The electromechanical behaviour of the (1–x)PMN–xPT (x⩽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 Td temperature (around 200°C) i.e. largely above the temperature of the maximum of permittivity (Tm, respectively −13°C and +36°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 0.9PbMg1/3Nb2/3O3–0.1PbTiO3–0.12MgO, 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 Td, 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 and 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.

(1 - x)PbMg1/3Nb2/3O3-xPbTiO3 ceramics with x = 0, 0.1 were prepared with a 12 mol% MgO excess to obtain dense and perovskite phase materials after sintering. The dielectric characterization has revealed that a local polarization appears at a Td temperature largely above the temperature of the maximum of permittivity (Tm, respectively -13 ○C and +36 ○C for x = 0 and 0.1). This phenomena is consistent with the nucleation of polar clusters. Moreover, a dielectric relaxation is observed for 0.9PMN-0.1PT-0.12MgO, in a large frequency range (100 Hz – 1 GHz), which corresponds to a multi-Debye process with broadening of the relaxation time distribution as the temperature decreases. This suggests a nucleation and growth mechanism of polar clusters with decreasing temperature, which can result from the successive transitions of different compositions. This hypothesis was confirmed by the identification of large chemical heterogeneities on a nanometric scale by TEM using two spectroscopy techniques (EDXS and EELS), because of the association of low and high atomic number elements in the materials, different types of equipment and also the simulation of the patterns with standards. In fact, these quantitative analyses have revealed large fluctuations of the local composition around the nominal one: lead and magnesium deficient areas enriched in niobium coexist with nanodomains largely enriched in lead and slightly in magnesium, which the size depends on the titanium content. The origin of these heterogeneities in correlation with the reactions sequences during calcination and sintering is discussed: in particular the addition of titanium contributes, by stabilizing the perovskite phase, to limit the diffusion of lead oxide, which consequently increases the homogeneity of the ceramics. 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 by displacement of their interface with the paraelectric matrix and orientation of their polarization in the direction of the electric field which can lead to a macroscopic ferroelectric transition in specific conditions of temperature and electric field intensity. These different mechanisms relax in a frequency range which depends on the temperature and on the amplitude of the electric field.

The global and local chemical composition of Nicalon fibres present in as- fabricated and annealed SiC-C-SiC composites are analysed by Analytical Transmission Electron Microscopy. EDXS, EELS, HREM and electron diffraction are used to characterise the fibre, which consists of different nanophases containing carbon, oxygen and silicon. Special attention is paid to the quantitative analysis of carbon and oxygen; different data treatment in EDXS and EELS are evaluated and compared. The limitations of the analysis techniques are discussed. The global composition of the core and the periphery of the fibre in the as-fabricated composite is determined to be: 57.5 wt% Si, 29 wt% C, 13.5 wt% O (38.6at% Si, 45.5at% C, 15.9at% O) and 53 wt% Si, 32 wt% C, 15 wt% O (34.4at% Si, 48.5at% C, 17.1at% C), respectively. After annealing in atmospheres with different oxygen partial pressures, the global oxygen content in the (fibre changes. The fibre constituents are silicon carbide nanocrystals, graphite units and an amorphous silicon oxycarbide phase.

Secondary ion mass spectrometry (SIMS) is a well adapted analytical method for the chemical characterization of concentration profiles in layered or multilayered materials, particularly concerning the more or less abrupt interfaces bounding those layers. It is known that the fiability and accuracy of the interface characterization may be affected by methodological factors, which alter the depth resolution such as: macroscopical or microscopical initial roughness of the substrate and/or of the layers, ion-induced roughening, effects of differential sputtering of the various elements, transitory stage of the primary ion beam implantation, ion beam induced accelerated diffusion, balistic mixing or segregation; etc...This communication describes several examples of SIMS analysis performed on metal multilayers (Co/Cu) and on epitaxial semiconductor layers (CdTe/GaAs), focussing the interest on the particular analytical problems raised by the initial roughness and the ion induced roughening effect. The interpretation of the measured profiles, the influence of analytical parameters (such as the nature of the primary ion beam, sputtering conditions, detected ion species), and the limitations of profilometry roughness measurements, are discussed. Solutions are proposed in order to improve the depth resolution of interface characterization, including a tentative modelization of roughness effects.