Aging and domain growth in K1-xLixTaO3 (x <= 0.05)

We present experimental results on the dielectric constant in orientational glasses K1-xLixTaO3 (KLT) with x less than or equal to0.05, together with the detailed (analytic and numerical) study of a model which attributes the observed aging to the motion of the walls of polarization domains. We show that the dielectric constant after a positive temperature jump goes throug h a maximum as a function of the subsequent time. This observation and thos e previously reported (aging, cooling rate dependence, etc.) are compared w ith the predictions of the model, in which the variations of the dielectric constant are attributed to the change of polarization domain wall area. Th e total area decreases by domain growth and increases by nucleation of new small domains inside the larger ones. These two opposite variations are bot h hindered by static random fields (equivalent to energy barriers) due to t he frozen dipoles borne by the off-center Li+ ions. Many results are well e xplained by the model with a single energy barrier. However, some effects c an only be understood if a broad distribution of energy barriers is assumed . We use the experimental data to determine this distribution and find it t o be unimodal with a width comparable to its most probable value.