Dynamical Fluctuations in a Dipolar Glass

Abstract

Other reports in this symposium have focused on the static properties of defects near a structural phase transition. A different set of questions surrounds the dynamic behavior of such systems. KTaO₃:Nb, or KTN, is one such system of particular interest where, due to the availability of high quality materials, it may be possible to make quantitative contact between the behavior of defects in the dilute limit and the effects of similar defects at concentrations where they affect the macroscopic behavior of the order parameter. We have previously shown¹ that the average radius ξ of the ferroelectrically distorted microregions surrounding symmetry breaking defects in nominally pure KTaO₃ is directly related, as a function of T, to the phase diagram of KTa_(1-x)Nb_xO₃ (KTN) in the Tx plane. That is, the phase transition to long range ferroelectric order at high concentration x occurs when ξ(T _c )=An ^0.33, where n is the number density of Nb ions, and A is a constant very close to unity. Thus, the structural phase transition occurs when the distorted regions overlap continuously.