Magnetoelectric Composite Ceramics Research Articles

Improvement of magnetoelectric coupling effect in Ba0.8Sr0.2TiO3-Co0.5Cu0.5Fe2O4 multiferroic fluids by tuning the composition

Ba0.8Sr0.2TiO3 (BST) and Cu0.5Co0.5Fe2O4 (CCFO) nanopowders were prepared by hydrothermal method and chemical coprecipitation, respectively. Barium strontium titanate nanopowder–nano mixed oxides containing copper, cobalt, and iron (BST-CCFO) multiferroic fluids with different mass ratios (mBST/mCCFO = 1:2, 1:1, and 2:1) were prepared by using dimethyl silicone oil and silane coupling agent. Effect of mass ratio on the magnetoelectric performance was comparatively investigated. X-ray diffraction (XRD) showed that the BST and CCFO powders had no secondary phases, which are tetragonal perovskite structure and cubic spinel structure, respectively. Scanning electron microscopy (SEM) showed that the average grain size of BST and CCFO was 26.34 nm and 26.82 nm, respectively. The agglomeration of BST nanopowder was serious. Under the external magnetic field, the BST-CCFO multiferroic fluid will form a chain structure due to the directional movement of magnetic particles, thus enhancing the dielectric properties and ferroelectric properties of multiferroic fluid. The chain structure under the action of magnetic field will change the motion of ferroelectric particles, so that the magnetoelectric coupling effect of multiferroic fluid is significantly enhanced, which is much higher than that of the same type of magnetoelectric composite ceramics. This study is expected to provide a new way to improve the magnetoelectric coupling effect of multiferroic materials.

Microstructure, Magnetodielectric, and Multiferroic Properties of xCo0.8Cu0.2Fe2O4−y(0.8BaTiO3–0.2BiAlO3) Composite Ceramics

Herein, xCo0.8Cu0.2Fe2O4−y (0.8BaTiO3–0.2BiAlO3) [xCCFO–y(BTO–BA)] (x = 0, y = 1; x = 1, y = 1; x = 1, y = 2; x = 1, y = 4; x = 1, y = 6) magnetoelectric composite ceramics are synthesized by solid‐state method. The effects of composition on the microstructure, dielectric, ferroelectric and magnetic properties are systematically investigated. Two‐phase structures were confirmed by X‐ray diffraction patterns, which correspond to (BTO–BA) and CCFO phases; a little impurity can be found, and this low‐concentration secondary phase is indexed as BaFe12O19. By scanning electron microscopy, it is found that all the samples show a uniform and relatively dense surface, while the grains show two different kinds of shapes and sizes, which are related with ferroelectric‐phase BTO–BA and magnetic‐phase CCFO. The average grain size of BTO–BA is ≈0.47 μm, and that of CCFO increases with increasing concentration of BTO–BA, and the size of BTO–BA is suppressed with the addition of CCFO. With decreasing the concentration of CCFO, the composites show more and more obvious magnetodielectric effect. The Curie temperature of BTO–BA ceramics is around 150 °C, but this value increases (higher than 150 °C) with the addition of CCFO, implying practical application in high‐temperature devices. The ferroelectric properties of composite ceramics can be optimized by adding BTO–BA.

The ac conductivity of magnetoelectric composite 0.85BiFeO3–0.15MgFe2O4

The features of the frequency dependence of conductivity and the current-voltage characteristics in magnetoelectric composite ceramics 0.85BiFeO3–0.15MgFe2O4 in the temperature range (300–500) K and frequencies (10–500) kHz are studied.

Structure, dielectric, piezoelectric, antiferroelectric and magnetic properties of CoFe2O4–PbZr0.52Ti0.48O3 composite ceramics

Magnetoelectric composite ceramics CoFe2O4–Pb(Zr0.52Ti0.48)O3(CFO-PZT) with different molar ratios (CFO/PZT = 1:4, 1:5, 1:6 and 1:7) were prepared by combining chemical coprecipitation and sol-gel method. The effects of molar ratio on the structure, dielectric and multiferroic properties were investigated. XRD results indicate that the composites show bi-phase structure, which can be indexed as CFO and PZT. SEM and EDS images present that the grain distribution is nonuniform, the average grain size of both CFO and PZT are near 1 μm, while they increase slightly with increasing the molar ratio. The dielectric constant is larger than 2000 in low frequency (<1 kHz) while it decreases to near 500 when the frequency is larger than 4 kHz. The dielectric loss of the sample (1:6) is the maximal, while the sample (1:5) shows the smallest one. The Curie temperature of PZT in the composites is is near 350 °C, which is larger than that of pure PZT sample (~330 °C), indicating the tuning effect of composition on the transition temperature. The samples present a very broad relaxation and higher disorder level, displaying dispersion behavior. The composites show antiferroelectric behavior in high frequency range while it can recover to normal ferroelectric property at low frequency. The antiferroelectric phenomenon gradually disappears after training effect. The composites with molar ratios of 1:4 and 1:6 exhibit better ferroelectricity and lower conductivity, the values of residual polarization (Pr) are 29.11 and 30.03 μC/cm2, respectively. The electrostrictive strain is 0.086% at 40 kV/cm when the molar ratio is 1:5, the sample (1:7) shows the smallest value (0.044%). All the samples show ferromagnetic properties, the magnetization decreases with increasing the PZT content. The saturation magnetization (Ms) and residual magnetization (Mr) of the samples decrease as the PZT content in the composite increases. Among them, the composite with the molar ratio of 1:4 shows better magnetic properties, the value of Mr and coercive field are respectively 1.67 emu/g and 404.26 Oe.

Effect of particle size on magnetodielectric and magnetoelectric coupling effect of CoFe2O4@BaTiO3 composite fluids

CoFe2O4 particles with two different sizes were prepared using hydrothermal method by controlling the technological parameters. On that basis, core–shell structure CoFe2O4@BaTiO3 (CFO@BTO) particles were prepared by sol–gel process. The surfactant treated composite particles were then distributed into a highly-insulating heptane to form CFO@BTO composite fluids. Influences of CFO particle size on the magnetodielectric and magnetoelectric coupling effect were comparatively investigated. XRD, TEM and SAED results indicate that the size of CFO particles are ~ 12 and ~ 18 nm, respectively, while the prepared CFO@BTO particles show bi-phase and core–shell composite structure, and the size of CFO@BTO particles are ~ 28 and ~ 35 nm, respectively. The composite fluids show quasi super paramagnetic behavior at room temperature due to the size effect and Brovnian motion. When the size of CFO is 18 nm, the CFO@BTO composite fluids shows larger remnant magnetization and coercive field. Strong dependence of dielectric properties on external magnetic field has been observed, of which the composite fluids show negative magnetodielectric effect, and the value of permittivity was decreased by 8% at 500 Oe. When size of CFO is 12 nm, the corresponding specimen with shows more obvious magnetic response, and it has larger remnant polarization. The values of both coercive electric field and remnant polarization of the two kinds of CFO@BTO composite fluids have been enhanced distinctly under the action of external magnetic field. When the particle size of CFO is smaller, the magnetolectric coupling coefficient αE of CFO@BTO composite fluid is larger, and this value decreases with increasing external magnetic field. When the particle sizes of CFO are 12 and 18 nm, the maximal values of αE are about 7 and 10 V/cm·Oe, respectively. These values are several orders of magnitude larger than that of CFO/BTO and other magnetoelectric composite ceramics. The strong coupling effect can be explained based on the formation, movement and variation of chain-like structure in the presence of external field. These results may supply useful information for enhancing coupling effect and might play important roles in practical applications in novel magnetoelectric devices.

Effects of molar ratio on dielectric, ferroelectric and magnetic properties of Ni0.5Zn0.5Fe2O4-BaTiO3 composite ceramics

Ni0.5Zn0.5Fe2O4-BaTiO3 (NZFO-BTO) magnetoelectric composite ceramics with different molar ratios (mNZFO:mBTO = 1:1.5, 1.5:1 and 2:1, defined as N1B1.5, N1.5B1 and N2B1, respectively) were prepared successfully by using a joint hydrothermal method and sol-gel technique and sintering at 1000 ?C. Meanwhile, the dielectric, ferroelectric and magnetic properties of the composites were investigated. The presence of bi-phase structure in the composites was verified with X-ray diffraction analyses. The scanning electron microscopy images and energy dispersion spectrum results confirmed that the bulk-like grains (2 to 5 ?m) and spherelike grains (_0.5 ?m) could be attributed to NZFO and BTO, respectively. The dielectric constant and loss increased with increasing NZFO/BTO molar ratio because the carrier concentration of NZFO is higher than that of BTO. Thus, the dielectric constant of the N2B1 ceramics is more than 7800 at low frequency of 100Hz and room temperature, while only less than 2000 for the N1B1.5 composite. Two peaks can be observed in the temperature dependence of the dielectric constant curves. One is near 120 ?C, which corresponds to the Curie temperature of BTO, while the other peak occurs at about 320 ?C, corresponding to the relaxation polarization. The remanent polarization increases with increasing the content of ferroelectric BTO. The maximum value at 1 kHz was observed for the N1B1.5 sample and it is larger than 4.5 ?C/cm2, while the minimal value was obtained for the N2B1 composite and is only 1.2 ?C/cm2. Magnetic properties were also measured and it was observed that magnetization increases with increasing the molar ratio. The largest saturation magnetization has the N2B1 composite (_51.74 emu/g) due to the larger concentration of NZFO phase. However, the sample N1B1.5 shows the largest coercive field due to the highest interface interaction. This study provides guidelines for the fabrication of NZFO-BTO magnetoelectric composite ceramics.

Microstructure, dielectric and enhanced multiferroic properties of Fe3O4/PbZr0.52Ti0.48O3 composite ceramics

Magnetoelectric composite ceramics Fe3O4/PbZr0.52Ti0.48O3 with different molar ratios (Fe3O4/PbZr0.52Ti0.48O3 = 1:1, 1:2 and 1:8) were prepared by combining hydrothermal method and sol–gel method, effects of molar ratio on the structure, dielectric and multiferroic properties were investigated. The results indicate that the synthesized composites show bi-phase structure, ruling out the presence of any obvious impurity phases. The grains can be divided into two types, the larger grain is attributed to PbZr0.52Ti0.48O3 while the smaller one can be considered to be Fe3O4. With the molar ratio increasing, the grain shape of PbZr0.52Ti0.48O3 changes from stripe to bulk-like while the shape and size of Fe3O4 is near the same. Both the dielectric constant and loss decrease with frequency, the specimen with the molar ratio of 1:8 shows the largest dielectric constant, while the sample has the lowest dielectric loss when the molar ratio is 1:2. With the increase of molar ratio, the height of the relaxation peak decreases and the peak position shifts to higher temperature. When the molar ratio is 1:8, the relaxation peak disappears due to less interface polarization. The remnant polarization increases with increasing the molar ratio, the maximum value is 1.12 μC/cm2, obtained at 1 kHz when the molar ratio is 1:8. Anomalous magnetic properties are observed, in which the magnetization increases first and then decreases with molar ratio, the largest saturation magnetization is ~ 30 emu/g when the ratio is 1:2 due to the strong interface interaction. The sample with the ratio of 1:1 shows the largest magnetic loss because of the highest content of magnetic phase. The magnetization shows a monotonic variation behavior with the molar ratio, indicating the strong interface interaction between the two phases. The maximal ME coupling coefficient is about 5.12 mV/(cm.Oe) for the sample 1:2 due to the stronger magnetic and ferroelectric properties.

Effect of Magnetic Phase on Structural and Multiferroic Properties of Ni1−xZnxFe2O4/BaTiO3 Composite Ceramics

Ni1−xZnxFe2O4/BaTiO3 (x = 0.3, 0.4, 0.5, 0.6, and 0.7) magnetoelectric composite ceramics have been prepared by combining the coprecipitation and sol–gel methods, and their structural and multiferroic properties studied and compared. The results indicate that the synthesized composites present biphase and composite structure, with no evident impurities observed. The lattice of the Ni1−xZnxFe2O4 crystal structure is distorted owing to the incorporation of Zn2+ ions. The samples present irregular microstructure and abnormal grain growth, which can be attributed to the heterogeneous distribution of the ferroelectric and magnetic phases during preparation. The chemical composition of the larger grains is Ni1−xZnxFe2O4, while that of the smaller grains is proven to be BaTiO3. The dielectric constant of the ceramics first increases then decreases as the Zn2+ ion content is increased, which is related to the irregular microstructure of the ceramics. Both the frequency dependence of the dielectric loss and the temperature dependence of the dielectric constant present two relaxation peaks for all samples. The dielectric loss peaks are attributed to the slow polarization process, such as turning-direction and space-charge polarization, while the dielectric constant peaks can be ascribed to the ferroelectric phase transition of BaTiO3 and relaxation polarization of the composites. The abnormal magnetization behaviors can be induced by the A–B superexchange interaction caused by the addition of nonmagnetic Zn2+ ions.

Magnetocapacitance and magnetoelectric coupling effect of Ni0.5Cu0.5Fe2O4/BaTiO3 mixed multiferroic fluids

Ni0.5Cu0.5Fe2O4/BaTiO3 (NCFO/BTO) mixed multiferroic fluids were prepared by distributing surfactant treated NCFO and BTO particles in to a highly-insulating base fluid, the magnetocapacitance and magnetoelectric coupling effect were investigated. The results indicate that the sample shows strong magnetoelectric coupling effect, in which both the coercive field Ec and remanent polarization Pr enhance obviously under the action of magnetic field, while the dielectric constant decreases with increasing the magnetic field, revealing negative magnetocapacitance phenomenon. Large direct magnetolectric coupling coefficient was estimated to be α ∼ 76 V/(cm−1.Oe), which is several orders of magnitude larger than that of conventional magnetoelectric composite ceramics. Further analysis indicates that the possibility of movement, aggregation and chain-like structure of the particles in the presence of external field is believed to be responsible for the observed negative magnetocapacitance and strong magnetoelectric coupling effect. The results show that the strong room temperature magnetoelectric effect of the mixed magnetoelectric fluids is the product of the deformation of the particle distribution and the utilization of clamping force under external field. This magnetoelectric coupling effect is different from that of conventional composite materials which is directly coupled via the interface interaction, which will be advantageous for practical applications.

In situ sol-gel co-synthesis at as low hydrolysis rate and microwave sintering of PZT/Fe2CoO4 magnetoelectric composite ceramics

Pb(Zr0.53Ti0.47)O3/Fe2CoO4 (PZT/Fe2CoO4) diphase particulate composites were prepared in an 80:20M ratio by the in situ sol-gel co-synthesis method. Controlling the hydrolysis rate of the metal-organic reagents used in the formation of the sol was essential to obtain a nanostructured system with a highly homogeneous and immiscible two-phase distribution. The compact diphase powders were densified throughout the microwave-assisted sintering methods for controlling grain growth, and to evaluate this new nanostructure and effect on the physical properties of this material. The characterizations revealed that the new in situ sol-gel co-synthesis method was successful in producing highly homogeneous nanopowders without secondary phases. The powders processed at low hydrolysis rates showed the formation of a core-shell particle architecture. After microwave-assisted sintering, the samples showed uniform distribution of the cobalt ferrite phase in the PZT phase, with an average nanograin size of about 300nm, while the same material sintered conventionally had an average cobalt ferrite grain size of about 6µm. Innovative PZT/Fe2CoO4 nanostructures were obtained with magnetoelectric response.

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).

In situ sol–gel co-synthesis under controlled pH and microwave sintering of PZT/CoFe2O4 magnetoelectric composite ceramics

This paper describes a novel sol–gel route for the in situ synthesis of heterostructure materials, and discusses the effects of two different pH levels on the characteristics of the raw powders and on the microstructure and electric properties of microwave-sintered PZT/CoFe2O4 (80/20) composites. The results indicate that the two pH levels evaluated here allowed for the successful production of biphasic nanocrystalline PZT/CoFe2O4 with two immiscible phases and without spurious phases. However, the synthesis performed in acid pH resulted in the formation of large self-assembled agglomerates without a well-defined structure, showing poor sinterability and inhomogeneous distribution of the two phases in the ceramic composite. In contrast, the powders synthesized in basic pH showed a more well-defined nanoparticle morphology with very small and uniform spherical particles. The microwave-sintered dense ceramic samples obtained in basic pH showed highly homogeneous distribution of the two constituent phases without percolation of the ferrite phase and, unlike the samples obtained by conventional sintering, they exhibited high electrical resistivity, confirming their greater phase integrity. This may be attributed to the adjustment of the synthesis parameters of nanocrystalline heterostructured materials prepared with PZT/CoFe2O4 raw powder, as well as the microwave sintering process, whose synergistic effect specifically improves the microstructure. The magnetoelectric response of these composites confirms their promising potential for application in multifunctional devices.

Reduced leakage current and improved ferroelectricity in magneto-electric composite ceramics prepared with microwave assisted radiant hybrid sintering

Structural, electrical and magnetic properties of magneto-electric composite ceramics viz., 0.9 BaTi0.95Sn0.05O3 (BTSO)- 0.1 Ni0.8Zn0.2Fe2O4 (NZFO) prepared with microwave assisted radiant hybrid sintering (MARH) are reported. Phase purity and isovalent substitution of Ti4+ by Sn4+ of the samples is confirmed from x-ray diffraction and 119Sn Mossbauer measurements respectively. Significant suppression of leakage current and improvement of ferroelectricity is observed for the composites prepared with MARH. The observed results are explained in terms of uniform dispersion of ferrite (NZFO) phase in the ferroelectric (BTSO) matrix as evidenced from back-scattered scanning electron micrographs.

LPF-doped core–shell structure based CFO/PLZT 0–3 magnetoelectric composite ceramics

Using LiF and PbF2 (mole ratio 1:1, LPF) as sintering additives, the xCoFe2O4/(1−x) Pb0.9025La0.065(Zr0.58Ti0.42)0.975Nb0.02O3 [x=0.1, 0.2, 0.3, and 0.4 in weight] (abbreviate as CFO/PLZT) 0–3 magnetoelectric (ME) composite ceramics were developed via a liquid phase sintering technique. A ZrO2 layer was coated on the CFO particles via a sol–gel method in order to inhibit the diffusion of Fe3+ and Co2+ ions from the ferrite CFO phase to the ferroelectric PLZT phase. With using 6wt% additives of LPF, dense composite ceramics can be obtained in a sintering temperature region of 1000–1150°C for 30min. Moreover, overall performance of the ceramics with relatively low CFO content (x=0.2) has been optimized. The effects of CFO content and sintering temperature on micromorphology, crystalline structure, piezoelectric, dielectric, and ME properties were investigated. It was found that the 0.2CFO/0.8PLZT composite ceramics exhibited a d33 of 80 pC/N and a ME coefficient of 102mV/Oecm at 215kHz.

Dielectric, magnetic and magnetoelectric properties of Ni0.5Zn0.5Fe2O4+Pb(Zr0.48Ti0.52)O3 composite ceramics

Magnetoelectric composite ceramics of spinel ferrite Ni0.5Zn0.5Fe2O4 (NZFO) with high magnetic permeability and tetragonal perovskite Pb(Zr0.48Ti0.52)O3 (PZT) with high piezoelectric constant were synthesized by common solid state reaction method. XRD and SEM showed that high dense composite ceramics without any foreign phases were obtained. The ceramics showed excellent dielectric and magnetic properties, which were stable in a large frequency range. The dielectric peak became wider with the ferrite content in the permittivity spectrum with temperature. With the increase in the ferrite content, the magnetic Curie temperature shifted to higher temperature and closed to that of the pure ferrite. In addition, the magnetoelectric coefficient enhanced as the increase in the ferrite content. The properties of the composite ceramics could be adjusted by the ferrite content. These research results provided a powerful experimental basis for the sensor and transducer in microelectronic and microwave devices.

Dielectric, ferromagnetic and maganetoelectric properties of BaTiO3–Ni0.7Zn0.3Fe2O4 composite ceramics

Lead-free magnetoelectric composite ceramics (1−x)BaTiO3–xNi0.7Zn0.3Fe2O4 (x=0.15, 0.3, 0.45) were successfully prepared by conventional oxide ceramic process. The tetragonal perovskite BaTiO3 and cubic spinel Ni0.7Zn0.3Fe2O4 were confirmed by X-ray diffraction. The dielectric behaviors of all composite samples show a normal response to the increasing measurement frequency and Ni0.7Zn0.3Fe2O4 ferrite content. Well defined ferromagnetic hysteresis loops and obvious magnetoelectric coupling effect are observed in the composite ceramics. The influence of applied dc bias magnetic field and Ni0.7Zn0.3Fe2O4 ferrite content on the magnetoelectric coupling responding voltage is investigated. The strongest peak magnetoelectric coupling voltage coefficient is 124μV/cmOe when x=0.3, which corresponds to the maximum magnetoelectric coupling responding voltage of 200μV.

Preparation and magnetoelectric characteristics of K0.5Na0.5NbO3-LiSbO3-BiFeO3/CuFe2O4 composite ceramics

The (1-x)(K0.5Na0.5NbO3-LiSbO3-BiFeO3)-xCuFe2O4 (x=0.1, 0.2, 0.3 and 0.4) magnetoelectric composite ceramics are prepared by the conventional solid-state reaction method. The microstructures and properties of the composite ceramics are characterized by X-ray diffractometer, scanning electron microscope and magnetoelectric coupling coefficient meter. The weak ionic interdiffusions between the phases K0.5Na0.5NbO3-LiSbO3-BiFeO3 and CuFe2O4 are observed and their particle sizes are well matched between each other. With the increase of CuFe2O4 content, the piezoelectric coefficient (d33) of the composite ceramics decreases from 130 pC/N to 30 pC/N and the magnetostriction coefficient (-λ) increases from 4.5×10-6 to 12.4×10-6. The magnetoelectric coupling coefficient (αE) of the composite ceramics first increases and then decreases with the CuFe2O4 content increasing. When the composition x=0.3, a maximum value of αE=9.4 mV·cm-1·Oe-1 is achieved.

Magnetoelectric composite ceramics of nickel ferrite and lead zirconate titanate via in situ processing

Magnetoelectric (ME) composite ceramics of NiFe2O4 (NFO) and lead zirconate titanate (PZT) were synthesized by a simple in situ processing based on a sol–gel method followed by a conventional sintering. X-ray diffraction patterns and scanning electron microscopy images revealed that this processing can produce two pure phases simultaneously. The in situ grown magnetic NiFe2O4 grains were well dispersed in the PZT matrix. The results demonstrated an attractive ME response of about 28.5 V cm−1 Oe−1 in the 0.35 NiFe2O4/0.65PZT at a resonance frequency of around 287 kHz.