Correlation between electric-field-induced phase transition and piezoelectricity in lead zirconate titanate films

We observed that electric field induces phase transition from tetragonal to rhombohedral in polycrystalline morphotropic lead zirconate titanate (PZT) films, as reported in 2011 for bulk PZT. Moreover, we evidenced that this field-induced phase transition is strongly correlated with PZT film piezoelectric properties, that is to say the larger the phase transition, the larger the longitudinal piezoelectric coefficient d 33,eff . Although d 33,eff is already comprised between as 150 to 170 pm/V, our observation suggests that one could obtain larger d 33,eff values, namely 250 pm/V, by optimizing the field-induced phase transition thanks to composition fine tuning

Influence of Field-Induced Phase Transition on Poly(Vinylidene Fluoride-Trifluoroethylene-Chlorotrifluoroethylene) Strain

This work is focused on understanding the reasons behind the large electrostrictive strain of poly(vinylidene fluoride-trifluoroethylene-chlorotrifluoroethylene) terpolymer. Although a few explanations have been proposed in the literature, it remains largely unclear. Here, the role of an electrically induced phase transition is investigated. The strain in the crystalline part of the polymer is monitored using XRD while an electric field is applied onto the sample. Three regions of interest are clearly evidenced and, of particular interest, we observe a change in crystal symmetry located on the 30-70 V μm-1 range. In that region, the lattice progressively loses its hexagonal symmetry and moves toward the phase usually observed at lower temperature, with a higher polar order. In parallel, we conduct macroscopic strain measurements to compare to the XRD data. Three different regimes are also observed with a sudden increase in electrostrictive coefficient on the 30-70 V μm-1 interval, going from 19 to 33 m4C-1. This corresponds to a 1% strain, i.e., 25% of the total deformation measured at 100 V μm-1. By thoroughly comparing macroscopic strain and x-ray measurements, we are able to single out and quantify the impact of this field-induced phase transition in the polymer overall strain.P.L. and E.D. thank FNR (Fonds National de la Recherche) for partly funding this research through the project CAMELHEAT C17/MS/11703691/Defay. Sylvie Tencé-Girault’s contribution is achieved within the frame-work of the Industrial Chair Arkema (Arkema/CNRS-ENSAM-Cnam)

«La relation de limitation et d’exception dans le français d’aujourd’hui : excepté, sauf et hormis comme pivots d’une relation algébrique »

L’analyse des emplois prépositionnels et des emplois conjonctifs d’ “excepté”, de “sauf” et d’ “hormis” permet d’envisager les trois prépositions/conjonctions comme le pivot d’un binôme, comme la plaque tournante d’une structure bipolaire. Placées au milieu du binôme, ces prépositions sont forcées par leur sémantisme originaire dûment métaphorisé de jouer le rôle de marqueurs d’inconséquence systématique entre l’élément se trouvant à leur gauche et celui qui se trouve à leur droite. L’opposition qui surgit entre les deux éléments n’est donc pas une incompatibilité naturelle, intrinsèque, mais extrinsèque, induite. Dans la plupart des cas (emplois limitatifs), cette opposition prend la forme d’un rapport entre une « classe » et le « membre (soustrait) de la classe », ou bien entre un « tout » et une « partie » ; dans d’autres (emplois exceptifs), cette opposition se manifeste au contraire comme une attaque de front portée par un « tout » à un autre « tout ». De plus, l’inconséquence induite mise en place par la préposition/conjonction paraît, en principe, tout à fait insurmontable. Dans l’assertion « les écureuils vivent partout, sauf en Australie » (que l’on peut expliciter par « Les écureuils vivent partout, sauf [qu’ils ne vivent pas] en Australie »), la préposition semble en effet capable d’impliquer le prédicat principal avec signe inverti, et de bâtir sur une telle implication une sorte de sous énoncé qui, à la rigueur, est totalement inconséquent avec celui qui le précède (si « les écureuils ne vivent pas en Australie », le fait qu’ils « vivent partout » est faux). Néanmoins, l’analyse montre qu’alors que certaines de ces oppositions peuvent enfin être dépassées, d’autres ne le peuvent pas. C’est, respectivement, le cas des relations limitatives et des relations exceptives. La relation limitative, impliquant le rapport « tout » - « partie », permet de résoudre le conflit dans les termes d’une somme algébrique entre deux sous énoncés pourvus de différent poids informatif et de signe contraire. Les valeurs numériques des termes de la somme étant déséquilibrées, le résultat est toujours autre que zéro. La relation exceptive, au contraire, qui n’implique pas le rapport « tout » - « partie », n’est pas capable de résoudre le conflit entre deux sous énoncés pourvus du même poids informatif et en même temps de signe contraire : les valeurs numériques des termes de la somme étant symétriques et égales, le résultat sera toujours équivalent à zéro

In-situ X-ray diffraction on functional thin films using a laboratory source during electrical biasing

International audienceAmethodology that allows the quantification of structural changes in functional thin films during the application of external electrical field is reported. The originality of this method is the development of a set-up using a laboratory X-ray source since most of previous Operando studies have used synchrotron radiations. Several technical challenges have been addressed the (i) optimization of the electrical contact and the sample geometry within the lab-source goniometers, (ii) evaluation of any X-ray dose effect on the Metal/Insulator/Metal structure to prevent eventual charge accumulation at the electrode interfaces and (iii) the quantification of the effect of the time-delay, needed for X-ray measurement, on domain switching. The validity of our method has been demonstrated on a prototypic sol-gel lead zirconate titanate (PZT) thin film where the polarization and structural changes have been simultaneously measured. The evolution of ferroelastic domains as a function of external electric field has been quantified and two different effects have been successfully separated (a) the cell extension and (b) domain wall motion described as the switching between a and c tetragonal domains

3D strain imaging in a single sub-micron Au grain: a coherent X-ray diffraction analysis

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Effect of electrically induced cracks on the properties of PZT thin film capacitors

International audienceWe present a study of the effect of electrically induced cracks on both the ferroelectric and piezoelectric properties of Pt/PbZr0.52Ti0.48O3 (PZT)/Pt capacitors and correlations with domain structures of PZT films. Above a threshold bipolar electric field, cracks appear inside the PZT layer thickness leading to an increase in the ferroelectric polarization (+50% for the remnant polarization, from 16 to 25 μC/cm2) and the longitudinal piezoelectric coefficient d33,f (from ∼150 to ∼220 pm/V). The use of x-ray diffraction during in situ biasing provides direct evidence for a modification of the PZT crystalline structure as well as the a/c domain configuration. After cracking, the fraction of c-domains is strongly increased, thus contributing to higher polarization and larger strain in the out-of-plane direction. © 2022 Author(s)

3D strain imaging in sub-micrometer crystals using cross-reciprocal space measurements: Numerical feasibility and experimental methodology

International audienceDirect inversion of coherent X-ray diffraction patterns is a powerful method to image strains in individual crystals with a high spatial resolution, less than 10 nm. The possibility to invert the diffraction pattern is in principle ensured by the oversampling of the measurement. In addition, the resolution of the reconstructed object requires the measurement of the intensity distribution as far as possible in reciprocal space. Thus, fulfilling the oversampling and resolution constraints, in 3D, implies very long acquisition times, hardly compatible with the stability of the X-ray synchrotron source or sample. To overcome this problem, we present a method based on partial crossed intensity measurements: it consists in two irregularly spaced intensity measurements taken in two orthogonal directions. This paper demonstrates that partial crossed intensity measurements are in principle sufficient to reconstruct 2D objects using a phase retrieval algorithm. We also describe how such measurements can be achieved in practice for 3D imaging. 3D intensity measurements taken in two orthogonal directions for a 111 Bragg peak of a sub-micrometer Au grain are shown

Dislocation storage in single slip-oriented Cu micro-tensile samples: New insights via X-ray microdiffraction

Synchrotron X-ray microdiffraction was used to characterize the deformation structure of single crystalline Cu micro-tensile specimens which were oriented for single slip. The 3-mm thick samples were strained in situ in a scanning electron microscope (SEM). Electron microscopy observations revealed glide steps at the surface indicating single slip. While the slip steps at the surface must have formed by the predominant activation of the primary glide system, analysis of Laue peak streaking directions revealed that, even at low strains, dislocations had been activated and stored on an unpredicted slip system. Furthermore, the mLaue scans showed that multiple slip takes over at a later state of deformation