NUCLEAR-QUADRUPOLE DOUBLE-RESONANCE STUDY OF THE SOLID-SOLUTION RB1-XTLXH2PO4

The solid solution Rb1-xTlxH2PO4 has been investigated by the nuclear-quadrupole double-resonance methods. The Rb-87 nuclear quadrupole resonance (NQR) spectrum in the solid solution Rb1-xTlxH2PO4 exhibits for x > 0.2 the concentration dependences of the linewidth and of the center frequency characteristic for homogeneously mixed samples. The Rb-87 NQR spectra as measured in a mixed sample with a low concentration of rubidium ions (x = 0.98) show that the antiferroelectric phase transition in TIH2PO4 is associated with the condensation of two displacement waves. In a mixed sample with the concentration x of TIH2PO4 of 0.9, a phase transition is observed at nearly the same temperature as in TIH2PO4. NO phase transition is observed in the mixed crystals with the concentration x of TIH2PO4 between 0.2 and 0.8. The shape of the 5/2-3/2 transition line in the O-17 NQR transition spectrum is used for the determination of the Edwards-Anderson order parameter q(EA). The temperature dependences of q(EA) in Rb0.5Tl0.5H2PO4 and in Rb0.8Tl0.2H2PO4 demonstrate that we are in both cases dealing with a random-field smearing of a random-bond-type pseudospin spin-glass transition.