Magnetoelectric Particulate Composites Research Articles

Microstructural and physical characterizations of (1-x)(0.67BiFeO3+ 0.33BaTiO3+ 1%MnO2)− x(CoFe2O4+ 3%ZnO) magnetoelectric composites

BiFeO3 (BFO) was mixed with BaTiO3 (BTO) to form a solid solution of large piezoelectric coefficient (d33) for the fabrication of magnetoelectric (ME) composites with the Zn-doped CoFeO4 (CFO). The 0.67BFO+0.33BTO solid solution, which was doped with 1 at% MnO2 for lowering leakage current, showed a high d33 of 121 pC/N. However, in the composites made with CFO, a much lower d33 (<42 pC/N) was retained. The microstructure of the composites was featured by the large CFO grains (∼5 μm) embedded in the 0.67BFO+0.33BTO matrix of much finer grains (∼0.5 μm). The CFO grains each had a well-defined morphology with clear boundary discriminating them from the neighboring piezoelectric phase. Both the CFO and piezoelectric grains showed a high crystallinity as indicated by the appearance of clear Kikuchi patterns in electron backscattered diffraction. After reducing DC conductivity of CFO by Zn-doping and the optimization of fractional ratio of the Zn-doped CFO in the composites, a ME voltage coefficient of 81.8 mV/cm-Oe was achieved, which was high among the lead-free particulate ME composites prepared by the conventional solid-state sintering.

Electrical and Magnetoelectric Properties of Particulate Composites and Laminated Trilayered Thick‐Film Composites

Hydraulic pressing and screen printing methods are used to create particulate magnetoelectric composites and laminated trilayered thick‐film composites. X‐ray diffraction studies reveal the presence of cubic spinel and tetragonal perovskite structures for individual powders of ferrite CuFe2O4 and ferroelectric‐phase PbZr0.58Ti0.42O3. The dielectric constant of particulate composites decreases with increasing frequency around 1 MHz and beyond that frequency, a saturation state is attained. However, for laminated films, the dielectric constant decreases up to 1 MHz and then increases. The maximum dielectric constant at low frequency for particulate CuFe2O4/PZT composites is around 72.2, whereas for laminated CuFe2O4/PZT/CuFe2O4 composites it is 4.97 and for PZT/CuFe2O4/PZT composites is 5.24. Loss tangent exhibits the same trend as dielectric constant with frequency, which is explained by space charge polarization and is consistent with Koop's phenomenological theory. The dielectric constant's variation with temperature describes the contribution of electric dipoles to polarization and both composites exhibit absorption peaks. The semiconducting nature of both particulate and laminated composites can be seen in the DC resistivity graph with frequency and as frequency increases, DC resistivity decreases for both composites, which is explained by the small polaron‐hopping phenomenon. The magnetoelectric coupling effect for particulate composites (44 mV Oe−1cm−1) is also found to be small when compared to laminated trilayered composites (CuFe2O4/PZT/CuFe2O4—105 mV Oe−1cm−1 and PZT/CuFe2O4/PZT—68 mV Oe−1cm−1).

Large magnetoelectric effect in BaFe12O19-(Ba0.85Ca0.15)(Zr0.1Ti0.9)O3 particulate composite

Multiferroic composites with a large magnetoelectric response are gaining attractive interests for the design of magnetoelectric (ME) functional devices. In this work, the particulate ME composites (Ba0.85Ca0.15)(Zr0.1Ti0.9)O3–xBaFe12O19 (x=0, 0.1, 0.2, 0.3, 0.4 and 1) were prepared, and their structural, dielectric, magnetic, ferroelectric, piezoelectric properties and magnetoelectric coupling were systematically investigated. The composites consisted of only two chemically separated phases with well-bonded interface. Dielectric and impedance analyses indicated the co-contribution of grain and grain boundary to polarization. Well-saturated ferroelectric and magnetic hysteresis loops demonstrated multiferroic nature. ME response was investigated elaborately by employing magnetically induced polarization, together with measuring ME voltage coefficient and magnetodielectric value. Specifically, a large ME coefficient of 26.78 ​mV/cm·Oe was achieved for x=0.3, which is higher than that in single-phase BaFe12O19 and its coupled composites.

Biphasic 0.8BaTiO3/0.2Ni(1-x)CoxFe2O4 nanopowders by in situ sol-gel synthesis

Nanopowders of the 0.8BaTiO3/0.2Ni(1-x)CoxFe2O4 (x=0, 0.25, 0.5, 0.75, and 1) were synthesized by the in situ sol-gel method using poly(acrylic acid) (PAA1800) as a chelating agent. The synthesis developed using PAA1800 ensured the simultaneous crystallization of two phases. The results provided a reliable method for producing biphasic nanopowders in all the compositions of Co-Ni-ferrite with an average particle size of less than 50 nm with a potential application in lead-free magnetoelectric particulate composites. The XRD results indicated the formation of only BaTiO3 and Ni(1-x)CoxFe2O4 phases, verifying that there was no interdiffusion between the perovskite BaTiO3 and spinel Co-NiFe2O4 phases during the crystallization phase. A detailed analysis of the crystalline structures was conducted to quantify the phases using the Rietveld method, and thus ensure the success of the in situ sol-gel synthesis.

Enhanced magneto-electric properties and magnetodielectric effect in lead-free (1-x)0.94Na0.5Bi0.5TiO3-0.06BaTiO3–x CoFe2O4 particulate composites

The lead-free magnetoelectric particulate composites (1-x)0.94Na0.5Bi0.5TiO3-0.06BaTiO3–x CoFe2O4 (where, x = 0, 0.15, 0.25, 0.35, 0.45) were synthesized by the solid-state sintering technique. The coexistence of piezoelectric 0.94Na0.5Bi0.5TiO3-0.06BaTiO3 (NBBT) and ferromagnetic CoFe2O4 (CFO) phases were confirmed by structural studies. The average crystallite size and the strain produced in the composites between the interface of different phases were estimated using Williamson-Hall method. The microstructural analysis indicates that the closely dense-packed CFO grains are distributed in the NBBT matrix. The ferroelectric nature of the composites was confirmed by the polarization versus electric field hysteresis loop and found to decrease with CFO content, which is attributed to the conducting nature of CFO. The observed values of saturation (Ms), remanent (Mr) magnetization, and magnetic moment (µB) in the composites are 28.46 emu/gm, 5.01 emu/gm and 1.13 µB, respectively for the higher CFO content. The dielectric relaxation phenomena in the composites have been observed, and the enhanced dielectric constant (ε′) is explained based on the electron hopping mechanism. All composites exhibit a relaxor nature which is described by the Vogel–Fulcher relation. The magnetoelectric coupling is estimated in the composites indirectly by measuring the relative change in the dielectric constant in the presence of the external magnetic field. The estimated values of magneto-capacitance at 1 kHz frequency for 25 and 35 mol% are ~ − 5.5 and ~ − 6%, respectively, which indicate that these materials can be useful for magneto-dielectric based devices applications.

On the magnetoelectric performance of multiferroic particulate composite materials

In the current work, quantitative analysis of magnetoelectric particulate composite material system explicated the main mechanisms responsible for the below-optimal performance of this class of materials. We considered compliant particulate composite materials, with constituents relevant to technological and scientific interest, leading to 0–3 Terfenol-D/PVDF–TrFE composite samples. To this objective, thick Terfenol-D/PVDF–TrFE films (10–15 µm) were fabricated and analyzed for chemical, mechanical, and magnetic properties to demonstrate their suitability for energy applications in harsh environmental conditions. The vigorous experimental characterization of the composite exemplified the multifunctional properties, quantifying the interrelationship between the composition and performance. We observed that the addition of magnetic particles to the electroactive copolymer matrix resulted in improvement in the mechanical and electrical properties since the particles acted as pinning sites, hindering the deformation of the chains and enhancing polarization. The effective modulus model was amended to account for the crystallization-induced change in material stiffness. We also measured and computed the magnetic particles motion to explicate the detrimental effect of mobility and migration on the overall magnetoelectric coupling performance of the composite. Thereby, we derived an analytical model based on the magnetic force due to the co-presence of alternating and constant magnetic fields, and the viscous drag force due to the viscoelastic properties of the electroactive copolymer matrix. We demonstrated that the mobility of the particles plays a crucial role in the short and long term performance of magnetoelectric coupling in multiferroic particulate composites, uncovering the underpinnings of the dichotomy in performance between experimentally measured and analytically predicted coupling coefficients, thus allowing for the proposal of new approaches to realize the scientific potential of magnetoelectric particulate composites in energy applications.

Maintenance of integrity between phases in PMN-PT/NFO hot-forged particulate magnetoelectric composites

The influence of hot forging temperature on microstructure and magnetoelectric properties in (0.8)Pb(Mg1/3Nb2/3)0.68Ti0.32O3+(0.2) NiFe2O4 particulate composites were investigated. Samples sintered at intermediate stage of sintering show inter-diffusion and high conductivity resulting in low magnetoelectric coupling related to charge leak current. Composites sintered before the initial stage of sintering show apparent density aprox. 90% and low magnetoelectric coefficient due to poor mechanical coupling between phases. Composites sintered at initial stage of sintering showed improved apparent density (>98%) and resistivity (>108 Ωm). These characteristics allowed an enhancement of magnetoelectric coupling (∼6 mV/cmOe) due to control of inter-diffusion added to enhancement of the microstructural properties.

Simultaneous two-phase formation model in synthesized SBN/NFO using the in-situ modified Pechini method

The main aim of this research was to investigate the in situ co-synthesis of Sr0.61Ba0.39Nb2O6/NiFe2O4 (SBN/NFO) magnetoelectric particulate composites using a modified Pechini method, as well as propose a model to understand the simultaneous formation of two crystalline phases in these materials. Powder samples of SBN/NFO with 50/50, 70/30 and 80/20 M ratios were analyzed using structural analysis techniques, combining both X-ray diffraction and Rietveld structural refinement in orderto identify and quantify the phases in the samples. Based on the results, a phase formation model for the co-synthesis was proposed considering Hume-Rothery rules. This model led us to conclude that the formation of precipitates during the development of the polymeric resin by the modified Pechini method would be the main factor responsible for the presence of spurious phases in the synthesis of SBN/NFO composites. The reduction in the concentration of spurious phases may occur during the polymer resin formation step or when using a different solvent to prevent the formation of precipitates.

Magnetoelectric properties of lead-free (80Bi0.5Na0.5TiO3-20Bi0.5K0.5TiO3)-Ni0.8Zn0.2Fe2O4 particulate composites prepared by in situ sol-gel

Lead-free multiferroic ceramics consisting of (1-x) (80Bi0.5Na0.5TiO3-20Bi0.5K0.5TiO3) (BNT-BKT)-xNi0.8Zn0.2Fe2O4 (NZFO) (x = 0, 0.15, 0.25, 0.35, and 0.45) were synthesized by the in situ sol-gel method. The structural, ferroelectric, piezoelectric, ferromagnetic, and magnetoelectric (ME) properties were measured as a function of the NZFO content x. The results showed that the coexistence of BNT-BKT and NZFO phases and the presence of the morphotropic phase boundary in the BNT-BKT phase with a high piezoelectric coefficient d33 (∼131 pC/N) were confirmed. The composites exhibited a homogeneous microstructure and well-combined interfaces between the magnetostrictive and piezoelectric phases, as well as an improved ME response. The largest ME voltage coefficient (αME) of 42.41 mV/cm Oe was achieved for the 0.65(BNT-BKT)-0.35NZFO composite, which is in fact the highest one reported so far for lead-free particulate ME composites fabricated via in situ processing.

High Curie temperature and enhanced magnetoelectric properties of the laminated Li0.058(Na0.535K0.48)0.942NbO3/Co0.6 Zn0.4Fe1.7Mn0.3O4 composites

Laminated magnetoelectric composites of Li0.058(Na0.535K0.48)0.942NbO3 (LKNN)/Co0.6Zn0.4Fe1.7Mn0.3O4 (CZFM) prepared by the conventional solid-state sintering method were investigated for their dielectric, magnetic, and magnetoelectric properties. The microstructure of the laminated composites indicates that the LKNN phase and CZFM phase can coexist in the composites. Compared with the particulate magnetoelectric composites, the laminated composites have better piezoelectric and magnetoelectric properties due to their higher resistances and lower leakage currents. The magnetoelectric behaviors lie on the relative mass ratio of LKNN phase and CZFM phase. The laminated composites possess a high Curie temperature (TC) of 463 °C, and the largest ME coefficient of 285 mV/cm Oe, which is the highest value for the lead-free bulk ceramic magnetoelectric composites so far.

Enhanced magnetoelectric properties of the laminated Ba0.9Ca0.1Ti0.9Zr0.1O3/Co0.8Ni0.1Zn0.1Fe2O4 composites

Magnetoelectric composite ceramics of Ba0.9Ca0.1Ti0.9Zr0.1O3 (BCZT) with high dielectric constant and Co0.8Ni0.1Zn0.1Fe2O4 (CNZF) with high saturation magnetizations were synthesized via the solid state reaction method. The phase compositions and surface morphology of the composites were investigated using X-ray diffractometer (XRD), Scanning Electronic Microscopy (SEM) and Energy Dispersive Spectrometer (EDS). The dielectric, magnetic, and magnetoelectric properties of the composites were also investigated, and the properties of the composites could be adjusted by the ferrite content. The higher dielectric constant of BCZT/CNZF laminated composites are mainly attributed to the Maxwell-Wagner polarization. Compared with the magnetoelectric particulate composites, the magnetoelectric laminated composites have higher resistivities and lower leakage currents. The largest magnetoelectric coefficient of the laminated composites reaches up to 21.73 mV/cm Oe at 1100 Oe, which is twenty times as large as that of the particulate composites (1.45 mV/cm Oe).

Crossover from ordinary to relaxor ferroelectric state in particulate magnetoelectric composites (x)Mn0.4Zn0.6Fe2O4 – (1-x)PbZr0.53Ti0.47O3

ABSTRACTParticulate magnetoelectric composites (x)Mn0.4Zn0.6Fe2O4 – (1-x)PbZr0.53Ti0.47O3 with x = 0, 0.1, 0.2, 0.3, 0.4, and 0.8 have been prepared using the ceramic technology. Prepared composites with x = 0.2 was revealed to be characterized by the crossover from the ordinary ferroelectric state to the relaxor ferroelectric state, and figure of merits of their magnetoelectric properties for the relaxor ferroelectric state exceed similar values for the ordinary ferroelectric state.

Magneto-electric properties of in-situ prepared xCoFe2O4-(1-x)(Ba0.85Ca0.15)(Zr0.1Ti0.9)O3 particulate composites

Magneto-electricparticulate composites, [xCoFe2O4– (1-x)(Ba0.85Ca0.15)(Zr0.1Ti0.9)O3](x=30, 40, 50wt%), were synthesized in-situ by a modified sol-gel method. This novel synthesis method has led to uniform distribution of the magnetostrictive and piezoelectric phases in the composite samples and improved magnetoelectric properties. Using autocombustion method CFO nanoparticles were synthesized and were added to the precursor gel of BCZT, further the composite powders were calcined at 800°C and sintered at 1300°C. Composite containing 50wt% CFO showed a maximum magnetostriction (λmax) of ~88ppm and strain sensitivity (dλ/dH) of ~41×10−9Oe−1. 40CFO-60BCZT composite showed a high piezoelectric voltage constant (g33) of 8×10−3Vm/N. All the composites showed magnetoelectric effect and the maximum magnetoelectric coupling coefficient (dE/dH=αME) was measured ~161mV/cm. Oe for 40CFO-60BCZT sample at its resonance frequency. The effect of microstructure on the magnetoelectric properties of [(x)CFO-(1-x)BCZT] composites has been studied and reported in this investigation as a function of its piezoelectric (BCZT)/ferrite (CoFe2O4) content.

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

ABSTRACTIn 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.

Enhanced electrical properties and observation of magnetoelectric effect in the BiFeO3–BaTiO3/CoFe2O4 laminate composites

This work investigates the electrical, magnetic and magnetoelectric response of the BiFeO3–BaTiO3/CoFe2O4 laminate composite which was prepared by the conventional solid-state sintering method. The results show that 0.6BiFeO3–0.4BaTiO3 phase and CoFe2O4 phase can coexist without any obvious chemical reaction in the composites under high sintering temperature. Compared with the magnetoelectric particulate composites, the laminate composites exhibit better electrical and magnetoelectric properties due to their higher resistivity and lower leakage current. The magnetoelectric behaviors were dependent on the relative mass ratio of the two phases, the frequency and the magnetic field. The largest magnetoelectric coefficient of the laminate composites reaches up to 26.2mV/cmOe at a bias magnetic field of 400Oe and a frequency of 5kHz, which is three times as large as that of the particulate composites (8.5mV/cmOe).

Magnetoelectric coupling in 0.5Pb(Ni1/3Nb2/3)O3–0.35PbTiO3–0.15PbZrO3 and CoFe2O4 based particulate composites

Particulate magnetoelectric composites of 1−x(0.5PNN–0.35PT–0.15PZ)+xCFO with x=0.1, 0.2, 0.3, and 0.4 were prepared by conventional solid state method. X-ray diffraction patterns confirmed the presence of the constituent phases present in composites. Backscattered SEM was used to identify different phases in the composites. Room temperature dielectric, ferroelectric, magnetic, magnetodielectric and magnetoelectric properties were studied for the prepared composites. A composite with x=0.3 has shown highest magnetoelectric voltage coefficient (αE) of 13.2mV/cm Oe. Due to the ability of responding to magnetic or electric field these materials are useful in practical applications like data storage and magnetic field sensors.

Electrical, magnetic and magnetoelectric properties of laminated 0.65BiFeO3-0.35BaTiO3/BiY2Fe5O12 composites

Magnetoelectric laminated composites of 0.65BiFeO3-0.35BaTiO3/BiY2Fe5O12 obtained by the conventional solid-state sintering method were investigated for their electrical, magnetic and magnetoelectric properties. The results show that 0.65BiFeO3-0.35BaTiO3 and BiY2Fe5O12 phases can coexist in the composites. Compared with the magnetoelectric particulate composites, the laminated composites have higher resistivity and lower leakage current. The magnetoelectric behaviors were strongly dependent on the relative mass ratio of the 0.65BiFeO3-0.35BaTiO3 and BiY2Fe5O12 phases. The largest magnetoelectric coefficient of the laminated composite reaches up to 7.25 mV cm−1 Oe at a bias magnetic field of 3000 Oe and a frequency of 70 kHz, which is twenty times as large as that of the particulate composite (0.36 mV cm−1 Oe).

Enhanced magnetoelectric properties of the laminated BaTiO3/CoFe2O4 composites

Magnetoelectric laminated composites of BaTiO3/CoFe2O4 were prepared by the conventional solid-state sintering method. The electrical, magnetic and magnetoelectric properties of the composites were investigated. The results show that BaTiO3 and CoFe2O4 phases can coexist in the composites. Compared with the magnetoelectric particulate composites, the magnetoelectric laminated composites have higher resistivities and lower leakage currents. The magnetoelectric behaviors are strongly dependent on the relative mass ratio of BaTiO3 and CoFe2O4. The largest magnetoelectric coefficient of the laminated composite reaches up to 135mV/cmOe at a bias magnetic field of 2600Oe and a frequency of 1kHz, which is four times as large as that of the particulate composite (35mV/cmOe).

Coordinate‐invariant phase field modeling of ferro‐electrics, part II: Application to composites and poly‐crystals

AbstractThis paper deals with the application of the model presented in the first part Schrade et al. [1] to ferroelectric composites filled with electrically conducting inclusions as well as to ferroelectric polycrystals. Composites are analyzed through the use of a computational homogenization framework for phase field methods proposed in Zäh &amp; Miehe [2]. This will give insights into the coupled phenomena taking place on the microscale and on their relation to the overall behavior. Both will be of special interest for the development of advanced composite materials with tailored properties like, for example, particulate magneto‐electric composites, which are composed of a ferroelectric matrix and magnetic rare‐earth elements or metals. Furthermore, we analyze the behavior of ferroelectric polycrystals with a focus on size effects. This will enable us to reveal preferred microstructure configurations depending on the system and grain size. In addition to that, it will serve as basis for the extraction of the directional properties of polycrystals with respect to their switching behavior in the different grains of the polycrystal. Associated simulations could then be used to supply coarser models with the needed directional informations. (© 2015 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Low temperature sintering and magnetoelectric properties of laminated BaTiO3/BiY2Fe5O12 composites

Magnetoelectric laminated composites of BaTiO3/BiY2Fe5O12 were prepared via the conventional solid-state sintering method, which were sintered at 1100°C. The electrical, magnetic properties and magnetoelectric effect of the composites were investigated. The results show that BaTiO3 and BiY2Fe5O12 phases can coexist in the composites. All the prepared composites exhibit excellent dielectric and ferroelectric properties. Compared with the magnetoelectric particulate composites, the laminated composites exhibit better electrical and magnetoelectric properties due to higher resistivity and lower leakage current. The magnetoelectric behaviors are strongly dependent on the relative mass ratio of BaTiO3 and BiY2Fe5O12, dc magnetic field, ac magnetic frequency, and the angle θ between the magnetic field and polarization direction. The largest magnetoelectric coefficient of the laminated composite reaches up to 14.36mV/cm Oe at a bias magnetic field of 600Oe and a frequency of 50kHz, which is sixty times as large as that of the particulate composite (0.24mV/cmOe).