Annie Simon
Centre national de la recherche scientifique
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Featured researches published by Annie Simon.
Journal of Physics: Condensed Matter | 2004
Annie Simon; J. Ravez; Mario Maglione
We investigate the gradual crossover from ferroelectric to relaxor behaviour versus substitution in lead-free ceramics. We show that the Vogel?Fulcher law in the relaxor state is the extrapolation of the ferroelectric line. To explain this extrapolation, we suggest that both the host matrix and the impurity induced clusters are triggered by the BaTiO3 soft mode correlation length. The Ti?O bond oscillations are the key mechanism.
Journal of Materials Chemistry | 1999
J. Ravez; Cédric Broustera; Annie Simon
Relative permittivity studies of ceramics with a variety of compositions in the BaTiO 3 -BaZrO 3 -CaTiO 3 system showed some of them to be ferroelectric relaxors at temperatures close to 295 K. Such a favourable effect is due to the Ca 2+ for Ba 2+ cationic substitution. In addition a spontaneous classical ferroelectric-relaxor ferroelectric transition was evidenced. Some of these new compositions are of interest for applications (dielectrics for capacitors, actuators) since they are environmentally friendly.
Physica Status Solidi (a) | 2001
F. Bahri; Annie Simon; Hamadi Khemakhem; J. Ravez
Crystallographic and low frequency dielectric studies were performed on lead-tree non-stoichiometric perovskite ceramics of Ba 1-x Bi 2x/3 □ x/3 TiO 3 (0 ≤ x ≤ 0.15) composition. A classical ferroelectric behaviour was shown for x lower than 0.09. A relaxor behaviour appears for higher values of x (0.09 ≤ x < 0.15). The corresponding relaxor characteristics increased as the composition deviated from BaTiO 3 . Such kind of materials are of interest for environmental-friendly applications, in particular the ceramic with composition corresponding to x = 0.15, whose maximum of permittivity occurs at 280 K. i.e. close to room temperature.
Solid State Sciences | 2003
F. Bahri; Hamadi Khemakhem; Annie Simon; R. Von Der Muhll; J. Ravez
Low frequency dielectric studies in the temperature range 80–500 K were performed on the solid solution derived from BaTiO3, Ba1−3aBi2aTiO3 with 0<a<0.117. The temperature and frequency variations of the real part of the relative permittivity show two different behaviors, depending upon the substitution rate. A classical ferroelectric behavior was observed for a varying approximately from 0 to 0.03. However, a relaxor behavior appears for higher values of a. The replacement of Ba2+ by Bi3+ in the A site shows a remarkable decrease of TC. The dielectric studies were confirmed by pyroelectric study.
Solid State Sciences | 2000
J. Ravez; Annie Simon
Abstract Crystallographic and low frequency dielectric studies were performed on new lead-free ceramics derived from BaTiO 3 by cationic substitutions in the 12 C.N. crystallographic site and having the composition Ba 1− x K x /2 La x /2 TiO 3 or Ba 1− x A 2 x /3 TiO 3 (A=La, Bi). A classical ferroelectric behaviour was shown for compositions close to BaTiO 3 , while a relaxor one occured when the composition deviated from BaTiO 3 . In any case, the value of T C (or T m ) and the relaxor characteristics are higher as x increases. Concerning potassium-free ceramics, bismuth compositions compared with lanthanum ones favoured both high ferroelectric and relaxor characteristics due to the lone pair of Bi 3+ . Such new materials are of interest for environmental friendly applications.
Solid State Sciences | 2003
Annie Simon; J. Ravez
Abstract The present work concerns the preparation and dielectric characterization of some new non-stoichiometric lead-free ceramics with perovskite compositions derived from BaTiO 3 . Lead-free compositions could be of great interest for environment-friendly applications (dielectric for capacitors, actuators, etc.). These materials have been shown to be either classical or relaxor ferroelectrics. In the first part of this article, the BaTiO 3 Ba 0.5 NbO 3 system concerns the cationic non-stoichiometry occurring only in the 12-coordination crystallographic site. In the second part, the influence of non-stoichiometry also occurring in the anionic site was determined in compositions belonging to the ternary system 2BaOTiO 2 Nb 2 O 5 . The variation in the Curie temperature T C or the temperature T m of the maximum of e ′ r decreased when the composition deviated from BaTiO 3 and when the number of vacancies increased. On the contrary, the relaxor state was favored by such a deviation.
Solid State Sciences | 2003
F. Bahri; Hamadi Khemakhem; M. Gargouri; Annie Simon; R. Von Der Muhll; J. Ravez
In order to elucidate the correlation between the relaxor type of phase transition and the percent of the A and B site substitution in the Ba1−xNaxTi1−xNbxO3 solid solution, the dielectric permittivity was carried out in the temperature range 80–600 K. All ceramics of these solid solutions present a ferroelectric–paraelectric phase transition with relaxor and classical character depending on the value of x. With increasing x the three phase transition of pure BaTiO3 are pinched into one rounded dielectric peak, and there is evidence for Vogel–Fulcher type relaxational freezing. Raman spectra of the x=0.3 and x=0.7 compositions taken at various temperatures and measured over the wavenumber range 100–1200 cm−1 confirm that the first order scattering is dominant in phonon bands resulting from both ordered region and disordered matrix.
Materials Letters | 2000
A Kerfah; K Taı̈bi; A Guehria-Laı̈doudi; Annie Simon; J. Ravez
Abstract New dielectric oxyfluoride ceramics have been obtained in the ternary system BaTiO 3 BaZrO 3 BaLiF 3 . X-ray powder diffraction studies allowed to determine the limits of solid solutions. Dielectric measurements were performed in the frequency and temperature range 10 2 –2×10 5 Hz and 77–450 K, respectively. This ternary system shows both classical ferroelectric and relaxor ferroelectric behaviours depending on the composition. These results are related to ionic substitution and chemical bonding. In addition, a spontaneous classical ferroelectric–relaxor ferroelectric transition is evidenced for the first time in a lead-free perovskite-type phase. These compositions are of interest for applications (dielectrics for capacitors, actuators) since they are environment-friendly.
Comptes Rendus Chimie | 2002
J. Ravez; Annie Simon
Abstract Preparation and dielectric characterisations of a great number of TTB-type ceramics have allowed us to show that some of them present relaxor behaviour, due to the occupation of the same crystallographic site by two different cations or anions. One of the cation in the octahedral site has to be ferroelectrically active. The relaxor effect is correlated to either cationic distribution disorder in the same site or dilution of the ferroelectric character.
Solid State Sciences | 2002
Hanan El Alaoui Belghiti; Annie Simon; P. Gravereau; Antoine Villesuzanne; Mohamed Elaatmani; J. Ravez
Abstract The Sr2−xK1+xNb5O15−xFx (0⩽x⩽1) solid solution of tetragonal tungsten bronze (TTB)-type was characterized by both crystallographic and dielectric properties. For small values of x (0⩽x