Magnetoelectric properties of Ba0.8Sr0.2TiO3–CoFe2O4 multilayered composite film via sol–gel method

Ba_0.8Sr_0.2TiO₃–CoFe₂O₄ (BST–CFO) multilayered composite films were prepared on Pt/Ti/SiO₂/Si substrates via a sol–gel method and spin-coating technique. Microstructures, electric property, magnetic property and magnetoelectric (ME) property of the composites were studied. Results show that the composite films calcined at 750 °C have BST and CFO phases and no obvious impurity phases were detected. Further, the composite films exhibit layered structures and a transition layer which is composed of interfacial delamination exists at the interface between BST and CFO layers. Ferroelectric and ferromagnetic properties were simultaneously observed in the films, evidencing the coexistence of the ferroelectric and ferromagnetic properties. Furthermore, the saturation magnetization value of the composite film is lower than that of the pure CFO film derived by the same processing as a result of the effect of the nonferromagnetic BST layers. Also, ferroelectric hysteresis loops reveal that the saturated polarization and remanent polarization of the composite film are lower than those of the pure BST films. In addition, the composite film exhibits a strong ME effect, which makes the composite film attractive for technological applications as devices.     

Processing and magneto-electric properties of sol–gel-derived Pb(Zr0.52Ti0.48)O3–Ni0.8Zn0.2Fe2O4 2-2 type multilayered films

Pb(Zr_0.52Ti_0.48)O₃–Ni_0.8Zn_0.2Fe₂O₄ (PZT–NZFO) multilayered thin films with various volume fractions of the PZT phase (100, 74, 58, 48, 33, and 0%) were prepared on Pt/Ti/SiO₂/Si substrates using sol–gel spin-coating method. X-ray diffraction shows polycrystalline structure and scanning electron microscopy reveals good multilayer morphology of the composite thin film as annealed at 700 °C in air. The thickness of the composite films was estimated in the range of ~400 to ~600 nm. The ferroelectric and magnetic properties were measured as function of the volume fractions of the PZT phase. The magnetoelectric (ME) effect was investigated under various bias magnetic fields. The maximum ME voltage coefficient (α _E  = dE/dH) is 278 mV/cmOe for the composite film with the volume fractions of the PZT phase of ~48%.     

Effect of piezoelectric grain size on magnetoelectric coefficient of Pb(Zr0.52Ti0.48)O3–Ni0.8Zn0.2Fe2O4 particulate composites

This study investigates the variation of magnetoelectric (ME) coefficient as a function of the piezoelectric grain size in the composite system of 0.8 Pb(Zr_0.52Ti_0.48)O₃–0.2 Ni_0.8Zn_0.2Fe₂O₄. It was found that as the piezoelectric-phase grain size increases the overall resistivity, piezoelectric, dielectric, and ferroelectric property of the composite increases and saturates above 600 nm. Below 200 nm average grain size, piezoelectric and dielectric properties decrease rapidly. The ferroelectric Curie temperature was found to decrease from 377 to 356 °C as the average grain size decreases from 830 to 111 nm. ME coefficient of the composite showed a rapid change below grain size of 200 nm and was found to saturate above 600 nm to a value of 155 mV/cm.Oe.     

Microstructures and properties of Bi3.25La0.75Ti2.94V0.06O12 ferroelectric thin film deposited by sol–gel method

Bi_3.25La_0.75Ti_2.94V_0.06O₁₂ (BLTV) thin film was fabricated on the Pt/TiO₂/SiO₂/p-Si(100) substrate using sol–gel method. The microstructures and electrical properties of the film after cosubstitution of La and V were investigated. The BLTV thin film shows less highly c-axis oriented than the BIT thin film mainly with fine rod-like grains. Raman spectroscopy shows that TiO₆ (or VO₆) symmetry decreases and Ti–O (or V–O) hybridization increases for V substitution. The P _r and E _c values of the BLTV thin film are 26.3 μC/cm² and 98 kV/cm at a voltage of 12 V, respectively. The thin film also exhibits a very strong fatigue endurance up to 10¹⁰ cycles and low leakage current density. The excellent properties of the BLTV thin film are attributed to the effective decrease or suppression of oxygen vacancies after La and V cosubstitution in the thin film.     

Dielectric and magnetic properties of bulk and layered tape cast CoFe2O4–Pb(Fe1/2Ta1/2)O3 composites

The microstructure, dielectric and magnetic properties of bulk and layered CoFe₂O₄–Pb(Fe_1/2Ta_1/2)O₃ composites were studied. Ceramic samples based on previously mixed ferrite and relaxor powders were sintered at 950 °C. Ferrite and relaxor green tapes 150 μm thick were prepared by tape casting, then cut, stacked alternately, laminated and co-sintered at 950 °C. High and broad maxima of dielectric permittivity reaching 2000 at 1 kHz were found for bulk CoFe₂O₄–Pb(Fe_1/2Ta_1/2)O₃ ceramic. Measurements of the magnetization of the investigated composites as a function of magnetic field and temperature exhibited behavior typical of hard magnetic materials. The layered composites showed lower coercivity, higher saturation magnetization and a higher magnetoelectric coefficient than the bulk ceramics. Distinct changes in field- and zero field-cooled magnetization curves at −200 °C could be ascribed to the antiferromagnetic transition of the PFT relaxor phase. Multilayer CoFe₂O₄–Pb(Fe_1/2Ta_1/2)O₃ composites exhibited a magnetoelectric coefficient of 200 mV/(cm Oe) at a frequency of the modulation magnetic field equal to 5 kHz.     

Effect of gradient composite structure in cofired bilayer composites of Pb(Zr0.56Ti0.44)O3–Ni0.6Zn0.2Cu0.2Fe2O4 system on magnetoelectric coefficient

This study investigates the ferroelectric, ferromagnetic, and magnetoelectric properties of the cofired bilayer composites consisting of piezoelectric phase with formulation 0.9 Pb(Zr_0.56Ti_0.44)O₃–0.1 Pb[(Zn_0.8/3Ni_0.2/3)Nb_2/3] + 2 (mol%) MnO₂ and 40 mol% ferrite phase with formulation Ni_0.6Zn_0.2Cu_0.2Fe₂O₄ (NCZF). A bulk composite of the same composition was also synthesized for comparison. Scanning electron microscope (SEM) investigation using quadrant back scattering detector (QBSD) shows migration of ferrite phases through the interface and energy dispersive X-ray spectroscopy (EDX) analysis with X-ray mapping clarifying these as Cu-rich phases. Improved piezoelectric (d ₃₃ ~ 80 pC/N), ferroelectric (polarization of 60 μC/cm² and 0.1% strain), higher magnetization (25 emu/g) and lower coercive field (2.8 Oe) were recorded for bilayer composite. The results indicate that the gradient bilayer composites with tailored composition such that the fraction of the secondary phase is higher may lead to better magnetoelectric material.     

Multiferroic properties of multilayered BaTiO3–CoFe2O4 composites via tape casting method

Multiferroic magnetoelectric (ME) BaTiO₃–CoFe₂O₄ (BTO–CFO) ceramic composites with different thicknesses were fabricated via tape casting technique. The interfacial morphology of the composite demonstrates the presence of plate-like grains with a thickness of ~400 nm. This could be associated with the residual stresses originated from lattice mismatch and different thermal expansion coefficients between BTO and CFO layers. The dielectric constant, piezoelectric constant, and ferroelectric properties of the multilayered composite are degraded in the presence of CFO layers in comparison with those of BTO bulk. Furthermore, the dielectric constant and polarization of the composite decrease with increasing frequency. The leakage current density and magnetic remanence ratio of the composite reach up to the order of 10^?6 A/cm² and 40 %, respectively. The direct and converse ME coefficients were measured to be 8.1 μV/cm Oe and 1.1 × 10^?3 G/V, respectively. Based on the converse ME effect, an electrically controlled ME inductor was designed using the composite as its core. The inductance and tunability of the inductor increase with increase of applied dc electric field.     

Synthesis of nanocrystalline LaFeO3 powders via glucose sol–gel route

LaFeO₃ were prepared by sol–gel process using glucose as a complexing agent. Thermogravimetric (TG), differential thermal analysis (DTA), Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), Field emission scanning electron microscope (FSEM) and Transmission electron microscope (TEM) techniques were used to characterize precursor and derived oxide powders. The effect of the mol ratios of glucose to metal ions (glucose/M) on the formation of LaFeO₃ was investigated. XRD analysis showed that single-phase and well-crystallized LaFeO₃ was obtained from precursor with glucose/M = 3:5 and 3:10 at 500 °C. LaFeO₃ nanoparticles with a diameter of about 30 nm were obtained. However, for precursor with glucose/M = 3:20, pure LaFeO₃ was not obtained at temperature below 600 °C.     

Thickness-dependent electrical properties of sol–gel derived Pb(Zr0.52Ti0.48)O3 thick films using PbTiO3 buffer layers

Pb(Zr_0.52Ti_0.48)O₃ (PZT) thick films, with thickness up to 4 μm, using PbTiO₃ (PT) buffer layers were successfully prepared on silicon-based substrates by a sol–gel method. Thermal analysis (thermogravimetric–differential thermal analysis) of PT and PZT sols were used to determine the pyrolysis and annealing temperatures. X-ray diffraction results show that the PZT/PT composite thick films possess perovskite structure and the dominant crystalline orientation changes from (100) to (110) with increasing the film thickness. Furthermore, the composite thick films exhibit thickness-dependent ferroelectric and dielectric properties, i.e., the coercive field decreases while dielectric constant increases as the thickness increases. Theoretical analysis shows that the thickness-dependent electrical properties are mainly attributed to the low dielectric constant of PT buffer layer and the relaxation of internal stress in PZT films.     

CoFe2与CoFe2O4质量比及MgO稀释对CoFe2@CoFe2O4磁性的影响

采用金属有机盐热分解方法制备了MgO包覆的CoFe₂O₄纳米粒子（CoFe₂O₄@MgO）,然后将CoFe₂O₄@MgO在H₂中还原,接着在空气中氧化制备了一组CoFe₂@CoFe₂O₄@MgO样品;用盐酸溶液溶解CoFe₂@CoFe₂O₄@MgO中的MgO获得另一组样品（CoFe₂@CoF₂O₄）。测量并绘制了CoFe₂@CoFe₂O₄@MgO和CoFe₂@CoF₂O₄的磁化强度随外磁场及温度变化的关系曲线。随着氧化温度升高,CoFe₂@CoFe₂O₄@MgO和CoFe₂@CoF₂O₄的矫顽力H_c、饱和磁化强度M_s、剩磁比M_r/M_s及磁有序状态发生显著变化,这些变化强烈依赖于磁性粒子的各向异性及粒子间的偶极相互作用。     

Preparation and magnetic properties of SrFe12O19/Ni0.5Zn0.5Fe2O4 nanocomposite ferrite microfibers via sol–gel process

SrFe₁₂O₁₉/Ni_0.5Zn_0.5Fe₂O₄ nanocomposite ferrite microfibers with diameters of 1–2 μm have been prepared by the sol–gel process. The SrFe₁₂O₁₉/Ni_0.5Zn_0.5Fe₂O₄ nanocomposite ferrites are formed after the precursor calcined at 850 °C for 2 h, fabricating from nanosized particles with a uniform phase distribution. The ferrite grain size increases with the calcination temperature. The magnetic properties for the nanocomposite ferrite microfibers are mainly influenced by the chemical composition and grain size. The nanocomposite ferrite microfibers obtained at 900 °C show the enhanced specific saturation magnetization (M_sh) of 64.8 Am² kg⁻¹, coercivity (H_c) of 146.5 kA m⁻¹ and remanence (M_r) of 33.6 Am² kg⁻¹ owing to the exchange–coupling interaction. This exchange–coupling interaction in the SrFe₁₂O₁₉/Ni_0.5Zn_0.5Fe₂O₄ nanocomposite ferrite microfibers has been discussed.     

Magnetoelectric and electrical properties of WO3-doped (Ni0.8Zn0.1Cu0.1)Fe2O4/[Pb(Ni1/3Nb2/3)O3–Pb(Zn1/3Nb2/3)O3–PbTiO3] composites

A total of 5 mol% WO₃-doped (1−x)(Ni_0.8Zn_0.1Cu_0.1)Fe₂O₄/xPb(Ni_1/3Nb_2/3)O₃–Pb(Zn_1/3Nb_2/3)O₃–PbTiO₃ ((1−x)NZCF/xPNN-PZN-PT) magnetoelectric particulate ceramic composites were prepared by conventional solid-state reaction method via low-temperature sintering process. X-ray diffraction (XRD) measurement and scanning electron microscopy (SEM) observation indicate that piezoelectric phase and ferrite phase coexist in the sintered particulate ceramic composites. Dielectric property of the (1−x)NZCF/x0.53PNN–0.02PZN–0.05Pb(Ni_1/2W_1/2)O₃–0.40PT ((1−x)NZCF/xPNN-PZN-PNW-PT, nominal composition) composites is improved greatly as compared to that of the undoped (1−x)NZCF/xPNN-PZN-PT composites. The WO₃-doped (1−x)NZCF/xPNN-PZN-PT composites exhibit typical P–E hysteresis loops at room temperature accompanied by the decrease of saturation polarization (P _s) and remnant polarization (P _r). At the same time, piezoelectric property of the composites deteriorates greatly with the increase of ferrite content. The (1−x)NZCF/xPNN-PZN-PNW-PT composites can be electrically and magnetically poled and exhibit apparent magnetoelectric (ME) effect. A maximum ME voltage coefficient of 13.1 mV/(cm Oe) is obtained in the 0.1NZCF/0.9PNN-PZN-PNW-PT composite at 400 Oe d.c. magnetic bias field superimposed 1 kHz a.c. magnetic field with 5 Oe amplitude. The addition of WO₃ in the piezoelectric phase decreases sintering temperature greatly from 1180 °C to 950 °C and decreases dielectric loss sharply of the composites, thus the ME voltage coefficient increases. Such ceramic processing is valuable for the preparation of magnetoelectric particulate ceramic composites with excellent ME effect.     

Characterization of Li2MnSiO4 and Li2FeSiO4 cathode materials synthesized via a citric acid assisted sol–gel method

Two members of the family of orthosilicate, Li₂FeSiO₄ and Li₂MnSiO₄, are prepared by a citric acid assisted sol–gel method. As cathode materials for lithium-ion batteries, their structural, morphological and electrochemical characteristics are investigated and compared. Both cathode materials have nanoparticles with similar lattice parameters. Li₂FeSiO₄ has a maximum discharge capacity of 152.8 mAh g⁻¹, and 98.3% of its maximum discharge capacity is retained after fifty cycles. However, the discharge capacity of Li₂MnSiO₄ fades rapidly and stabilized at about 70 mAh g⁻¹ after twenty cycles. The electrochemical impedance and differential capacity analysis indicate that Li₂MnSiO₄ has larger charge transfer impedance and higher electrochemical irreversibility than Li₂FeSiO₄, which makes its electrochemical behaviors seriously deteriorate and leads to difference between two silicate materials.     

Synthesis and electrical properties of Pb(Zr0.52Ti0.48)O3 thick films embedded with ZnO nanoneedles prepared by the hybrid sol–gel method

Pb(Zr_0.52Ti_0.48)O₃ thick films embedded with ZnO nanoneedles (PZT–ZnO_n) were successfully prepared on Pt/Cr/SiO₂/Si substrates by the hybrid sol–gel method via spin-coating ZnO_n suspension and lead zirconate titanate (PZT) sol. To control the orientation of the films, a PbTiO₃ (PT) layer was first deposited as a seed layer. Effects of annealing method and ZnO_n contents on the corresponding orientation and crystallization of PZT–ZnO_n films were investigated by XRD and SEM. The results show that all the PZT–ZnO_n composite thick films have pure perovskite structure and high-quality film surface. The dielectric and ferroelectric properties of the PZT–ZnO_n films are close to the PZT films, and have a little decrease with the increasing of the ZnO_n contents.     

Synthesis and properties of magnetic solid superacid: SO4/ZrO2–B2O3–Fe3O4

A magnetic SO₄²⁻/ZrO₂–B₂O₃–Fe₃O₄ solid superacid catalyst is prepared via a simple chemical co-precipitation approach. The obtained materials were characterized in detailed by X-ray powder diffraction, thermogravimetric analysis–different scanning calorimetry, Fourier transform infrared spectroscopy (FTIR), electron microscopy (SEM and TEM), and Mossbauer spectra. Powder X-ray diffraction patterns show that in this composite oxide the transformation temperature of ZrO₂ from tetragonal to monoclinic phase is higher compared to the pristine SO₄²⁻/ZrO₂ material. The introduction of Fe₃O₄ endows the superacid with a super-paramagnetic property while in a ferromagnetic state after calcination. The superacid exhibits high catalytic activity in forming ethyl acetate by esterification.     

Black nanocrystalline cubic zirconia: Manganese-stabilized c-ZrO2 prepared via the sol–gel method

Nanostructured manganese-stabilized cubic zirconia (MnSZ) powders, solid solutions of Zr_1−xMn_xO_2−yx = 0, 0.03, 0.06 and 0.09, were obtained via the sol–gel method. The doped phases crystallized at 500 °C into black cubic nanocrystalline zirconia.     

The morphotropic phase boundary and electrical properties of (1?? x )Pb(Zn1/2W1/2)O3– x Pb(Zr0.5Ti0.5)O3 ceramics

Ceramics in the solid solution of (1 − x)Pb(Zn_1/2W_1/2)O₃–xPb(Zr_0.5Ti_0.5)O₃ system, with x = 0.80, 0.85, 0.90, and 0.95, were synthesized with the solid-state reaction technique. The perovskite phase formation in the sintered ceramics was analyzed with X-ray diffraction. It shows that the rhombohedral and the tetragonal phases coexist in the ceramic with x = 0.90, indicating the morphotropic phase boundary (MPB) within this pseudo-binary system. Dielectric and ferroelectric properties measurements indicate that the transition temperature decreases while the remanent polarization increases with the addition of Pb(Zn_1/2W_1/2)O₃. In the composition of x = 0.85 which is close to the MPB in the rhombohedral side, a high piezoelectric property with d ₃₃ = 222 pC/N was observed.     

Densification and dielectric properties of SrO–Al2O3–B2O3 ceramic bodies

The influence of SrO (0·0–5·0 wt%) on partial substitution of alpha alumina (corundum) in ceramic composition (95 Al₂O₃–5B₂O₃) have been studied by co-precipitated process and their phase composition, microstructure, microchemistry and microwave dielectric properties were studied. Phase composition was revealed by XRD, while microstructure and microchemistry were investigated by electron-probe microanalysis (EPMA). The dielectric properties by means of dielectric constant (ε _r ), quality factor (Q × f) and temperature coefficient of resonant frequency (τ _f ) were measured in the microwave frequency region using a network analyser by the resonance method. The addition of B₂O₃ and SrO significantly reduced the sintering temperature of alumina ceramic bodies to 1600 °C with optimum density (∼ 4g/cm³) as compared with pure alumina powders recycled from Al dross (3·55g/cm³ sintered at 1700 °C).     

An investigation of V2O5/polypyrrole composite cathode materials for lithium-ion batteries synthesized by sol–gel

A lamellar compound of V₂O₅ was prepared by a simple sol–gel method using H₂O₂ and V₂O₅ as starting materials. The composites of V₂O₅/PPy (polypyrrole) were synthesized by in situ polymerization, and characterized by thermogravimetric analysis (TGA), scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectrum, and X-ray diffraction (XRD). The electrochemical properties of the composites were investigated with galvanostatic charge–discharge test, cyclic voltammetry and A.C. impedance techniques. The results show that pyrrole was uniformly polymerized around the V₂O₅, and the V₂O₅/PPy composite possessed excellent electrochemical performance. The specific discharge capacity of the 2.5% mass percent PPy composites (271.8 mAh g⁻¹) was higher than that of pure V₂O₅ (247.6 mAh g⁻¹) at 0.1C rate and it has the voltage limits of 1.8–4.0 V. Furthermore, the specific discharge capacity remained at 225.4 mAh g⁻¹ after 50 cycles. The chemical diffusion coefficient D_Li⁺$D_{{\text{Li}}^{+}}$ values were calculated, depending on x-values in Li_x+1.1V₂O₅. The values of D_Li⁺$D_{{\text{Li}}^{+}}$ range from 2.18 × 10⁻¹² cm² s⁻¹ to 4.5 × 10⁻¹⁴ cm² s⁻¹ for V₂O₅/PPy composite, and it decreased as the amount of intercalated Li⁺ increased.