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The effect of grain size was not fully explored in composites containing ferroelectric and magnetic phases including the independent properties of each phase. Aiming to study the dependence of ferroic and multiferroic properties with average grain size in composites this work reports preparation method and electric, magnetic and magnetoelectric properties of particulate composites with distinct combination of grain size of each phase. A new sintering method was applied to prepare a group of samples with distinct configuration of grain size distribution. With this method it was possible to densify ceramics avoiding grain growth using spark plasma sintering. It was observed that the all ferroic and multiferroic properties were correlated with the setup of grain size of each phase in the composite, by example the dependence of magnetic properties with the electric phase grain size. Besides it was noticed that is possible to improve magnetoelectric coefficient by changing grain size of both phase, even inducing the self-biased effect by decreasing the grain size of the ferroelectric phase.

The monophasic polycrystalline ceramic perovskite-based Eu2Bi2Fe4O12 was synthesized by the solid-state reaction method. X-ray diffraction measurements in the Bragg–Brentano geometry and Rietveld analysis reveal that this material crystallizes in an orthorhombic structure with Pnma (#62) space group. Average grain size of 450 nm is calculated of a log-normal distribution and obtained by means scanning electron microscopy images. Results from magnetization, pyroelectric and complex impedance measurements as a function of temperature (50 K up to 300 K) show the occurrence of dielectric and magnetic relaxation process starting simultaneously at 112.8 K. The tendency of real and imaginary curves of the dielectric permittivity at temperatures close to room temperature has also shown strong ac conductivity contributions attributed to porosity effects. The magnetization hysteresis loop at room temperature confirms that this new perovskite-based material has a ferromagnetic response. Signature of superparamagnetism effects is also observed as a consequence of the nanometric grain size. Thermostimulated current measurements as a function of temperature reveal the occurrence of ferroelectric polarization for the temperature regime below T = 112.8 K. Diffuse reflectance experiments permitted to establish the semiconductor nature of this material at room temperature with an energy gap of 2.65 eV.

In this paper, a quantification of the polar/non-polar phases of perovskite single-phase relaxor ferroelectric ceramics of lanthanum modified lead titanate zirconate (PLZT x/65/35, x = 5, 8, 9 and 10%) was performed by Rietveld refinement using measurements obtained with Cu kα radiation and with high-resolution synchrotron radiation. The refinements were performed concerning two crystalline phases, being one of them nonpolar (Pm-3m) and the other polar. The refinement results showed the relationship between the polar/nonpolar phases and the La content in PLZT, suggesting the existence of polar clusters of relaxor ferroelectric ceramics.

This work uses the electromechanical resonance technique to investigate the piezoelectric properties of Pb0.55Ca0.45TiO3 ceramics as a function of temperature. The elastic compliance coefficient, s11E, and the transverse electromechanical coupling factor, k31, were calculated based on the harmonic oscillator model of piezoelectric vibrating sample. In addition to the analysis of the temperature dependence of the piezoelectric response, the thermal depoling current and the real and imaginary parts of the dielectric permittivity as a function of the temperature were investigated. The thermal stability of the piezoelectric response was determined and the non-accordance of the temperature anomalies of k31, s11E, dielectric and pyroelectric coefficients were discussed.

This paper reports the electric, magnetic and magnetoelectric properties of particulate composites of the system with ferroelectric phase 0.675[Pb(Mg1/3Nb2/3)O3]−0.325[PbTiO3] and magnetic phase CoFe2O4 prepared by Spark Plasma Sintering technique. Optimized sintering and thermal annealing parameters were applied in order to achieve highly dense microstructure with sub micrometric grain size distribution for both phases. The results from the dielectric measurements showed a diffuse and dispersive phase transition. P-E and M-H loops revealed the simultaneous existence of ferroelectric and ferrimagnetic ordering, respectively. Moreover, at cryogenic temperatures an anomalous behavior on the bias magnetic field dependence was observed for the magnetoelectric voltage coefficient.

In this work, the relationship between dielectric, ferroelectric, piezoelectric properties and the magnetoelectric coupling in (1-x)PMN-PT/xCFO multiferroic particulate composites were investigated. The magnetodielectric response showed strong frequency and CFO concentration dependence, which for composites with CFO concentration higher than 30 M%, it was reported a magnetodielectric response up to 10% around the electromechanical resonance regime for magnetic fields of 15 kOe. Additionally, at low magnetic fields a positive magnetodielectric coefficient (∼2%) associated to the magnetoelectric coupling was observed. The MD effects for particulate composites were attributed to the co-contribution of the magnetoelectric polarization, at low magnetic fields, and a compressive stress on ferroelectric phase due to magnetostriction effect, at high magnetic field.

The thermal evolution of the electric field-induced birefringence, δ(Δn(E)) vs T, obtained by the Kerr and Pockels electro-optical effects, was characterized in the La-doped Pb(Mg1/3Nb2/3)O3 – PbTiO3 ferroelectric relaxor ceramic system. The measurements were conducted over a broad temperature range (from 100 K to 650 K), using the dynamic Senarmont compensator method. Moreover, through a particular approach to the analysis of both electro-optical effects as a function of temperature, it was possible to determine the characteristic temperatures predicted for the transitions between the paraelectric (PE), ergodic ferroelectric relaxor (EFR), nonergodic ferroelectric relaxor (NEFR), and normal ferroelectric (FE) states of this system.

Pyroelectric current and magnetoelectric coupling measurements on polycrystalline samples of the quadruple perovskite (LaMn$_{3}$)Mn$_{4}$O$_{12}$ give evidence of ferroelectricity driven by the antiferromagnetic ordering of the $B$-site Mn$^{3+}$ ions at $T_{N,B}$=78 K with record values of remnant electric polarization up to $P$=0.56 $\mu$C cm$^{-2}$. X-ray diffraction measurements indicates an anomalous behavior of the monoclinic $\beta$ angle at $T_{N,B}$, which suggests that $P$ lies in the $ac$-plane, where the moments are collinear, so we conclude that exchange striction is the mechanism of spin-driven ferroelectricity. Polarization values $\sim$3 $\mu$C cm$^{-2}$ are expected in single crystals, which would open the avenue towards practical multiferroic applications., Comment: 5 pages, 5 figures

Transparent relaxor ferroelectric ceramics of the system lanthanum modified lead magnesium niobate have been investigated for a variety of electro-optic properties could make these materials alternatives to (Pb,La)(Zr,Ti)O3. However, a study that relates the properties in function stoichiometric formula, it has not been analyzed heretofore. Therefore, in this work the effect of A-site substitution of La+3 in the characterization microstructural, structural, optical and electro-optical on (1-x)[Pb(1-3/2y)Lay(Mg1/3Nb2/3)O3]-xPbTiO3 and (1-z)[(1-x)Pb(Mg1/3Nb2/3)O3+xPbTiO3]+zLa2O3 has been performed. It was observed that the properties according to the stoichiometric formula and the PT had a maximum whose behavior was related to the addition of lanthanum in each stoichiometries.