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

It is shown that collective glassy behavior occurs not only in strongl y substitutionally disordered systems as assumed so far, but also in w eakly 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 descr ibed quantitatively by the compressible random bond-random field pseud ospin Ising model, showing a much greater random bond than random fiel d effect even for x --> 0. A discontinuous change in the Edwards-Ander son order parameter has been observed at the transition temperature wh ere ferroelectric long range ordering occurs as predicted by theory.