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Magnetoelectric composite materials have attracted increasing attention because of their coupling between ferroelectricity and ferromagnetism. In this work, a new method has been used to prepare composite ceramics. Ferromagnetic phase Co(Fe1−xMnx)2O4 (x = 0.2, 0.4, 0.6, 0.8) with porous surfaces were prepared by annealing a metal organic framework (MOF) precursor (Fe1−xMnx)3[Co(CN)6]2·nH2O, and the ferroelectric phase BaTiO3 was grown in situ in the pores of Co(Fe1−xMnx)2O4 by a hydrothermal method. The structure, dielectric and ferroelectric properties of Co(Fe1−xMnx)2O4-BaTiO3 composite ceramics have been comparatively studied. XRD results indicate that with the increase of x, the crystalline structure of the ferromagnetic phase changes from CoFe2O4 (x = 0.2, 0.4) to CoMn2O4 (x = 0.6, 0.8) and SEM results show that the compactness of ceramics is better with increasing x. Because the conductivity of CoMn2O4 is far larger than that of CoFe2O4, the dielectric and ferroelectric properties of composite ceramics with x = 0.2 and 0.4 are better than that of x = 0.6 and 0.8. With the increase in the ratio of ferromagnetic and ferroelectric phases, the compactness of the ceramics was enhanced. Meanwhile, due to the higher conduction loss and leakage current of the ferromagnetic phase, the dielectric and ferroelectric properties of composite ceramics weaken with the increase of the ferromagnetic phase. [ABSTRACT FROM AUTHOR]

The effects of sintering temperature on the dielectric, ferroelectric, and magnetic performance of Co0.8Cu0.2Fe2O4@(Pb0.95La0.05)(Zr0.86Ti0.14)O3 (CCFO@PLZT) composite ceramics with core–shell structure were investigated. The X-ray diffraction results confirmed the bi-phase structure of the composites, with insufficient sintering temperature and inadequate reaction leading to the presence of Pb2O3 and ZrO2. Transmission electron microscope images showed that the core–shell structure was prepared, and the scanning electron microscope images showed that the average grain size of the ceramic samples increased with the increase of the sintering temperature. The dielectric constant does not change linearly as the sintering temperature rises, but tends to increase and then decrease, which could be owing to the fact the crystallinity of impurities increases, affecting their dielectric properties. The dispersion indices were 1.58, 1.64, 1.60, 1.61, and 1.70 with increasing temperature, indicating that the relaxation of CCFO@PLZT ceramics was enhanced. The residual polarization intensity (Pr) of CCFO@PLZT ceramics increased first and then decreased with increasing sintering temperature, reaching a maximum value of Pr ~ 1.849 μC/cm2 at 1050 °C, but this may be caused by the excessive leakage current. Grain growth, density reduction and partial reduction of Fe3+ ions to Fe2+ ions lead to a decrease in saturation magnetization intensity (Ms), residual magnetization intensity (Mr) and coercivity (Hc) with the increase of sintering temperature. [ABSTRACT FROM AUTHOR]

(K,Na)NbO3 − x at.% Tm2O3 (KNNTx) piezoelectric ceramics with submicron grain size were successfully prepared by solid-state method combined with microwave sintering. With the increase of content of Tm3+, KNNTx ceramics gradually transformed from orthorhombic (O) phase to the coexistence of O and tetragonal (T) phase at room temperature, and the phase transition temperature of O–T phase shifted to low temperature region. The leakage behaviors, dielectric, ferroelectric, and piezoelectric properties of KNNTx ceramics depend on the structure evolution, cationic vacancy and grain refinement caused by Tm3+ doping, and the relevant mechanisms have been illustrated. The substitution of Tm3+ at A sites increases the critical driving force for the rapid growth of grains and obviously refine the grain of KNNTx ceramics, resulting in its deteriorated ferroelectricity and enhanced piezoelectricity. Especially the piezoelectric constant of KNNTx ceramics increased from 109.8 to 163.6 pC/N. These findings are of great significance for developing excellent lead-free piezoelectric materials. [ABSTRACT FROM AUTHOR]

Purpose: To explore the improvement of its low temperature aging resistance by co-doping oral 3Y-TZP with TiO2 and GeO2. Methods: After the samples of 3Y-TZP co-doped with GeO2 and TiO2 were prepared by mechanical ball milling, drying, and pressureless sintering, the microstructure was studied by scanning transmission electron microscope, energy spectrometer, and high angle annular dark field detector. After treatment in the autoclave, the conversion of all samples was measured by XRD. Results: After mechanical ball milling for 24 hours, the particle size of the composite powder of 3Y-TZP co-doped with GeO2 and TiO2 is uniform, distributed at about 50 nm, the particle shape is basically spherical, the dispersion is good, but there is a small amount of agglomeration; Tetravalent stabilizers (Ge 4 + , Ti 4 + ) can inhibit the low-temperature aging effect of zirconia materials. With the increase of germanium oxide doping, the hydrothermal degradation resistance of zirconia can be improved. GeO2 doped 3Y-TZP has better low temperature aging resistance than TiO2 doped 3Y-TZP. With the increase of dopant content, the degree of grain boundary segregation increases, but even if the doping amount of Ge 4 + is small, the degree of grain boundary segregation can be comparable to that of Ti 4 + with a large doping amount. Conclusion: In this paper, the composite powder of 3Y-TZP co-doped with GeO2 and TiO2 with uniform particle size and good dispersion was prepared by mechanical ball milling. The preparation process is simple, the energy consumption is low, and the cumbersome processes of the co-precipitation method and liquid-phase method are avoided. On the other hand, adding GeO2 and TiO2 can enhance the low-temperature aging resistance of 3Y-TZP ceramics. GeO2 is superior to TiO2 in low-temperature degradation resistance, which can be used as the first choice. This study contributes to the research on doping cations of dental zirconia and provides a reference for dentists to choose a reasonable zirconia material. [ABSTRACT FROM AUTHOR]

Purpose: To explore the improvement of its low temperature aging resistance by co-doping oral 3Y-TZP with TiO2 and GeO2. Methods: After the samples of 3Y-TZP co-doped with GeO2 and TiO2 were prepared by mechanical ball milling, drying, and pressureless sintering, the microstructure was studied by scanning transmission electron microscope, energy spectrometer, and high angle annular dark field detector. After treatment in the autoclave, the conversion of all samples was measured by XRD. Results: After mechanical ball milling for 24 hours, the particle size of the composite powder of 3Y-TZP co-doped with GeO2 and TiO2 is uniform, distributed at about 50 nm, the particle shape is basically spherical, the dispersion is good, but there is a small amount of agglomeration; Tetravalent stabilizers (Ge 4 + , Ti 4 + ) can inhibit the low-temperature aging effect of zirconia materials. With the increase of germanium oxide doping, the hydrothermal degradation resistance of zirconia can be improved. GeO2 doped 3Y-TZP has better low temperature aging resistance than TiO2 doped 3Y-TZP. With the increase of dopant content, the degree of grain boundary segregation increases, but even if the doping amount of Ge 4 + is small, the degree of grain boundary segregation can be comparable to that of Ti 4 + with a large doping amount. Conclusion: In this paper, the composite powder of 3Y-TZP co-doped with GeO2 and TiO2 with uniform particle size and good dispersion was prepared by mechanical ball milling. The preparation process is simple, the energy consumption is low, and the cumbersome processes of the co-precipitation method and liquid-phase method are avoided. On the other hand, adding GeO2 and TiO2 can enhance the low-temperature aging resistance of 3Y-TZP ceramics. GeO2 is superior to TiO2 in low-temperature degradation resistance, which can be used as the first choice. This study contributes to the research on doping cations of dental zirconia and provides a reference for dentists to choose a reasonable zirconia material. [ABSTRACT FROM AUTHOR]

BaFe12O19 (BaM) powders and their corresponding ceramics were prepared by the sol–gel method at different solution concentrations (0.195–0.325 mol/L). The effects of solution concentration on microstructure, surface morphology, electrical properties, and magnetic properties of BaM powder BaM ceramics were systematically studied. XRD results show that the powders are pure BaM phase. SEM results show that with the increase in solution concentration, the grain size of ceramic increases, and the grain size of hexagonal sheet structure decreases gradually. At room temperature, when the solution concentration is 0.195 mol/L, ceramics' saturation polarization intensity and residual polarization intensity reach the maximum, which are 0.528 μC/cm2 and 0.297 μC/cm2, respectively. When the solution concentration is 0.325 mol/L, the ferroelectric properties of ceramic deteriorate due to the influence of leakage current. The ferroelectric hysteresis loop and magnetic hysteresis loop of ceramics show the multiferroic properties of ceramics at room temperature, which provides a new choice for single-phase multiferroic materials and lays a foundation for the multi-functionalization of BaM devices. [ABSTRACT FROM AUTHOR]

Multiferroic composite ceramics xNi0.15Cu0.25Zn0.6Fe2O4-(1-x) Ba0.85Ca0.15Zr0.1Ti0.9O3 (x = 0, 0.2, 0.3, 0.4, 0.5, 0.6, 0.9 and 1) were prepared by combining chemical co-precipitation method with sol–gel method; the microstructure, dielectric, ferroelectric, magnetic and multiferroic properties were comparatively investigated. XRD results show that all the specimens have obvious bi-phases structure. The grains with larger size are magnetic phase Ni0.15Cu0.25Zn0.6Fe2O4(NCZF), while that of smaller size can be attributed to ferroelectric phase Ba0.85Ca0.15Zr0.1Ti0.9O3(BCZT). The dielectric constant of the sample with x = 0.6 is the largest at low frequency but the specimen x = 0.2 has the highest value of dielectric constant in high-frequency region. When x = 0.9, the ceramic has the largest loss, while it presents the lowest loss value when x = 0.3. The height of the peak decreases with increase in the frequency, and the position of the peak moves to higher temperature range with the decrease in x. The dielectric loss increases sharply with temperature, especially when x = 0.9, when the temperature is higher than 300 °C, the dielectric loss reaches hundreds of times under low frequency. Al samples present apparent ferroelectric hysteresis loops, but further characterization shows that the hysteresis may be attributed to leakage current. The remnant polarization(Pr) and coercive field(Ec) do not monotonically change with x, Pr is 0.1576 μC/cm2 at 2 kHz when x = 0.6. The magnetization monotonically changes with the x, indicating that there is a strong interfacial interaction between the two phases. Under the action of an external magnetic field of 1 mT, the magnetoelectric (ME) coupling is the strongest (relative polarization change 37%) when x = 0.2. [ABSTRACT FROM AUTHOR]

The Ca3Ti2O7 materials exhibit hybrid improper ferroelectricity due to the rotation and tilt coupling of TiO6 octahedron. However, the lower remnant polarization of Ca3Ti2O7 ceramics obtained by conventional solid-state method limits its practical application. Herein, the single-phase Ca3Ti2O7 ceramics with enhanced ferroelectricity were synthesized using an acetic acid sol–gel method and two-stage sintering. The sintering process does not significantly change the distortion amplitude of TiO6 octahedron in Ca3Ti2O7 ceramics but has a greater impact on the grain size and the concentration of oxygen vacancy. The synergistic effects of grain size and oxygen vacancy have been achieved in the Ca3Ti2O7 ceramics prepared by the optimal sintering process (1400 °C/12 h − 1550 °C/18 h), which leads to its enhanced hybrid ferroelectricity (Pr = 1.34 μC/cm2 and EC = 120 kV/cm). These findings demonstrate that the sol–gel method is an effective approach to obtain the Ca3Ti2O7 materials with enhanced hybrid improper ferroelectricity. [ABSTRACT FROM AUTHOR]

Magnetoelectric composites have attracted much attention due to their strong magnetoelectric coupling effect. In this paper, PbTiO3-NiFe2O4 (PTO/NFO) composite ceramics were prepared by sol-gel method. Effect of sintering temperatures on the structure, dielectric properties and multiferroic properties were studied. XRD results show that PTO/NFO ceramics have been successfully prepared. When the sintering temperature is 1050 °C, the secondary phase PbO2 exists in the ceramics. SEM results show that there were two kinds of grains with different sizes. EDS analysis suggested that the large particles are NFO and the small particles are PTO. The sintering temperature has a great influence on the dielectric and ferroelectric properties of the prepared ceramics. When the sintering temperature is 950 °C, the ceramics show the maximum dielectric constant at low frequency. When the sintering temperature is 1150 °C, the maximum residual polarization is 1.236 μC/cm2. The conductive mechanism of ceramics is dominated by Space Charge – Limited Conduction. The remanent magnetization and coercive field decrease with increasing the sintering temperature. The magnetoelectric coupling coefficient shows that ceramics have strong magnetoelectric coupling performance (5.7 V/cm·Oe). [ABSTRACT FROM AUTHOR]

To enhance the piezoelectric responses, Ba0.85Ca0.15Zr0.1Ti0.9O3 (BCZT) ceramics were fabricated by a sol–gel method in various sintering atmospheres. The effects of oxygen partial pressure on the microstructure and electrical properties of BCZT ceramics were systematically investigated. The samples sintered in air, O2 and N2 are the coexistence of the orthorhombic (O)-tetragonal (T) phase at room temperature. The phase transition temperature of the O–T phase of BCZT samples sintered in air, O2 and N2 is gradually closer to room temperature. The results of EDS, XPS and the activation energy confirm the significant effect of oxygen sintering atmosphere. BCZT samples sintered in oxygen atmosphere show excellent ferroelectricity (2Pr = 31.62 μC/cm2, 2EC = 3.46 kV/cm) and significantly enhanced piezoelectricity (d33 = 604.3 pC/N, d33* = 647.5 pm/V and kp = 58%), resulting from the minimum oxygen vacancy, the phase transition temperature of O–T closer to room temperature and dense microstructure. These results demonstrate that adjusting oxygen partial pressure in sintering is an effective way to enhance the piezoelectric responses of BCZT ceramics. [ABSTRACT FROM AUTHOR]

Magnetoelectric composite materials have attracted more and more attention because of their coupling of ferroelectricity and ferromagnetism. It is a hotspot to realize the combination of ferromagnetic phase and ferroelectric phase. In this work, we used a new strategy to prepare CoFe 2 O 4 /BaTiO 3 composite ceramics: firstly, porous ferromagnetic CoFe 2 O 4 phase was prepared by annealing of MOFs (metal organic frameworks) precursor Fe 3 [Co(CN) 6 ] 2. And then, the ferroelectric BaTiO 3 phase in-situ grew in the pores of CoFe 2 O 4 by a hydrothermal method. In the end, the CoFe 2 O 4 /BaTiO 3 composite ceramics sintered at different temperatures have been synthesized. The effects of sintering temperature on the structure, dielectric and ferroelectric properties have also been studied. Because the crystallinity and density increase with the increase of sintering temperature, the composite ceramic sintered at 1200 °C shows the best dielectric properties. It is found that sintering temperature has little effect on the ferroelectric and magnetic properties of ceramics. Taking the CoFe 2 O 4 /BaTiO 3 composite ceramic sintered at 1200 °C as an example, derived from the interaction between the ferromagnetic CoFe 2 O 4 phase and ferroelectric BaTiO 3 phase, the applied magnetic field lead to the reduction of P r and E c. [ABSTRACT FROM AUTHOR]

Cutting performance and wear mechanism of spark plasma-sintered Si3N4 (SN91) and Si3N4/WC (SW10) ceramic tools in the dry turning of 41Cr4 hardened steel are studied. SN91 tool shows better wear resistance than SW10 tool and commercial ceramic tool SW500 and cemented carbide tool YG8 under the same cutting conditions. The better cutting performance of SN91 can be attributed to its excellent high-temperature flexural strength. The most significant factor affecting the tool life of SN91 is the cutting speed. A higher material removal volume can be achieved at a low cutting speed, large depth of cut, and large feed rate. A long cutting distance/time can be achieved at a low cutting speed, small depth of cut, and feed rate. At a cutting speed of 103.62 m/min (ap = 0.1 mm, and f = 0.05 mm/rev), the wear mechanisms of SN91 are adhesion, oxidation, and diffusion, and no crater wear is observed on the rake face. At a cutting speed of 214.31 (ap = 0.3 mm and f = 0.05 mm/rev) and 314 m/min (ap = 0.2 mm and f = 0.05 mm/rev), the failure forms of SN91 tool are mainly rake face crater wear and flank wear; the wear mechanisms of rake face are diffusion, abrasion, and oxidation; and the wear mechanisms of flank face are abrasion, adhesion, and oxidation. The failure forms of SW10 tool are mainly rake face crater wear and flank wear, and the wear mechanisms are diffusion, abrasion, adhesion, and oxidation. [ABSTRACT FROM AUTHOR]

Ni0.5Zn0.5Fe2O4/Ba0.8Sr0.2TiO3 (NZFO/BST) composite ceramics with different additions of Bi2O3 (0%, 1%, 3%, and 5% wt) were synthesized via the solid-phase sintering method. XRD analysis indicates that the composite ceramics show bi-phase structure, without apparent secondly phases can be observed. SEM images show that all the specimens have relative dense structure, the grain size is in the range 1–2 μm. A certain amount of Bi2O3 is beneficial to grain growth, the average grain size of NZFO/BST ceramics increases from 179 to 297 nm when the concentration of Bi2O3 is 0 and 3%, respectively. EDS results indicate that the distribution of NZFO phase and BST phase is not uniform. The sample NZFO/BST-3%Bi2O3 not only has the largest dielectric constant (εr) in the whole temperature range (25–500 °C), but also presents the smallest dielectric loss (tanδ) at high temperature region (> 400 °C), and the maximum tanδ value is less than 0.4 for all the samples, indicating excellent dielectric performance. Compared with other samples, the specimen NZFO/BST-3%Bi2O3 has the largest remnant polarization (~ 1.14 μC/cm2). The sample NZFO/BST-3%Bi2O3 has the largest leakage current density, while the ceramic NZFO/BST-5%Bi2O3 presents the opposite behavior, the value of leakage current of the sample NZFO/BST-3%Bi2O3 is about 7 times larger than that of the specimen NZFO/BST-5%Bi2O. All the composite ceramics show soft magnetic behavior, since Bi2O3 is a non-magnetic phase, addition of Bi2O3 will dilute the magnetic moment per unit volume so as to decrease the magnetic properties of the ceramics. The sample NZFO/BST-3%Bi2O3 has the second largest saturation magnetization (Mr) of 11.27 emu/g and the smallest coercive field (HC) ~ 3.54 Oe. All the samples show strong magnetoelectric coupling effect, the highest magnetoelectric coupling coefficient is ~ 47 Vcm−1Oe−1, which was obtained in the sample without addition of Bi2O3. In short, the addition of Bi2O3 not only affects the structure of composite ceramics, but also plays an important role in affecting the magnetoelectric performance. [ABSTRACT FROM AUTHOR]

Ni0.5Zn0.5Fe2O4/Ba0.8Sr0.2TiO3 (NZFO/BST) magnetoelectric composites were synthesized through traditional solid-phase method, and effects of IrO2 addition on the microstructure, surface appearance and magnetoelectric properties were comparatively investigated. XRD patterns demonstrate a spinel structure of NZFO and tetragonal perovskite structure of BST, and the addition of IrO2 is conducive to improving the crystallinity of materials. SEM presents that a certain amount of IrO2 is beneficial to the growth of ceramic grains and the densification of ceramics. Through SEM and EDS analysis, it is found that the smaller grain size is BST, and its size is about 100 nm. Sample NZFO/BST-5% has the largest average grain size (~ 277.51), while sample NZFO/BST-1% has a relative density of 91.23%. The relaxation behavior is more obvious with the addition of a certain content of IrO2, which leads to the increase of dielectric constants. In the high temperature region (> 200 ℃), the sample exhibits a large dielectric loss, particularly, the more the content of IrO2, the more obvious this phenomenon is. The addition of IrO2 causes the larger leakage current of NZFO/BST composites so that samples NZFO/BST-3% and NZFO/BST-5% exhibit poor ferroelectricity, in addition, the magnetic properties of the sample are also weakened, and the NZFO/BST composites exhibited a soft ferromagnetic behavior. [ABSTRACT FROM AUTHOR]

Ba0.7Sr0.3TiO3 ceramics has been synthesized by solid state reaction method. The effects of sintering time on microstructure and electric properties of Ba0.7Sr0.3TiO3 ceramics have been investigated. XRD patterns show that all ceramic samples are single tetragonal phase. The grain size increases with sintering time. Ba0.7Sr0.3TiO3 ceramics show obvious relaxor behavior because of its broadening dielectric peaks and frequency dispersion phenomenon. As sintering time increases, the Curie temperature does not change significantly and the diffuseness of the phase transition of Ba0.7Sr0.3TiO3 ceramics slightly enhances. Moreover, the remnant polarization and coercive field have no obvious changes with the increasing of sintering time. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

(Ca1−xSrx)3(Ti1−yMny)2O7 (CSTMO) ceramics with hybrid improper ferroelectricity were prepared by conventional solid-state reaction method. Effect of Sr2+ and Mn4+ contents on microstructure, dielectric and ferroelectric properties have been systematically investigated. The XRD results show that CSTMO ceramics is single phase with orthorhombic structure. The lattice constants and average grain size increase with the increasing of Sr2+ content and decrease with the increasing of Mn4+ content. The introduction of Mn4+ deteriorates the densification of CSTMO ceramics to some extent, and the substitution of Sr2+ with higher content can improve the densification by promoting a rapid interdiffusion movement via grain-boundary. (Ca0.8Sr0.2)3(Ti0.9Mn0.1)2O7 ceramics present the highest dielectric constant and dielectric loss, while the dielectric loss of (Ca0.8Sr0.2)3(Ti0.95Mn0.05)2O7 ceramics has a significant reduction. The leakage current of CSTMO ceramics decreases with the increasing of Sr2+ and Mn4+ content. The leakage behavior suggests that the Ohmic conduction and Schottky emission dominate the leakage current of CSTMO ceramics. Moreover, the remnant polarization decreases with the increasing of Sr2+ because of its suppression for the rotating and tilting angle (a−a−c+) of oxygen octahedron. And the electrical polarization decreases with the increasing of Mn4+ content due to the instability of MnO6 rotation. [ABSTRACT FROM AUTHOR]

Flash sintering is novel, innovative, and promising technique for achieving highly dense ceramic materials at low furnace temperature and short sintering time. Herein, flash sintering process was studied by reducing furnace temperature while the electric field applied to samples was kept constant. Further, 8 mol% yttria-stabilized zirconia (8YSZ) samples were sintered by current-limiting flash sintering mode during the occurrence of this flash sintering process. Results showed that the lower the furnace temperature, the longer the time for the onset of flash sintering. However, temperature threshold was observed under certain electric field. Resulting flash sintered 8YSZ samples were characterized by scanning electron microscopy (SEM) and electrochemical impedance spectroscopy (EIS). SEM images exhibited well-dense microstructures with small grain size. EIS results indicated that the values of conductivity of all 8YSZ samples flash sintered at different furnace temperatures were almost similar, and the conductivity of 8YSZ flash sintered at 565 °C reached 0.056 S cm −1 at 850 °C under the electric field of 300 V cm −1 , which is adequate for solid oxide fuel cells application. [ABSTRACT FROM AUTHOR]

(0.9 – x)BaTiO3–0.1BiYbO3–xBiAlO3 (x = 0, 0.02, 0.04, and 0.08) lead‐free ferroelectric ceramics are synthesized using conventional sintering (CS) and microwave sintering (MWS) methods. The microstructure, dielectric and ferroelectric properties, relaxation behavior, and energy storage properties are investigated systematically. X‐ray diffraction (XRD) patterns show a single perovskite phase for all samples. Scanning electron microscope (SEM) images indicate that MWS method can impede the grain growth, whereas the introduction of BiAlO3 can lead to the increase in the grain size. Dielectric measurements reveal that an obvious dielectric relaxation behavior can be strengthened by MWS, and the improvement of the dielectric constant (εr) of ceramics is realized by MWS. Incorporated with BiAlO3 contributes to enhancement of the frequency and temperature stabilities of the dielectric constant for BaTiO3–BiYbO3 ceramics. The slim hysteresis loops are observed, and the maximum polarization of the sample sintered by MWS is higher than that sintered by CS. The MWS samples possess a higher energy density which is about 2 times larger than that of CS samples, and the largest energy storage density ≈0.86 J cm−3 and energy storage efficiency ≈97.44% are, respectively, obtained at x = 0 and 0.04 for MWS ceramics. [ABSTRACT FROM AUTHOR]

The n-SiC (nanometer SiC) is added to be the additive in order to improve the mechanical performance of Si3N4 ceramics. A microwave sintered the ceramics at different temperature and holding times. The results shows that the Si3N4/n-SiC ceramics (85 wt% Si3N4 + 5 wt% n-SiC + 5 wt% Al2O3 + 5 wt% Y2O3) have the best mechanical properties at 1600 °C, which is beneficial to the densification and β-Si3N4 phase formation for 10 min: the density, hardness, and fracture toughness were 97.1%, 14.44 GPa, and 7.77 MPa·m1/2, which increased by 2.8%, 7.0%, and 13.1%, respectively, when compared with the ceramics (90 wt% Si3N4 + 5 wt% Al2O3 + 5 wt% Y2O3). [ABSTRACT FROM AUTHOR]

Low remnant polarization and high coercive field are the main factors limiting the practical application of Ca 3 Ti 2 O 7 -based hybrid improper ferroelectric ceramics. Based on sol-gel method and soft doping effect, (Ca 1- x Nd x) 3 Ti 2 O 7 (x= 0.003) ceramics with higher remnant polarization of ∼3.53 μC/cm2 and lower coercive field of ∼91 kV/cm were obtained. More interestingly, thanks to the large distortion amplitude of TiO 6 octahedron and effective suppression of defects such as oxygen vacancies caused by Nd3+ as a donor dopant, the remnant polarization of (Ca 1- x Nd x) 3 Ti 2 O 7 (x = 0.003 and 0.006) ceramics measured at 10 Hz using the DHM mode were as high as 7.33 μC/cm2 and 5.85 μC/cm2. These findings prove that the soft doping at A sites of Ca 3 Ti 2 O 7 material is a simple and effective strategy to enhance its hybrid improper ferroelectricity. [ABSTRACT FROM AUTHOR]

(1 − x)BaTiO3–xBiAlO3 relaxor ferroelectric ceramics were prepared by the conventional sintering (CS) and the microwave sintering (MWS) methods, respectively. The microstructure, the dielectric properties, the relaxation characteristic, the ferroelectric and the energy storage properties were investigated in detail. The results show that a single perovskite phase exists in ceramic samples sintered by CS and MWS. The addition of BiAlO3 into BaTiO3 and the MWS method result in the reduction of the grain size and the porosity of BaTiO3 ceramic. This leads to the enhanced diffuse transition and frequency dispersion. The dielectric constant and loss decrease with increasing the BiAlO3 content, and the temperature and the frequency stabilities are enhanced by introducing BiAlO3 into BaTiO3. The remnant polarization (Pr) increases initially and then decreases with the increase of BiAlO3 content, the maximum values of Pr (9.5 μC/cm2 for CS and 7.27 μC/cm2 for MWS) are obtained at x = 0.02. The addition of BiAlO3 can elevate the variation of polarization ΔP (Pmax − Pr), its maximum values (12.56 μC/cm2 for CS ceramic and 12.2 μC/cm2 for MWS ceramic) are acquired at x = 0.04, 0.08, respectively. The energy storage properties indicate that the energy storage density (Wrec) increases, while the energy storage efficiency (η) firstly decreases and then increases with the increase of x. [ABSTRACT FROM AUTHOR]

As an important renewable energy, hydrogen energy becomes an important part of the future energy system. Proton ceramic electrolysis cell (PCEC) enables the efficient, clean, large-scale preparation of hydrogen, which is a new type of energy conversion device, attracting the attention of many researchers. Sr 2 Fe 1.4 Zn 0.1 Mo 0.5 O 6-δ (SFZM) anode materials were developed to investigate the effect of B-site doping of Zn on the electrochemical properties of the Sr 2 Fe 1.5 Mo 0.5 O 6-δ (SFM) materials. The results reveal that the doping of Zn increases the concentration of oxygen vacancies and improves the electrocatalytic activity, which in turn improves the performance of the material. A current density of 408 mA cm−2 has been achieved at 1.3 V when the SFZM-based single cell was operated in an electrolysis mode (50% H 2 O in air) at 600 °C, higher than SFM-based single cells (286 mA cm−2 at 1.3 V). In addition, the SFZM-based single cell exhibited good durability in a stability test at an electrolysis current density of 408 mA cm−2. This work confirms that SFZM is a promising material for proton ceramic electrolysis cell anode. [ABSTRACT FROM AUTHOR]

Ca 3 (Ti 1- x Co x) 2 O 7 ceramics were prepared by a tartaric acid sol-gel method and sintered in an oxygen atmosphere. The introduction of Co2+/Co3+ as acceptor dopants leads to the formation of more oxygen vacancies and defect dipoles in Ca 3 (Ti 1- x Co x) 2 O 7 ceramics. Oxygen vacancy and defect dipoles lead to the transition of dielectric, leakage, and ferroelectric behaviors of Ca 3 (Ti 1- x Co x) 2 O 7 ceramics. The coexistence of hybrid improper ferroelectricity and ferromagnetism at room temperature in Ca 3 (Ti 1- x Co x) 2 O 7 ceramics has been successfully realized through the superexchange interaction of Co–O–Co. Ca 3 (Ti 1- x Co x) 2 O 7 ceramics exhibit superior ferroelectricity (the remnant polarization is 3.29 μC/cm2) and enhanced ferromagnetism (the remnant magnetization reaches 6.4×10−3 emu/g). This strategy based on the introduction of transition metal ions with unfilled 3d shells at B sites is an important approach to realize novel room-temperature single-phase multiferroic materials for Ca 3 Ti 2 O 7 -based materials. [ABSTRACT FROM AUTHOR]

One kind of Al 2 O 3 /Ti(C,N) micro-nano-composite ceramic tool material with acceptable properties was prepared by microwave sintering. Effects of sintering temperature and holding time on densification, mechanical properties and microstructure were studied. The optimal relative density, fracture toughness and Vickers hardness were 98.4±0.30, 6.72±0.28 MPa m 1/2 and 18.42±0.59 GPa, respectively, which were obtained at 1550 °C for 10 min. Compared to the conventional sintering, the sintering temperature and holding time of microwave sintering were reduced by 14% and 89%, respectively. The microwave sintering made the sizes of some particles keep in nano-scale, which leaded to the formation of intragranular structures. The residual stress in the intragranular structures increased the ratio of grain boundary toughness to grain toughness of matrix ( K cb / K cg ), and thus the micro-Al 2 O 3 grains were more inclined to transgranular fracture. [ABSTRACT FROM AUTHOR]

Ba 0.85 Ca 0.15 Zr 0.1 Ti 0.9 O 3 (BCZT) ceramics with super large grain size (>50 μm) have been successfully fabricated by sol-gel method. The effects of pH value of precursor solution on microstructure, electric properties and fatigue behavior were systematically studied. BCZT ceramics with super large grain size (35–55 μm) were prepared by BCZT powders with large particle size (136–221 nm) by controlling the pH value. The grain size and densification of BCZT ceramics decrease with the increase of pH value of precursor solution. XRD results indicate that there is the coexistence of rhombohedral and tetragonal phase in BCZT ceramics synthesized by precursor solution with a pH of 3 and are the coexistence of orthorhombic and tetragonal phase in BCZT ceramics synthesized by precursor solution with a pH of 5 and 7. BCZT ceramics shows obvious diffuse ferroelectric-paraelectric phase transition characteristic and the diffuseness behavior enhances as the pH value increases. The remnant polarization and coercive electric field of BCZT ceramics reduce with the decreased grain size caused by the increase of pH value. The excellent piezoelectric properties (d 33 = 585.6 pC/N and d 33 ∗ = 898 pm/V) of BCZT ceramics have been obtained by super large grain size and the construction of phase boundary of tetragonal phase and orthorhombic phase. Furthermore, BCZT ceramics with large grain size still has high fatigue resistance to bipolar electric cycling. • BCZT ceramics with super large grain size (>50 μm) are obtained. • Enhanced piezoelectric properties (d 33 = 585.6 pC/N and d 33 ∗ = 898 pm/V) are obtained. • High piezoelectric response results from super large grain size and phase boundary. [ABSTRACT FROM AUTHOR]

Mn 0.5 Mg 0.5 Fe 2 O 4 /Ba 0.8 Sr 0.2 Ti 0.9 Zr 0.1 O 3 composite ceramics were prepared by sol-gel method and the effects of molar ratio (3:1, 2:1, 1:1, 1:2, 1:3) between the magnetic and ferroelectric phases on the microstructure, dielectric, ferroelectric and magnetic properties have been comparatively investigated. The results indicate that the obtained composite ceramics show bi-phase structure, without other apparent impurities. The surface is relatively uniform except for some pores, and the grain size of all the samples is near 1 μm. The dielectric constant shows decreasing trend with the molar ratio while the loss presents the opposite behavior. Only one relaxation peak can be observed when the molar ratio is less than 1:1, but two peaks are found when the molar ratio exceeds 1:1. The height of the peak decreases with the frequency and molar ratio while the position shifts to higher temperature range with the molar ratio. The dielectric loss increases sharply with the temperature and it is amounts to several thousand when the temperature is lager than 300 °C in the lower molar ratios. Both the resident polarization and coercive electric field increase with the measured voltage while they decrease with the frequency. The leakage current decreases with the molar ratio due to the lower conductivity of Mn 0.5 Mg 0.5 Fe 2 O 4. 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 800 mV/(cm.Oe) for the sample 3:1 due to the stronger magnetic properties. • Mn 0.5 Mg 0.5 Fe 2 O 4 /Ba 0.8 Sr 0.2 Ti 0.9 Zr 0.1 O 3 composites were prepared by sol-gel method. • The obtained composite ceramics show bi-phase structure, with the grain size of all the samples is near 1 mm. • Relaxation peaks can be observed in the temperature dependence of dielectric constant. • The magnetization shows abnormal behavior due to the strong interface interaction between the two phases. [ABSTRACT FROM AUTHOR]

Abstract High performance multiferroic composites have attracted great attentions because they are more beneficial to increasing magnetoelectric coupling effect. We report the effects of molar ratio (4:1, 2:1, 1:1, 1:2 and 1:4) on the structural, dielectric and multiferroic properties of Co 0.6 Cu 0.3 Zn 0.1 Fe 2 O 4 /Ba 0.9 Sr 0.1 Zr 0.1 Ti 0.9 O 3 (CCZFO/BSZTO) composite ceramics prepared by sol-gel method. The XRD results confirm successful formation of the CCZFO/BSZTO composites without presence of any impurity phase. The mean grain size is about 1.5 mm and it shows double dispersing behavior, the larger grains belong to CCZFO while the smaller ones are ascribed to BSZTO. The maximum dielectric constant and loss appear with the molar ratio is 1:1 due to its more grain boundaries. Two peaks appear in the ε ∼ T curves, the peak corresponding to the lower temperature corresponds to the Curie temperature of BSZTO, while the other one is resulted by the relaxation polarization. The height of the relaxation peak decreases and the position shifts to higher temperature range with the increase of molar ratio. The maximal remanent polarization is 3.76 μC/cm2, obtained at 1 kHz when the molar ratio is 1:1. An enhanced magnetic properties are observed when the molar ratio is 1:1 due to the stronger interface interaction effect between the two phases. Strong direct magnetoelectric coupling coefficient of 1.53 V/(cm.Oe) is obtained at the field of 8000 Oe for the sample 1:4. These results may provide valuable information for improving the multiferroic properties of composite multiferroic materials. [ABSTRACT FROM AUTHOR]

• The effect of pH value of precursor solution on the microstructure and magnetoelectric properties of BaFe 12 O 19 nanoparticles and ceramics were studied. • The change of pH value of precursor solution causes large distortion of hexagonal flake grains of ceramics, which reflects the deformation of hexagonal cells in BaFe 12 O 19 crystal and leads to the asymmetry of local lattice. • The ferroelectric hysteresis loop and hysteresis loop indicate the multiferroic properties of the prepared ceramics at room temperature. The effect of ceramics leakage current on ferroelectric property were further studied. In this paper, BaFe 12 O 19 (BaM) ceramics at different pH values were prepared by sol–gel method. Effects of pH value on the microstructure, electrical as well as magnetic properties were systematically studied. XRD indicate that the ceramics were mainly BaM. However, with the pH value increasing further, the BaFe 2 O 4 impurity phase appears gradually in both powders and ceramics due to the degree of complexation between citric acid and metal cations and other reasons. SEM results show that the grain size of ceramics decreases from 2.28 μm to 1.35 μm with the pH value increase from 4 to 8. It is found that room temperature dielectric constant, residual polarization, and saturation magnetization of the ceramics is the largest when the pH value of the solution is 4, which are 0.108 μC/cm2 and 32.829 emu/g, respectively. The dielectric constant and residual polarization of ceramics decrease with the increase of pH value. The ferroelectric and magnetic hysteresis loops have confirmed room-temperature multiferroic properties of the prepared ceramics. It laid the foundation for the further development of new room temperature single-phase multi-iron materials. [ABSTRACT FROM AUTHOR]

Ba 0.85 Ca 0.15 Zr 0.1 Ti 0.9 O 3 (BCZT) ceramics were successfully synthesized by controlling the cooling rate during the sintering, and their microstructure and electrical properties were systematically analyzed. The results indicate that all BCZT ceramics show the coexistence of orthorhombic (O) and tetragonal (T) phases near room temperature. As a result of the interaction of grain size and densification, the remnant polarization, dielectric constant, and piezoelectric constant increase firstly and then decrease with the rise of cooling rate. The piezoelectric responses of BCZT ceramics are improved by optimizing the cooling process. BCZT ceramics prepared by the cooling rate with 4 °C/min have high dielectric constant (ε m = 23879), high remnant polarization (2 P r = 30.26 μC/cm2), and excellent piezoelectric responses (d 33 = 551.1 pC/N and d 33 * = 630 pm/V), which is due to the coexistence of O-T phase, larger grain size, and superior densification. These findings demonstrate that excellent piezoelectric properties for BCZT ceramics can be achieved by optimizing the cooling rate during the sintering process. • The cooling rate during sintering of BCZT ceramics has been optimized. • Enhanced piezoelectric responses were obtained by the optimization of cooling rate (4 °C/min). • Superior piezoelectricity is caused by the coexistence of O and T phase, larger grain size and excellent densification. [ABSTRACT FROM AUTHOR]

• Sr 2 Fe 1.5 Mo 0.4 Y 0.1 O 6-δ (SFMY) perovskite is synthesized as the oxygen electrode of PCECs. • SFMY perovskite shows enhanced hydration capacity and special H+/O2−/e− triple conduction. • High electrolytic activity and good operational stability have been demonstrated in the as-fabricated SFMY-based PCEC. Protonic ceramic electrolysis cells (PCECs) are emerging as potential technology to achieve efficient electrochemical hydrogen production and purification due to their high conversion efficiency and low cost. However, their maturity on a large-scale hydrogen production is notoriously hindered by the poor activity and stability of oxygen electrodes. In this work, a Sr 2 Fe 1.5 Mo 0.4 Y 0.1 O 6-δ (SFMY) oxygen electrode was designed, which shows a stable phase structure, enhanced hydration capacity, and special triple conduction (H+/O2−/e−). Electrical conductivity relaxation measurement demonstrated that SFMY showed faster H 2 O surface exchange process and improved bulk ion mobility. The as-fabricated PCEC using SFMY as the oxygen electrode can achieve a current density as high as 1570, 1235, 827, and 516 mA·cm−2 at 750 °C, 700 °C, 650 °C, and 600 °C, respectively, at a voltage of 1.3 V while displaying excellent operation stability at 700 °C during the test period of about 240 h. These results suggest that SFMY can be a potential oxygen electrode for PCECs. [ABSTRACT FROM AUTHOR]

• The PLZT@SiO 2 composite ceramic was prepared by the Stöber method, which increased the density of the ceramic, and greatly improved the energy storage density. • SEM results indicate that SiO2 weakens the crystallinity of the ceramics and restricts the grain growth of all the specimens. • Compared with the single-phase PLZT ceramics, although the electric breakdown field strength of the core-shell structure sample has not improved much, its energy storage density has increased significantly. Pb 0.925 La 0.05 Zr 0.95 Ti 0.05 @ x wt%SiO 2 (PLZT@ x wt%SiO 2 , x = 0, 1, 2, 3 and 4, marked as S0, S1, S2, S3, S4 respectively) ceramics were prepared by combining conventional sol-gel method with Stöber method, the microstructure, electrical properties and energy storage characteristics were comparatively investigated. TEM analysis prove that samples S1, S2 and S3 present core-shell structures. SEM results indicate that SiO 2 weakens the crystallinity of the ceramics and restricts the grain growth of all the specimens. When the concentration of SiO 2 is 3 wt%, the sample shows better energy storage characteristics, the value of W re of this sample can reach 2.29 J/cm3; In addition, temperature (T) will induce a phase change in the sample. When T < 50 ℃, sample S3 is ferroelectric phase, when T is in the range of 50–130 ℃, sample S3 is coexistence of anti-ferroelectric and ferroelectric phase, showing double electric hysteresis loops. In this temperature range, the temperature stability of sample S3 is the poorest, and the increases in W re density and η are 317.39 % and 25.04%, respectively. The core-shell structure samples prepared by the Stöber method can increase the energy storage density by reducing the turnover electric field. The energy storage density has increased from 0.3 J/cm3 to 2.29 J/cm3. [ABSTRACT FROM AUTHOR]

Reversible protonic ceramic cells (RPCCs) demonstrate increasingly potential for alleviating the worldwide energy crisis and environmental contamination through the efficient conversion between hydrogen and electricity. Reliable air electrode materials with high electrochemical activity and sufficient durability are imperatively desired for the commercialization process. Herein, the effort is targeted to improve electrochemical activity of Pr 2 NiO 4+δ , a traditional triple conducting oxide with inherent durability. Through introducing the highly electronegative F−, the as-designed material demonstrates improved hydratability and protonic conductivity due to the attenuated the metal-oxygen bond energy which is beneficial for the diffusion of oxygen and protonic defects. As expected, the targeted material exhibits excellent performance as the air electrode of RPCCs, i.e. a peak power density of 0.58 W cm−2 in the fuel cell mode and a current density of 2 A cm−2 at 1.3 V in an electrolysis mode at 650 °C. Eventually, the tubular RPCCs are also successfully fabricated based on this designed material and exhibit promising performance. This work offers a substantial method to design superior air electrodes for RPCCs with excellent electrochemical activity and sufficient durability. • Fluorinated Pr 2 NiO 4+δ improve the hydratability and protonic conductivity. • Highly electronegative F− attenuated the metal-oxygen bond energy. • Pr 2 NiO 3.9+δ F 0.1 exhibited high performance under electrolysis cell and fuel cell mode. • The tubular reversible proton ceramic cell has been sucessfully fabricated. [ABSTRACT FROM AUTHOR]

Ca 3 Ti 2 O 7 ceramics were prepared by a solid-state reaction process, and the influences of the sintering process on its microstructure and electric properties have been systematically studied. All the ceramic samples fabricated by different sintering processes are single polar A 2 1 am phase at room temperature, and the results indicate that the extra calcining or sintering at 1400 °C is beneficial to get the higher lattice constants. Especially the Ca 3 Ti 2 O 7 ceramics fabricated by the two-stage sintering exhibit the largest rotation angle and tilt angle of the oxygen octahedron, the densest microstructure, and the largest grain size among all the samples. The correlation of crystal structure and hybrid improper ferroelectricity confirms that the amplitude of tilt and rotation of oxygen octahedron is crucial to regulate the remnant polarization of Ca 3 Ti 2 O 7 ceramics. The leakage behaviors, dielectric and ferroelectric properties of Ca 3 Ti 2 O 7 ceramics are dependent on the microstructure, oxygen vacancy, and grain size caused by different sintering processes, and the related mechanisms have been illuminated. The highest remnant polarization (1.319 μC/cm2) to our knowledge and the lower coercive field (78.17 kV/cm) was achieved in the ceramic sample fabricated by the two-stage sintering, and these findings have an important significance in developing excellent hybrid improper ferroelectric materials. • Ca 3 Ti 2 O 7 ceramics were fabricated by a two-stage sintering. • The enhanced ferroelectric properties (P r = 1.319 μC/cm2 and E C = 78.17 kV/cm) were achieved. • The sample has the maximum distorted amplitude of oxygen octahedron and the largest grain size. [ABSTRACT FROM AUTHOR]

• Ca 3 Ti 2 O 7 ceramics were successfully synthesized by a simple tartaric acid sol-gel method. • The remarkably enhanced remnant polarization (4.32 μC/cm2) was achieved. • The sample has the larger antiferroelectric distortion displacements and the larger grain. Ca 3 Ti 2 O 7 with Ruddlesden-Popper structure is a typical hybrid improper ferroelectric with large polarization. But the room-temperature ferroelectricity of Ca 3 Ti 2 O 7 ceramics prepared by a solid-state method is not good enough. In this work, Ca 3 Ti 2 O 7 ceramics with remarkably enhanced hybrid improper ferroelectricity have been successfully fabricated by a simple tartaric acid sol-gel method. The ceramic sample exhibits the highest remnant polarization (4.32 μC/cm2) to our knowledge and lower coercive electric field (108.7 kV/cm) at room temperature. The enhanced ferroelectricity of Ca 3 Ti 2 O 7 ceramics results from the larger antiferroelectric distortion displacements and the larger grain with irregular polygon features. These findings are beneficial for developing room-temperature single phase multiferroic materials with strong magnetoelectric coupling and excellent ferroelectricity. [ABSTRACT FROM AUTHOR]

The influences of Tm3+ doping on the microstructure and electric properties of (Ba 0.85 Ca 0.15)(Zr 0.1 Ti 0.9)O 3 - x mol%Tm 2 O 3 (BCZT- x %Tm) ceramics fabricated by a solid-state method have been studied. BCZT ceramics was orthorhombic phase, and BCZT- x %Tm (x = 0.3–1) ceramics exhibited the coexistence of orthorhombic and tetragonal phases. The correlation of crystal structure and electric properties confirmed that the substitution position of Tm3+ with amphoteric characteristics was related to Tm3+ content. Especially for BCZT-0.5%Tm ceramics, the obvious amphoteric substitution for both A- and B-sites cations of Tm3+ resulted in the formation of defect dipole. The electric properties of BCZT- x %Tm ceramics were dependent on the phase structure, defects and grain size caused by the introduction of Tm3+, and the relevant defect chemical mechanism was illuminated. The enhanced piezoelectric responses (d 33 = 523 pC/N and d 33 * = 645 p.m./V) were achieved in BCZT - 0.5%Tm ceramics, and these findings have essential significance in developing high performance lead-free piezoelectric materials. [ABSTRACT FROM AUTHOR]

(1- x) BaTiO 3 - x BiFeO 3 ((1- x) BT- x BFO) (x = 0, 0.01, 0.03, 0.06, 0.1) ceramics with 0.15 wt% SiO 2 additive were synthesized by microwave sintering (MWS) and conventional sintering (CS). The crystal structure, micromorphology, dielectric relaxation behavior and ferroelectric properties of (1- x) BT- x BFO-0.15 wt% SiO 2 ceramics were investigated in detail. The results show that a phase structure transforms from a tetragonal phase to a pseudo-cubic phase for all samples and MWS method contributes to refine the grain and make the grain size more uniform. Moreover, a transition undergoes gradually from normal ferroelectric to relaxor ferroelectric is observed. The diffuseness coefficient γ of (1- x) BT- x BFO-0.15 wt% SiO 2 ceramics increases with increasing BFO content and sintered by MWS when x ≤ 0.06. The maximum diffuseness coefficient (γ = 1.69) can be obtained at x = 0.06 for MWS ceramic. Polarization-electric (P - E) hysteresis loops are gradually slimmer as x increasing, and a slimmer P - E hysteresis loops is obtained by MWS method. The remnant polarization and coercive field reduce using BFO dopant and MWS method, which also suggests that the dielectric relaxation behavior is strengthened. These results indicate that BFO dopant and MWS technique are both effective methods to improve the relaxation behavior of BT-based ceramics. • BFO dopant and MWS method both inhibit the grains growth. • BFO dopant effectively improves the relaxation behavior of BT-based ceramics. • MWS technique enhances frequency dispersion and phase diffusion behavior. • BFO dopant and MWS method could obtain slim P - E hysteresis loops. [ABSTRACT FROM AUTHOR]

Magnetoelectric composite ceramics CoFe 2 O 4 –Pb(Zr 0.52 Ti 0.48)O 3 (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 (P r) 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 (M s) and residual magnetization (M r) 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 M r and coercive field are respectively 1.67 emu/g and 404.26 Oe. • The prepared composites show bi-phase structure, the grain size is near 1 μm. • The dielectric constant shows decreasing trend with frequency. • Relaxation peaks was observed in the temperature dependence of dielectric constant. • The peak height decrease with frequency. • Antiferroelectric behavior was observed due to nonuniform domains. [ABSTRACT FROM AUTHOR]