even for x --> 0. A discontinuous change in the Edwards-Anderson order parameter has been observed at the transition temperature where ferroelectric long range ordering occurs as predicted by theory.