Bereiche | Tage | Auswahl | Suche | Downloads | Hilfe

DF: Dielektrische Festkörper

DF 8: Relaxoren und heterogene Systeme

DF 8.1: Hauptvortrag

Donnerstag, 29. März 2001, 14:30–15:10, S18/19

NMR in Relaxors and Dipolar Glasses — •Robert Blinc — J. Stefan Institute, University of Ljubljana, Ljubljana, Slovenia

The local structure of ferroelectric relaxors and dipolar glasses is characterized by the local polarization distribution function W(p) and its moments which can be probed by the quadrupole perturbed NMR frequency ν or chemical shift of a given nucleus. The NMR lineshape is a frequency distribution f(ν) which reflects W(p). Comparison of theoretical and experimental data for f(ν) yields the local structure of disordered systems and allows for the determination of the Edwards-Anderson order parameter. Different forms of W(p) are obtained for Ising-type dipolar glasses, quadrupolar glasses, inhomogeneous ferroelectrics or spherical glass systems. We report on the ²⁰⁷Pb, ⁴⁵Sc, and ⁹³Nb NMR spectra of the perovskite relaxor single crystals PbMg_1/3Nb_2/3O₃, PbSc_1/2Nb_1/2O₃ and PbSc_1/2Ta_1/2O₃. Comparison with the ⁸⁷Rb, ²H, and ³¹P NMR lineshapes of the deuteron glass Rb_x(ND₄)_1−xD₂PO₄ shows that perovskite relaxors can be described as spherical glasses, whereas deuteron glasses are Ising-type glasslike. In both cases the random bonds dominate the random fields.