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.

Switching and energy-storage characteristics in PLZT 2/95/5 antiferroelectric ceramic system

Switching mechanisms and energy-storage properties have been investigated in(Pb_(0.98)La_(0.02)T(Zr_(0.95)Ti_(0.05)T_(0.995O_(3)) antiferroelectric ceramics.The electric field dependence of polarization(P–E hysteresis loops)indicates that both the ferroelectric(FE)and antiferroelectric(AFE)phases coexist,being the AFE more stable above 100℃.It has been observed that the temperature has an important influence on the switching parameters.On the other hand,the energy-storage density,which has been calculated from the P–E hysteresis loops,shows values higher than 1 J/cm^(3) for temperatures above 100℃ with around 73%of efficiency as average.These properties indicate that the studied ceramic system reveals as a promising AFE material for energy-storage devices application.

Exploring the electromechanical response and electric field-induced dielectric anomalies in PMN-PT electroceramics

Electromechanical and dielectric properties of PMN-PT ferroelectric ceramics are investigated.In particular,dielectric response studies focus on the investigation of the influence of the DC applied electric field on the dielectric permittivity as a function of temperature and frequency.Results reveal an electric field driven dielectric anomaly in the dielectric permittivity curves,e(E),which in turn prevails in the whole ferroelectric phase region and continuously vanishes for temperatures near the paraelectric-ferroelectric phase transition temperature.A schematic model for the domains dynamics of the studied material is proposed taking into account the simultaneous contribution of both 90°and 180°domains walls.

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.

Debye's temperature and heat capacity for Sr_(0.15)Ba_(0.85)Bi_(2)Nb_(2)O_(9) relaxor ferroelectric ceramic

A lead-free relaxor ferroelectric,Sr_(0.15)Ba_(0.85)Bi_(2)Nb_(2)O_(9),was synthesized via solid-state reaction and the temperature-dependence of the heat capacity was measured in a wide temperature range.The dielectric permittivity was also measured between 500 Hz and 5 MHz in the same temperature range.No anomaly has been detected in the heat capacity curve for the whole temperature range covered in the present experiments,while broad peaks have been observed in the dielectric permittivity with high frequency dispersion.A typical relaxor behavior has been observed from the dielectric analysis.The Debye's temperature has showed a minimum value near the freezing temperature.The results are discussed considering the spin-glass model and the high frequency dispersion,which has been observed for the studied relaxor system.

EVIDENCES OF A STRUCTURAL PHASE TRANSITION IN THE NEW Pb(Zr_(y)Ti_(1-y))O_(3)MODIFIED TELLURITE GLASS-CERAMIC COMPOSITE

The physical properties of the new TeO_(2)-B_(2)O_(3)-PbO_(2)(TBP)-based glass system,obtained from the usual melt-quench method,have been investigated taking into account the infuence of the Pb(Zr_(y)Ti_(1-y))O_(3)(PZT)ferroelectric system.A crystalline-like structure,which characterizes a glass-ceramic-like state,promoted by the ferroelectric phase,has been revealed from the X-ray diffraction results for the sample with higher PZT concentration.On the other hand,results on the dielectric response revealed noticeable dielectric anomalies,which until now have not been reported.In fact,the dielectric and ferroelectric properties suggest the existence of a structural phase transition induced by the PZT crystalline phase,which indeed have been related to the ferroelectric polar-phase regions embedded into the glass matrix.