Cluster Dynamics in a Dipolar Glass

Abstract

We have directly observed fluctuating dipolar clusters in the mixed crystal K${\mathrm{Ta}}_{0.991}$ ${\mathrm{Nb}}_{0.009}$ ${\mathrm{O}}_3$ using inelastic-light-scattering techniques for temperatures between 1.8 and 25 K and for electric fields up to 2 kV/cm. Together with earlier dielectric-relaxation data, our data span over nine decades in frequency and obey a Vogel-Fulcher relaxation model over the temperature range 6-15 K with an extrapolated transition at 3.0 K to a glassy dipolar state.