STROPHOIDAL ARGAND DIAGRAM AND THE DISTRIBUTION OF RELAXATION-TIMES IN K1-XLIXTAO3

We have studied the relaxation of off-center Li+ ions in KTaO3 by dielectric measurements on 1% and 1.5% crystals, from 20 Hz to 2 MHz and from 4 to 200 K. The shape of the epsilon'' vs epsilon' Argand diagrams demonstrates the existence of a distribution of relaxation times. In analogy with spin glasses, a new expression is proposed for the analysis of these diagrams, a strophoidal function, which leads to a distribution function D(theta) decreasing for large theta as theta-(1+alpha) with 0 < alpha < 1. The most probable relaxation time theta(mp) of the distribution follows an Arrhenius law with a barrier height close to 950 K.