F. L. Zabotto

Characterization of La-Doped PBN Ferroelectric Ceramics

In this work, pure and La3+-doped PBN56 ceramics (La3+ added from 0 wt% to 4 wt%) were fabricated and studied concerning its structure, microstructure and dielectric properties. The analysis of the microstructure of the ceramics showed a change of the grain morphology for ceramics with La content higher than 1.0 wt%. X-ray diffraction and Raman spectroscopy were performed to study the structure of the PBN56 ceramics. The results showed the presence of an orthorhombic phase, whose concentration is increased with the increasing of the La3+ content. The analysis of the results was performed to investigate the presence of the orthorhombic phase and the composition where its formation begins.

Dynamics of normal to diffuse and relaxor phase transition in lead metaniobate-based ferroelectric ceramics

Tetragonal tungsten bronze-structured materials based on lead metaniobate (PbNb2O6) were studied in terms of thermal dynamics of dielectric properties, showing ferroelectric-to-paraelectric phase transition of diffuse and relaxor type in some specific cases. These features are normally ascribed to defects-induced structural disorder and compositional fluctuations associated with an arbitrary lattice site occupation between dopant and host ions. Nevertheless, for these lead metaniobate-based materials, the drastic change in the phase transition from normal to diffuse and relaxor is shown to take place when dopants are able to significantly shift the transition toward low temperatures, where these compounds are known to exhibit incommensurate superstructures that naturally present diffuse and relaxor dielectric characteristics.

Effect of Ferrite Concentration on Dielectric and Magnetoelectric Properties in (1-x)Pb(Mg1/3Nb2/3)0.68Ti0.32O3 +(x) CoFe2O4 Particulate Composites

In this work the effect of ferrite concentration on dielectric and magnetoelectric properties in (1-x)Pb(Mg1/3Nb2/3)0.68Ti0.32O3 +(x) CoFe2O4, 0.10 ≤ x ≤ 0.50, particulate composites sintered by conventional method was investigated. Optimized sintering conditions, which resulted in samples with relatively high density and resistivity values, allowed an effective poling processing. Moreover, resulting low phase interdiffusion guaranteed a good 0-3 connectivity maintenance for all compositions. Such sample features allowed to verify that the magnetoelectric coefficient increases as a function of the ferrite content as theoretically expected, reaching a maximum of 30 mV/cmOe for 50 molar% of ferrite phase).

Stress magnetization model for magnetostriction in multiferroic composite

An alternative to obtain multiferroic materials is the production of composite materials that combine ferroelectric and magnetic materials. In particular, the use of magnetostrictive materials as ferromagnetic phase in composites is very important because the mechanical stress applied in ferroelectric phase induces the appearance of magnetoelectric effect. In this work, we have proposed a generalized model for the magnetostriction dependence with the magnetization of the 0-3 type composite magnetoelectric materials. Including both piezomagnetic and stress dependence in the magnetostriction, a relevant improvement was reached as compared to the ordinary square magnetization model. Based on the Gibbs free energy expansion, the magnetostriction behavior of the composite (1−x)Pb(Mg1/3Nb2/3)−xPbTiO3/CoFe2O4 at 300 K and 5 K is described. Furthermore, using the piezomagnetic correction, the magnetostriction data for the pure CoFe2O4 is fitted showing that this ferrite presents a relevant piezomagnetic effect.

Angular Dependence of the Magnetoelectric Effect on PMN-PT/CFO Particulate Composites

In this work the angular dependence of the magnetoelectric response in PMN-PT/CFO particulate magnetoelectric composites was investigated. Magnetostrictive and magnetoelectric measurements were performed as a function of the angle between electric polarization and magnetic bias field for 0–3 particulate ceramic composites prepared through solid state reaction and hot uniaxial pressing methods. The magnetoelectric response showed a strong angular dependence, which can be directly related to the magnetostrictive and piezoelectric properties of composites.

Understanding the dynamic magnetization process for the magnetoelectric effect in multiferroic composites

Based on a magnetic relaxation model, an approach that includes the spin dynamics is proposed and applied to describe the magnetoelectric (ME) effect frequency dependence for a 0–3 type composite at low temperatures. Our results show that the ME coefficient, in low temperatures, for PMN-PT/CFO ( (1−x)Pb(Mg1/3Nb2/3)−xPbTiO3/CoFe2O4) composite has a step-like behavior on the hysteresis loop for frequency of 1 kHz, contrasting with the results at low frequencies (10 Hz). This approach assumes that the ferromagnetic and ferroelectric phases are coupled through the interactions of the spins of the ferromagnetic phase with the composite phonons by spin/lattice relaxation.

Relationship between the ferromagnetic phase and the magnetoelectric coupling in hot pressed Pb(Mg1/3Nb2/3)O3-PbTiO3 based particulate composites

ABSTRACT The influence of ferromagnetic phase properties on the magnetoelectric response of hot pressed particulate composites formed by 80 mol% of 0.675[Pb(Mg1/3Nb2/3)O3]–0.325[PbTiO3] as piezoelectric matrix and 20 mol% of NiFe2O4, CoFe2O4 or BaFe12O19 phases was analyzed. The hot pressing sintering method was suitable for obtaining composites with apparent density higher than 94% and electric resistivity close to 109 Ω.m, independently of the ferromagnetic phases used. The magnitude of the magnetoelectric coupling seems to be governed by the piezoelectric properties of ferroelectric PMN-PT matrix, and the zero bias magnetoelectric coefficient values are determined by the ferromagnetic hardness of the magnetic phase.

Effect of different ferroelectric phases on magnetoelectric properties of Co-ferrite particulate composites

ABSTRACT In this work, the influence of the ferroelectric phase on the magnetoelectric response of particulate magnetoelectric composites were investigated. The composites constituted by PMN-PT, PZT and PBN as ferroelectric phase and CoFe2O4 as ferromagnetic phase (prepared through the conventional solid state method) were synthesized by hot forging method in the 80/20 molar ratio using the 0-3 connectivity. We show that the increase in the magnetic coercive field for composites composed by PZT and PBN in comparison to the PMN–PT ferroelectric phase is related to the different elastic constants of ferroelectric matrix used. Also, the ME properties has been attributed to the mechanically mediated effect, in which the ME values are strongly dependent to the piezoelectric and elastic properties of the ferroelectric phases and the maximization of ME coefficient was obtained using ferroelectric and ferromagnetic phases with similar elastic modulus.

La3+-induced (micro)structural changes and origin of the relaxor-like phase transition in ferroelectric lead barium niobate electroceramics

Lead barium niobate (Pb1−xBaxNb2O6, PBN) ferroelectric materials have been and are the subject of numerous studies in literature due to their potential for wide-ranging applications in the electronic industry. In this work, La3+-doped Pb0.56Ba0.44Nb2O6 (PBN44) electroceramics were prepared and investigated in terms of X-ray diffraction, scanning electron microscopy, thermal spectra of dielectric permittivity, Curie–Weiss law, and hysteresis loop characteristics. It was noted that La3+ doping favors the formation of orthorhombic mm2 phase in PBN44, which originally shows only the tetragonal 4mm symmetry-related phase. In particular, the PBN44 material with 1 wt% La2O3 displays (micro)structural characteristics and dielectric properties similar to those from PBN compositions lying within their morphotropic phase boundary region. Our results also show that La3+ is able to promote a change of the ferroelectric to paraelectric phase transition appearance of PBN44 from pseudo-normal to really diffuse. However, conversion to a diffuse plus relaxor transition behavior reveals directly linked to incommensurate superstructures present and dielectrically-active in PBN materials toward low temperatures, with an intrinsically frequency-dispersive dielectric response. This statement is also supported by observation of hysteresis loops showing a transformation trend to pseudo-slim-like, even in the normal-like ferroelectrics, when moving into the temperature region of incommensuration manifestation.

Influence of Densification Method on Microstructural, Electric and Magnetoelectric Properties of the PMN-PT/NFO Composites

In this work the influence of the densification method on microstructure, electric and magnetoelectric properties of the (1-x) [0.675Pb(Mg1/3Nb2/3)O3-0.325PbTiO2] + xNiFe2O4 (PMN-PT + NFO) particulate composites, for 0.15 ≤ x ≤ 0.30 molar percent, was systematically analyzed. Conventional sintering and hot pressing as sintering methods were used. The hot pressing method affords an enhancement of the microstructural and electric properties of composites, in which samples with apparent density values close to 99% and electric resistivity larger than 107 Ω.m were obtained. On the other hand, the increase of the grain size occurring with conventional sintering affords higher ME coefficients (∼12 mV/cm.Oe). In addition, the magnetic field at which the ME is maximum increases with NFO amount, indicating a tuning of the maximum ME effect by choice of ferrite concentration.