Eur. Phys. J. B 16, 455-462 (2000)
https://doi.org/10.1007/s100510070203

Non ergodic aging in potassium niobo-tantalate crystals

¹ Laboratoire des Milieux Désordonnés et Hétérogènes (Associated with the Centre National de la Recherche Scientifique (UMR 7603)) , Université Pierre et Marie Curie, Case 86, 75252 Paris Cedex 05, France
² Departamento de Física, Universidade do Minho, 4709 Braga codex, Portugal

Corresponding author: ^a dous@ccr.jussieu.fr

Received: 17 November 1999
Published online: 15 August 2000

Abstract

Slow dynamics has been studied in various potassium niobo-tantalate crystals (KTN) by recording the complex dielectric constant after several thermal histories: isothermal evolution following controlled cooling or rapid quenching, positive or negative temperature cycles. The results reveal most of the behaviours of aging already found in lithium-potassium tantalate (KLT): effective ergodicity breaking (the asymptotic value of the dielectric constant varies as the logarithm of the cooling rate R), quasi-independence of the isothermal evolution with respect to a sojourn at lower temperature. But some differences between KTN and KLT are noticeable: coefficients of log|R| with opposite signs, role of the quenching temperature on the subsequent evolution, no overshot after a temperature jump. In order to explain the results we propose to extend the model initially developped for KLT taking into account the different nature of the low temperature phase, paraelectric for KLT and ferroelectric for KTN. In this model the variations of the dielectric constant are attributed to the slow movements of polarization domain walls hindered by static random fields. By measuring the dielectric constant during cooling and immediate heating at the same rate, an illustrative comparison is provided, showing that the evolution of the domain size is reversible in KLT and not in KTN.