Structural,microstructural and dielectric characterizations of(Bi_(0.5)Na_(0.5))TiO_(3) based lead-free ferroelectric ceramics

(1-x)(Bi_(0.5)Na_(0.5))TiO_(3)-xBaTiO_(3) lead-free ceramics have been obtained from the conventional solid-state reaction sintering method.The structural properties were investigated from X-ray diffraction and Raman spectroscopy techniques.Results revealed well-crystallized ceramic samples with perovskite structure.Microstructural properties,obtained from scanning electron microscopy measurements,have shown high density with very low porosity level.The dielectric response,analyzed as a function of the temperature and several frequencies,showed very broad peaks with a strong frequency dependence of the temperature for the maximum dielectric permittivity for the modified system.Results were analyzed considering the influence of the BaTiO3 content on the studied physical properties.

Relaxor ferroelectric behavior:An approach considering both the dipolar and electrical conductivity contributions

The relaxor behavior of PLZT ferroelectric ceramics has been analyzed in a wide frequency and temperature ranges,below and above the temperature for the formation of the so-called polar nano-regions(PNRs).An approximation to the dynamical behavior of the PNRs has been discussed using Cole-Cole’s relaxation model and Jonscher’s Universal Relaxation Law.The analysis considers both the dipolar contribution and those ones associated with DC and AC electric conductivities,this latter not being previously reported in the literature for relaxor materials.The effectiveness of the developed model has been verified from the agreement between the experimental data and the theoretical calculations.This study also offers an indirect method to predict the DC component of the electrical conductivity.

Electrocaloric effect and freezing temperature in(Pb_(0.8)Ba_(0.2))[(Zn_(1/3)Nb_(2/3))_(0.7)Ti_(0.3)]O_(3) relaxor ferroelectric ceramic

The electrocaloric effect(ECE)is studied in(Pb_(0.8)Ba_(0.2))[(Zn_(1/3)Nb_(2/3))_(0.7)Ti_(0.3)]O_(3) relaxor ferroelectric ceramic by using an“indirect method”.The electric dependence for the polarization(hysteresis loops)has been obtained for several temperatures showing typical relaxor characteristics.The temperature change△T,which is associated with the ECE,is calculated by using the temperature dependence for the polarization.A maximum value for△T is observed for temperatures close above the freezing temperature,showing an indirect evidence of that critical temperature.The results are discussed considering the contribution of the polar nanoregions to the polarization.

Incorporation of dysprosium ions into PbTiO_(3) ferroelectric ceramic system

A structural analysis concerning the incorporation of dysprosium into A-and/or B-sites of the lead titanate is shown.The two"boundary"refinements are presented,i.e.,Dy^(2+)substitutes for Pb^(2+)(Dy^(3+)substitutes for Ti^(4+))and Dy^(3+)substitutes for Pb^(2+)(Dy^(3+)substitutes for Ti^(4+)).The results offer quantitative information about the incorporation into both crystallographic sites.The increase of Dy^(3+)fraction into B-site provides the increase of the Ti^(4+)atomic displacement along the[001]direction and the tetragonal distortion.

Ferroelectric ceramic materials of the Aurivillius family

Ferroelectric ceramics are important materials with a wide range of industrial and commercial applications.Since the discovery of the phenomenon of ferroelectricity,they have been the heart and soul of several multibillion dollar industries,ranging from highdielectric-permittivity capacitors to developments in piezoelectric transducers,pyroelectric sensors,medical diagnostic transducers,electro-optical devices,etc.Materials based on barium titanate and lead zirconate titanate have dominated the field throughout their history.Actually,the ferroelectric ceramics from the Aurivillius family receive great attention due to their large remanent polarization,lead-free nature,relatively low processing temperatures,high Curie temperatures and excellent piezoelectric properties,which made them good candidates for multiple applications.This review presents a general overview of the progress in the studies on the ferroelectric ceramics from the Aurivillius family.The progress includes several aspects:(i)structural studies,(ii)dielectric and electric behavior,(iii)piezoelectricity,and(iv)pyroelectricity.