Manuel Lente

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Papers by Manuel Lente

Invertigation of field-induced piezoelectric properties in Pb(MgNb)O-PbTiO ceramics for transducer applications

Key Engineering Materials

Non-linear dielectric properties in based-PMN relaxor ferroelectrics

Journal of the European Ceramic Society, 2007

The investigation of the non-linear dielectric response in ferroelectric materials has become one... more The investigation of the non-linear dielectric response in ferroelectric materials has become one of the most important issues in the field of ferroelectricity due to its technological and scientific interest. Rather, from the practical point of view the understanding of the non-linear dielectric properties is essential to improve the performance of ferroelectric multilayer capacitors and actuators devices, which commonly operate at high field levels. On the other hand, the non-linear (NL) dielectric response to large electric fields has been revealed as a powerful technique to investigate the physical origin of the dielectric relaxor state. In this work, low frequency dielectric measurements were performed in 0.9[Pb(Mg1/3Nb3/2)O3]–0.1PbTiO3 (PMN–PT) relaxor ceramics in a wide frequency and temperature range. The non-linear dielectric properties were investigated by using the measurements of the dielectric permittivity of the PMN–PT as a function of the dc “bias” driving field. The obtained results were analyzed within the framework of the current models for the dielectric response of relaxor ferroelectrics.

Magnetoelectric Contribution to Magnetoelastic Coupling in Pb(Fe1/2Nb1/2)O3 Multiferroics Ceramics

Integrated Ferroelectrics, 2011

ABSTRACT In this work, electrical permittivity, magnetic and anelastic measurements in lead iron ... more ABSTRACT In this work, electrical permittivity, magnetic and anelastic measurements in lead iron niobate ceramics (PFN) were performed in the frequency and temperature range from 1 kHz to 10 MHz and from 15 K to 400 K, respectively. Anelastic results characterized unambiguously the magnetoelectric effect in the PFN, demonstrating that ME coupling arises indirectly via strain contribution rather than a direct coupling between electrical and magnetic order parameters.

Ferroelectric Domain Dynamics in PMN-PT Ceramics

Ferroelectrics, 2003

ABSTRACT The polarization switching process was investigated in PMN-PT ceramics through the frequ... more ABSTRACT The polarization switching process was investigated in PMN-PT ceramics through the frequency dependence of the hysteresis loops and the electric field induced-strain measurements. In order to investigate the influence of the ferroelectric phase on the domain reorientation process, PMN-PT ceramics with rhombohedral and tetragonal symmetries were studied. The higher coercive field observed in the tetragonal composition was associated with a higher lattice distortion. The results suggested that the ceramic with rhombohedral symmetry presents a higher collective reorientation of the domains than the tetragonal one. The reorientation of the domains was modeled as occurring in a viscous medium where several resistance forces such as viscous force and restoring forces act on them. The coercive field was interpreted as an effective field necessary to overcome these resistance forces.

Phase transitions and magnetoelectroelastic instabilities in Pb(Fe1/2Nb1/2)O3 multiferroic ceramics

Acta Materialia, 2013

Sintering of layered ferrite-BaTiO3 ceramics: Analysis of interfaces and effects of shrinkage mismatch

Processing and Application of Ceramics

In the present work, densification and microstructure evolution of cobalt ferrite (FCO), nickel-c... more In the present work, densification and microstructure evolution of cobalt ferrite (FCO), nickel-cobalt ferrite (FNICO) and BaTiO3 (TB) ceramics under different sintering conditions were investigated. Subsequently, layered ferrite-BaTiO3 samples were formed by uniaxial pressing of the corresponding ceramic powders. These green samples were sintered with two different sintering schedules, aiming to study the ferrite-BaTiO3 interfaces after sintering. The analyses were made at the cross section of the interfaces and at the interface surfaces after separation of the layers. The sintered layered samples were utilized to analyze sintering mismatch, diffusion at the interfaces and identification of some newly formed phases. EDS analysis across the TB-FCO interface showed evidences of diffusion. It was observed that the FNICO layers were detached from TB during sintering, but the same was not observed in the TB-FCO samples, although shrinkage mismatch resulted in some defects. XRD analyses ...

The use of pulsed electric acoustic technique for measuring electric field profiles in ferroelectric ceramic

Proceedings. 11th International Symposium on Electrets

The pulsed electric acoustic technique, PEA, have been usually applied to probe space charge prof... more The pulsed electric acoustic technique, PEA, have been usually applied to probe space charge profiles in polymers. In this work we show preliminary results obtained with lead zirconate-titanate and niobium, PZTN, ferroelectric ceramic samples. Experiments showed that induced charge densities on sample electrodes are mainly due to the ferroelectric polarization of the sample. We present results of the typical PEA

Sintering of ferrite-BaTiO3 bulk particulate composites

Ceramics International, 2021

Abstract Particulate magnetoelectric ceramic composites (PMCC) have received much attention since... more Abstract Particulate magnetoelectric ceramic composites (PMCC) have received much attention since the last decade. These composites have many technological applications and are usually composed by magnetostrictive and piezoelectric phases. Cobalt-based spinel ferrites are among the most studied magnetostrictive phases for ferrite-based PMCCs and BaTiO3 is an interesting choice for the piezoelectric phase because it is a lead-free ceramic, unlike the traditional PZT. In this work, cobalt ferrite (FCO) and Ni-Co ferrite (FNICO) were produced by the ceramic method and mixed to BaTiO3 (TB) in order to further obtain sintered ferrite-BaTiO3 particulate ceramic composites with a composition of 15 mol% ferrite – 85 mol% BaTiO3. The ferrites, the BaTiO3, and the ferrite-BaTiO3 mixtures were analyzed by dilatometry, thermogravimetry (TG), and calorimetry (DSC) in temperatures up to 1300-1400 oC, with the aim to analyze the sintering behavior and the interactions between both ferrites and the BaTiO3 during sintering. Sintered TB-FNICO and TB-FCO composite samples were also produced and they were analyzed by scanning electron microscopy (SEM) and X-ray diffractometry (XRD). The dilatometry results evidenced that the densification of the ferrite-BaTiO3 samples is impaired, when compared to the pure ferrite and BaTiO3 samples. The DSC/TG results evidenced the occurrence of reactions between the ferrites and the BaTiO3 when they are co-sintered in air or argon atmospheres. The XRD patterns of the sintered composite samples did not exhibit diffraction peaks attributed to a third phase, whilst the punctual EDS analysis showed evidence of diffusion between the ferrite and BaTiO3 particles.

Octahedral distortion and oxygen vacancies induced band-gap narrowing and enhanced visible light absorption of Co/Fe co-doped Bi3.25Nd0.75Ti3O12 ferroelectrics for photovoltaic applications

Journal of Physics D: Applied Physics, 2020

Bandgap narrowing of Ba0.92Na0.04Bi0.04TiO3 ferroelectric ceramics by transition metals doping for photovoltaic applications

Materials Chemistry and Physics, 2021

Abstract A wide bandgap is one of the greatest issues that restrain the photoelectric application... more Abstract A wide bandgap is one of the greatest issues that restrain the photoelectric application of classical ferroelectric oxides in the visible spectrum. Typical approaches to reduce their bandgap, as well as to tune other physical properties (dielectric, piezoelectric …), is to use specific dopants. This work reports the variation by doping of the structural and optical bandgap properties of the Ba0.92Bi0.04Na0.04Ti0.96M0.04O3 (BNBT-M); (M = Ni, Fe, Co) ceramics. Structural refinement shows that all samples are crystallized with a tetragonal phase with a P4mm space group. Detailed analysis of the bond lengths, bond angles, octahedral distortions demonstrates the cooperative effect induced by the Co, Fe, and Ni doping. UV–Vis absorption spectra showed a decrease in the bandgap and increased absorption for longer wavelengths, induced by transitions metal (TM) ions doping. The bandgap narrowing is attributed to the development of new M − O bonds and states in the electronic structure, as the TM ions are incorporated on the Ti site, with simultaneous oxygen vacancies creation. The formation of oxygen vacancies via metal ions doping in BNBT was proven by ESR study. The present investigation can provide useful insight into the understanding and ferroelectrics bandgap tuning for visible-light photovoltaic applications.

Sintering behavior and electromagnetic properties of a Ni–Co ferrite/NiO biphasic ceramic

Materials Research Express, 2019

The normal to diffuse phase transition crossover from thermal expansion analysis in calcium modified lead titanate

Ferroelectrics, 2018

Local polarization exists in ferroelectric materials with diffuse phase transition even above the... more Local polarization exists in ferroelectric materials with diffuse phase transition even above the temperature at which the dielectric permittivity reaches its maximum (T M). The net polarization only cancels above the so-called Burns temperature (Td). In this work, polarization vs. temperature curves of Pb 1Àx Ca x TiO 3 (PCT) ceramics, with 0.35 x 0.55, were determined from experimental data of thermal expansion, considering strain and polarization relations and assuming that the electrostriction coefficient is constant in the paraelectric state. The Burns temperature was determined and compared to T M for each composition, and the achieved results indicate that a crossover from normal to diffuse phase transition occurs at x$0.475.

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Prospection of (Pb,Ca)TiO<inf>3</inf> morphotropic phase boundary from experimental thermal analysis data

2016 Joint IEEE International Symposium on the Applications of Ferroelectrics, European Conference on Application of Polar Dielectrics, and Piezoelectric Force Microscopy Workshop (ISAF/ECAPD/PFM), 2016

Thermal expansion features of the (1-x)PbTiO3-xCaTiO3 (PCT) ceramics were experimentally investig... more Thermal expansion features of the (1-x)PbTiO3-xCaTiO3 (PCT) ceramics were experimentally investigated in a wide temperature range (150-900K). Distinct anomalies of the thermal expansion coefficient were observed in all compositions. Typical negative thermal expansion behavior of the displacive ferroelectric lead titanate system still remained for calcium concentrations up to ~42.5mol%. Additionally, the temperatures of nonpolar-nonpolar, nonpolar-polar and polar-polar phase transitions were found to be in agreement with those expected for a morphotropic phase boundary region earlier proposed in the literature for the PCT system.

Respuesta no lineal en láminas delgadas ferroeléctricas

Phase diagram of the relaxor (1−x)Pb(Zn1/3Nb2/3)O3–xPbTiO3 investigated by dielectric and Raman spectroscopies

Solid State Communications, 2004

ABSTRACT Lead zinc niobate–lead titanate[(1−x)Pb(Zn1/3Nb2/3)O3–xPbTiO3] (PZN–PT) crystals with x=... more ABSTRACT Lead zinc niobate–lead titanate[(1−x)Pb(Zn1/3Nb2/3)O3–xPbTiO3] (PZN–PT) crystals with x=4.5% and x=12% have been investigated using dielectric and Raman measurements over a range of temperatures. Above room temperature, dielectric measurements show that both compositions exhibit structural phase transitions according to the phase diagram proposed by Kuwata et al. [Ferroelectrics 387 (1981) 579]. Below room temperature, an anomaly at around 180 K for the x=12% sample is observed, suggesting another phase transition. Raman measurements are used to study all phase transitions.

Influence of Complex Defects on the Domain Switching Dynamics in Ferroelectric Ceramics

ABSTRACT In this work, the influence of the complex defects on the domain switching dynamics in d... more ABSTRACT In this work, the influence of the complex defects on the domain switching dynamics in doped Pb(Zr 0.53 ,Ti 0.47)O 3 bulk ceramics (PZT) was investigated. It was verified that the complex defects, present in the hard PZT, initially reduce the coercive field and increase the percentage of backswitching. Nevertheless, during the continuous polarization switching these defects tend to reorient perpendicularly to the spontaneous polarization of domains, thus, increasing the coercive field and reducing the backswitching. Additionally, the frequency dependence of the coercive field was strongly influenced by the configuration of complex defects into the ferroelectric matrix. RESUMEN En este trabajo fue investigada la influencia de defectos complejos sobre la dinámica de reorientación de dominios en cerámicas de Pb(Zr 0.53 ,Ti 0.47)O 3 modificadas (PZT). Fue verificado que los defectos complejos, presentes en el sistema PZT duro, reduce el campo coercitivo y aumenta el porcentaje de retorno de la polarización. Por otro lado, durante una continua reorientación de la polarización, estos defectos tienden a reorientarse perpendicularmente a la dirección de la polarización espontánea, aumentando así el campo coercitivo y reduciendo el retorno de la polarización. Además, la dependencia del campo coercitivo con la frecuencia fue influenciada por la configuración de los defectos complejos dentro de la matriz ferroeléctrica.

The process of polarization in PZT ceramics

ABSTRACT Neste trabalho o processo de reorientação dos domínios durante a polarização foi investi... more ABSTRACT Neste trabalho o processo de reorientação dos domínios durante a polarização foi investigado em cerâmicas de PZT &quot;puras&quot; e dopadas com Nb2O5 ou Fe2O3 a partir de medidas do transiente de corrente elétrica e histerese ferroelétrica. Os resultados experimentais possibilitaram identificar os mecanismos responsáveis para a polarização e suas contribuições para a polarização total. A relaxação da polarização após a remoção do campo elétrico c.c. foi calculada e comparada com os resultados de envelhecimento destas cerâmicas. O processo de reorientação dos domínios mostrou ser altamente influenciado pela presença de impurezas.

PLZT and PLMN-PT transparent ferroelectric ceramics: processing and properties

ABSTRACT Transparent ferroelectric ceramics have been extensively employed in optical and electro... more ABSTRACT Transparent ferroelectric ceramics have been extensively employed in optical and electrooptical devices. The recent progresses achieved by the GCFerr/DF UFSCar in the production of the transparent ferroelectric ceramics, through uniaxial hot-pressing technique, are presented. The physical property characterization, as microstructural, structural, optical, dielectrical, pyroelectric, electro-optical, electrostrictive and ferroelectric are reported for lanthanum modified lead zirconate titanate (PLZT) and lanthanum modified lead magnesium niobate lead titanate (PLMN-PT) ceramics. The results revealed a homogeneous microstructure, high densities and absence of second phases for the ceramics of both compositions. Consequently, high optical transmittance was found in the visible and infrared range. The electrical measurements also presented excellent results when compared to those reported in the literature confirming the high quality of the samples.

O processo de polarização em cerâmicas de PZT

Cerâmica, 2000

Neste trabalho o processo de reorientação dos domínios durante a polarização foi investigado em c... more Neste trabalho o processo de reorientação dos domínios durante a polarização foi investigado em cerâmicas de PZT "puras" e dopadas com Nb2O5 ou Fe2O3 a partir de medidas do transiente de corrente elétrica e histerese ferroelétrica. Os resultados experimentais possibilitaram identificar os mecanismos responsáveis para a polarização e suas contribuições para a polarização total. A relaxação da polarização após a remoção do campo elétrico c.c. foi calculada e comparada com os resultados de envelhecimento destas cerâmicas. O processo de reorientação dos domínios mostrou ser altamente influenciado pela presença de impurezas.

$Research paper thumbnail of Field induced piezoelectric transducer for generation of controlled diffraction ultrasonic field$

Field induced piezoelectric transducer for generation of controlled diffraction ultrasonic field

IEEE Ultrasonics Symposium, 2005.

In this work, ultrasonic transducers were developed using relaxor ferroelectric ceramics based on... more In this work, ultrasonic transducers were developed using relaxor ferroelectric ceramics based on modified-lead magnesium niobate lead titanate ceramics (PMN-PT). It was found that PMN-PT ceramics present large field-induced electromechanical coupling factors, high piezoelectric anisotropy (kt/kp&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;gt;&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;gt;1) and relative high mechanical quality factor at relatively low DC bias field. Thus, &amp;amp;amp;amp;amp;amp;amp;amp;amp;quot;Bessel-like&amp;amp;amp;amp;amp;amp;amp;amp;amp;quot; transducer, which was composed of three concentric electrodes, based on