Analysis of electromechanical behaviour of (1-x)PMN-xPT (with x ≤ 0.1) bulk ceramics

The electromechanical behaviour of the (1-x)PMN-xPT (x less than or equal to 0.1) bulk ceramics is studied in particular through the sensitivity of its nanostructure to the electric field, stress and temperature. At first, it was shown by deviation to the Curie-Weiss type behaviour that a local polarisation appears at a T-d temperature (around 200 degrees C) i.e. largely above the temperature of the maximum of permittivity (T-m, respectively -13 degrees C and +36 degrees C for x = 0 and 0.1), which is consistent with the nucleation of polar clusters within a paraelectric matrix. Moreover, the dielectric relaxation observed for 0.9PbMg(1/3)Nb(2/3)O(3)-0.1PbTiO(3)-0.12MgO, in a large frequency range (100 Hz 15 MHz), and corresponding to a multi-Debye process with broadening of the relaxation time distribution as the temperature decreases, has been correlated to a nucleation and growth mechanism of polar clusters with decreasing temperature below T-d, which might result from the successive transitions of different compositions. This hypothesis has been confirmed by nanoanalysis thanks to EDXS and EELS techniques: in fact large fluctuations of the local composition around the nominal one have been revealed, lead and magnesium deficient areas enriched in niobium coexisting with nanodomains (around 10 nm) strongly enriched in lead acid slightly in magnesium. Consequently, due to such heterogeneities, the material remains mainly paraelectric up to very low temperatures. This effect can be balanced by the application of a high electric field which induces the growth of the polar clusters up to a macroscopic ferroelectric transition for some conditions of temperature and electric field. The specific electromechanical characteristics of 0.9PMN-0.1PT are reported, in particular the strong dependence of their elastic compliance with the electric field, the prestress applied to the material and the temperature. This behaviour is attributed to the growth of compliant polar clusters induced by decreasing temperature or increasing electric field and inhibited by the application of a uniaxial stress. Finally, as 0.9PMN-0.1PT bulk ceramics are characterised by a tunable compliance, their potential interest as active vibration control is presented and its electromechanical behaviour as actuator, under a sinusoidal electrical signal added to a 0.6 kV/mm DC electric field, is characterised. (C) 2000 Elsevier Science Ltd and Techna S.r.l. All rights reserved.