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Relaxor ferroelectric ceramics (1–x)Pb(Mg1/3Nb2/3)O3–xPbTiO3 (PMN–PT) at the morphotropic phase boundary exhibit high piezoelectric and electromechanical performances. In this study, translucent 0.67PMN–0.33PT piezoelectric ceramics with various Ce doping concentrations (0, 1, 2, 2.5, and 3 mol%) were fabricated using a two-step synthesis method. All ceramics exhibited a high relative density (> 97%). The valence of Ce ions in PMN–PT ceramics and their influence on the piezoelectric, ferroelectric, dielectric, strain behavior, and luminescence properties of PMN–PT ceramics were investigated. A maximum d33 of 800 pC/N was obtained when the doping amount of Ce was 2 mol%. The maximum dielectric constant and corresponding temperature Tm decreased with the increase of Ce doping concentration, and all the dielectric loss factors were lower than 0.15. X-ray photoelectron spectroscopy revealed that Ce3+ and Ce4+ coexist in PMN–PT ceramics, and Ce3+ is dominant with a low Ce doping content, which enhances the luminous intensity of Pb2+ ions.

We studied the fracture strain of polycrystal ɑ-iron at three different hydrogen concentrations and for three crystal sizes with molecular dynamics simulations (MDs). As the hydrogen concentration increases, a fine crystal model's fracture resistance is prone to below a comparatively coarse grain model. This finding elucidates that the most vulnerable area can alter from coarse grain zone to fine-grain zone in the welding heat-affected zone (HAZ) with the effect of hydrogen. A simplified model is thus built to predict the strain energy increment in different crystal size systems caused by the introduction of hydrogen atoms. This strain energy increment is not equal to the fracture energy reduction induced by the same amount of hydrogen insertion, demonstrating that elastic volume expansion of grain boundary (GB) caused by hydrogen is not the determining mechanism of intergranular failure. The density of triple or multi-junctions of GBs, which is typically dependent on the volume fraction of GBs, is the crucial factor for intergranular failure caused by hydrogen embrittlement.

The materials processing history has a great influence on their properties and finally determines their application effect. In this paper, the ferroelectric, polarization-switching current, and strain properties of Mn-doped 0.75Pb(Mg1/3Nb2/3)O3-0.25PbTiO3 ceramics were studied in fresh state, aged state, and poled state, respectively. Compared with the symmetric polarization-electric-field (P-E) hysteresis loops, current-density-electric-field (J-E) curves, and bipolar electric-field-induced strain (S-E) curves in fresh state samples, asymmetric P-E loops, J-E curves, and bipolar S-E curves were obtained in poled state samples. Well-aged-state samples exhibit double hysteresis P-E loop, four peaks J-E curves, and symmetric S-E curves without negative strain. The symmetry-conforming short-range order (SC-SRO) principle of point defects and internal electric field Ei is employed to clarify the different phenomenon of three states. Results indicated that randomly oriented defect polarization PD in aged samples can reverse the spontaneous polarization PS back and result in the double hysteresis P-E loop and four peaks J-E curves. The oriented PD and resulting Ei in poled-state samples will lead to the asymmetric loops and strain memory effect.

To investigate the effect of hydrogen atoms on the size of the plastic deformation zone, molecular dynamics (MD) simulations were performed on a single crack model. The model uses pre-charged hydrogen to quantify the compression effect of hydrogen atoms on the plastic zone during cyclic loading. The results show that stress release at the crack tip occurs mainly in the form of plastic deformation, and the degree of compression in the plastic zone increases with increasing hydrogen concentration. A compression factor, which considers hydrogen concentration, is found with the help of the simulation results. A modified fatigue crack growth rate (FCGR) model, combined with the compression factor, was then used to predict the hydrogen-assisted fatigue crack growth rate. The proposed model shows excellent agreement with the experimental data for X100 steel, and it provides a new framework to describe hydrogen-assisted cracking.

Bi5Ti3FeO15 (pentabismuth trititanium iron pentadecaoxide), which is a multiferroic four-layer Aurivillius phase compound, has received much attention in recent years. However, three mutually inconsistent orthorhombic space groups, i.e. A21 am, Fmm2 and Pnn2, have been reported for the room-temperature phase of Bi5Ti3FeO15 by X-ray and neutron diffraction investigations. Here, electron diffraction results are presented and discussed for the first time to unambiguously clarify the room-temperature space group of ceramic Bi5Ti3FeO15. It has been found that all the observed reflections from the ceramic agree with those expected in A21 am, while the observed reflections 011, 013 and 015 should be forbidden in the case of Fmm2, and no 107 and 109 reflections were observed although allowed for Pnn2. The present study has demonstrated that the space group of Bi5Ti3FeO15 ceramic is A21 am rather than Fmm2 or Pnn2, an identification that proved to be a challenge for X-ray diffraction. On the basis of the space group A21 am, the lattice parameters of the Bi5Ti3FeO15 ceramic were calculated from its X-ray diffraction data.

Domain structures and their reversal process of (010)-cut Pb(Mg1/3Nb2/3)O3–38%PbTiO3 single crystal were in situ investigated under varying electric fields by polarized light microscope. High-density needlelike ferroelectric microdomains were observed in macrodomains. When an electric field along [101] was applied on the crystal, macrodomain walls keep immobility, while the vertical microdomains first flip to the transverse direction and then to the vertical direction again. The two-step 90° domain reversal exhibits quite different characteristics. The first step finished quickly at a low electric field and in a narrow electric field range, leading to high polarization current. The second step happened slowly at the high electric field and in a wide electric field range, and no obvious polarization current was observed. Two-step domain reversal mechanism was investigated, and our findings will help in understanding the excellent properties of relaxor Pb(Mg1/3Nb2/3)O3–PbTiO3 single crystal.

Submicron Bi₂Fe₄O9 crystals were successfully synthesized by a one-step hydrothermal synthesis method and employed effectively as a visible-light-driven photocatalyst for the degradation of methylene blue dye. Scanning electron microscopy and transmission electron microscopy observations revealed that the as-prepared sample consisted mainly of submicron plates and a small quantity of submicron particles. The ultraviolet-visible absorption spectrum of the submicron Bi₂Fe₄O9 crystals shows two broad absorption edges in the visible region with band gaps of 1.57 and 2.15 eV, respectively. The photodegradation rate of Bi₂Fe₄O9 is more than twice that of TiO₂ for the degradation of methylene blue under visible-light irradiation, demonstrating the excellent photocatalytic activity of these submicron Bi₂Fe₄O9 crystals. The acquired photocurrent densities are 43.3 and 46.6 μA/cm² for visible-light and ultraviolet-visible irradiation, respectively. These results demonstrate that the submicron Bi₂Fe₄O9 crystals are potential visible-light photocatalysts for use in environmental purification and solar energy utilization.

Electrocaloric effect (ECE) offers a promising method for highly efficient and environment-friendly solid-state refrigeration. To obtain giant EC temperature change (ΔT), high electric field and temperature are usually applied to ECE materials, but few investigations have been done on the influence of Joule heating on ECE caused by leakage current at high electric field and temperature. In this paper, ECE, leakage current and Joule heating of 0.5Ba(Zr0.2Ti0.8)O3-0.5(Ba0.7Ca0.3)TiO3 (0.5BZT-0.5BCT) ceramic were studied in the wide electric field and temperature range. The distortion of ECE curves at high electric field and temperature is proved to be caused by Joule heating which makes a negative effect on ECE refrigeration. The effective temperature change (ΔTeff) was defined, and the difference among ΔTeff, EC temperature change measured directly (ΔTD), and the intrinsic EC temperature change (ΔTECE) was discussed in detail. The results provide a guiding significance to the investigation of ECE and electronic materials.

Bi4LaTi3FeO15 (BLTF) multiferroic ceramics of four-layered Aurivillius structure were successfully synthesized by hot-press sintering via inserting magnetic LaFeO3 into ferroelectric Bi4Ti3O12 matrix. The BLTF ceramics are very dense and consist mainly of plate-like grains. The ceramics show saturated ferroelectric loops with a remanent polarization 2Pr of 32.3 µC/cm2 and a coercive field 2Ec of 188 kV/cm. Their permittivity and dissipation factor are about 245 and 0.0228 at 100 kHz. The leakage current density is 1.6 × 10−5 A/cm2 at the applied electric field of 170 kV/cm. The room temperature saturation magnetization value of the BLTF ceramics is about 0.088 emu/g. Compared to the BLTF ceramics prepared by pressureless sintering, the ferroelectric, dielectric and magnetic properties of the present BLTF ceramics are enhanced obviously. This work gives a new pathway for synthesing high-performance room-temperature multiferroic ceramics.

The temperature and electric field dependences of electrocaloric effect (ECE) of 0.5 mol.% La–doped 0.88Pb(Mg 1/3 Nb 2/3 )O 3 –0.12PbTiO 3 (La–doped 0.88PMN–0.12PT) relaxor ferroelectric ceramic were investigated by direct measurement method using a home–made adiabatic calorimeter. Direct and indirect ECE were compared and large discrepancy was observed not only in a magnitude but also in the changing trend. Dual–peak effect was observed in the ΔT ECE –T curves, which can be ascribed to the evolution of polar nanoregions (PNRs). The first ECE peak appears near the depolarization temperature (T d ) of 40 °C at low electric field, and the second ECE maxima with ΔT ECE of 0.44 °C at E = 4 kV/mm occurs at a higher temperature around 70 °C corresponding to the temperature with the maximum dielectric constant (T m ). In addition, the ECE was found to insignificantly change well above the T m . The wide temperature range accompanied by high ΔT ECE in La–doped PMN–0.12PT ferroelectric ceramic indicates the promising candidate for applications in cooling technologies.

La-doped 0.75Pb(Mg1/3Nb2/3)O3–0.25PbTiO3 (PMN–PT) transparent ceramics were fabricated by uniaxial hot-pressing sintering, oxygen atmosphere sintering and two-stage sintering technology, respectively. PMN–PT ceramics fabricated by two-stage sintering method show the best densification and highest transparency. Its optical transmittance reaches to 70% at 900 nm which is very close to its theoretical transmittance 71%. The temperature dependent dielectric properties and P–E hysteresis loops of these three ceramics show that they all exhibit relaxor characteristics. Effects of sintering methods on the dielectric and ferroelectric properties, diffusivity coefficient, and polarization current density were investigated.

Random-oriented 0.5LaFeO3-Bi4Ti3O12 thin films were prepared via a sol–gel method on (111)Pt/Ti/SiO2/Si(100) substrates. According to X-ray diffraction analysis, the films have a single-phase Aurivillius perovskite structure with a space group Fmm2. As expected, the coexistence of ferroelectric and ferromagnetic properties was detected at room temperature. The remanent polarization (2Pr) and the saturated magnetization (Ms) are 61.94 μC/cm2 and ∼0.90 emu/cm3, respectively. Furthermore, a magneto-dielectric effect was demonstrated at room temperature with a magneto-dielectric coefficient of 0.67% under a low magnetic field of 0.25 T, probably resulting from the charge ordering of Fe2+ and Fe3+. Finally, a dielectric relaxation behavior was observed around 130 K, which is also related to the coexistence of Fe2+ and Fe3+.

Polycrystalline Bi4LaFe0.5Co0.5Ti3O15 (BLFCTO) thin films were prepared on (111)Pt/Ti/SiO2/Si via a sol–gel process. The films have a single-phase four-layered Aurivillius structure with space group Fmm2. As expected, the BLFCTO films present room-temperature multiferroic properties with a remanent polarization 2P r of ~42 μC cm−2 and a saturated magnetization M s of ~7.2 emu cm−3. More interestingly, both dielectric relaxation behavior and room-temperature magneto-dielectric effect were observed in the BLFCTO films, probably resulting from the charge ordering of Fe2+ and Fe3+. The magneto-dielectric coefficient of ~3.8% was obtained at room temperature under a low magnetic field of 0.5 T.

Single-phase Bi5Ti3FeO15 (BTFO) ceramics were synthesized by hot-pressing sintering process using sol-gel derived fine powders. X-ray diffraction indicates that the ceramics have expected four-layered Aurivillius structure with an orthorhombic symmetry. The ceramics are very dense and consist of plate-like grains. The BTFO ceramics exhibit typical ferroelectric hysteresis loops with a remnant polarization 2Pr of 14.1 µC/cm2 and a coercive field 2Ec of 142 kV/cm. Their dielectric constant and dissipation factor at 100 kHz are about 152.8 and 0.007, respectively. The remanent magnetization 2Mr of the BTFO ceramics is about 3.0 memu/g at room temperature. Both the dielectric loss and magnetic properties of the present BTFO ceramics are enhanced compared to those for pressureless sintered BTFO ceramics. This work provides a flexible way to fabricate high-performance multiferroic ceramics at room temperature.

Polycrystalline Bi 4 YFeTi 3 O 15 thin films were prepared on (111)Pt/Ti/SiO 2 /Si through a sol-gel process. X-ray diffraction analysis shows the films have a single-phase four-layered Aurivillius structure with the space group of Fmm 2. As expected, the Bi 4 YFeTi 3 O 15 films exhibit the coexistence of ferroelectric and weak ferromagnetic properties with the remanent polarization (2 P r ) ∼ 53.62 μC/cm 2 and the saturated magnetization ( M s ) ∼ 0.50 emu/cm 3 at room temperature. More interestingly, both dielectric relaxation behavior and room-temperature magneto-dielectric effect were observed in the Bi 4 YFeTi 3 O 15 films, probably resulting from the coexistence of Fe 2+ and Fe 3+ . The conduction mechanism of the films from 10 to 300 kV/cm is dominated by Ohmic mechanism, space-charge-limited current (SCLC), and trap-filled-limit (TFL) current, respectively. The leakage current density remains lower than 1.03 × 10 −5 A/cm 2 under the poling field below 300 kV/cm at 300 K.

Exchange-biased GMR sensors were employed for biodetection using a DC in-plane measuring method and a magnetic label of Fe 3 O 4 microspheres. It was revealed that an ultra-wide concentration span covering five orders from 10 ng/mL to 1000 μg/mL was achieved in a home-made biodetection device. The concentration x dependence of output voltage difference |Δ V | between with and without magnetic labels, exhibits nonlinear futures, which undergoes two functions depending on the concentration region. For the low concentration region from 10 ng/mL to 10 μg/mL, a logarithmic relation of |Δ V |=26.3lg x +91.4 fits well, while for the high concentration region, a negative exponential function of |Δ V |=3113(1−e − x /250 ) describes the |Δ V |~ x relation better. For the former, the “coffee ring” effect, formed during the solvent evaporation, was considered as the main reason for the nonlinear relation. While for the latter with high concentration, the overlap among the particles and the enhanced interaction of the magnetic dipole were responsible for the nonlinear |Δ V |~ x relationship. Moreover, the calculated detectable concentration limit is agreed well with the experimental data.

Microwave soft magnetic films (SMFs) are key materials, which can effectively miniaturize and multifunctionalize the electromagnetic components and devices, such as filters, phase shifters, thin film wireless inductors, magnetic recording write heads, antennas, etc.1, and reduce their occupation area in microwave monolithic integrated circuit (MMIC) boards. Modern electronic products are heading towards high density, high-frequency, frequency tunability, lightweight and low energy consumption, etc., which give rise to increasing demands for microwave SMFs. Microwave SMFs should have higher ferromagnetic resonance frequency (f FMR ), high permeability, and are to be fabricated in an IC compatible process. Metallic soft magnetic films exhibit special advantages in MMIC devices since they have higher 4πM S and permeability, and good compatibility with the IC fabrication process. Therefore, self-biased metallic SMFs prepared at IC compatible process have drawn an increasing attention2.

In the ferroelectric Bi4Ti3O12, the major component P s(a) of spontaneous polarization P s lies along the a axis; the component P s(c) along the c axis is small. The two switchable components are expected to make up various types of domain walls (DWs). According to group-theory analysis, 11 permissible types of DWs are predicted to exist theoretically, and they include five types of ferroelectric DWs, one type of anti-phase boundary (APB) and five types of APB-combined ferroelectric DWs. The five types of ferroelectric DWs are P s(a)-90° DWs, P s(a)-180° DWs, P s(c)-180° DWs, P s(a)-90°/P s(c)-180° DWs and P s-180° DWs. In Bi4Ti3O12 single crystals, just the five types of ferroelectric DWs were observed using transmission electron microscopy, with no trace of APBs or APB-combined ferroelectric DWs seen. The P s(a)-90° domains are lamellar and do not have even thickness. Both the P s(a)-90° DWs and P s(a)-90°/P s(c)-180° DWs lie mainly on the (110) plane, but often fold to the (001) plane. The P s(a)-180° domains are predominantly flaky. Both the P s(a)-180° DWs and P s-180° DWs lie mainly on the (001) plane. The P s(c)-180° DWs observed are irregularly curved.

Soft magnetic films (SMFs) are key materials for miniaturization and multifunctionality of radio frequency and microwave components and integrated circuits (ICs) due to the good high-frequency soft magnetic performances and the compatibility to IC processing technologies. Magnetic micro-inductors are one of widely used microwave IC components. The SMFs in magnetic micro-inductors should have a well-defined in-plane uniaxial magnetic anisotropy in order to reach a high ferromagnetic resonance frequency f FMR . On the other hand, a high permeability is only available when excitation magnetic field being along the magnetic hard-axis (HA) direction, i.e. HA excitation. However, the typical planar micro-inductors are round or square, the magnetic anisotorpy characterisitics of the SMFs above indicates that the efficiency of SMFs can only reach 50% in inductors. Although many attempts have been made to enhance the efficiency of SMFs in inductors,1 100% HA excitation is still difficult to be reached.

Dense relaxor ferroelectric 0.88Pb(Mg1/3Nb2/3)O3–0.12PbTiO3 (0.88PMN–0.12PT) ceramics with different La-doping contents (0, 1, 2 and 4 at.%) were sintered by using powders synthesized via a solid-state reaction route. The effects of La doping on the microstructures and electric properties of the 0.88PMN–0.12PT ceramics were investigated. It was found that the average grain size, remanent polarization Pr, coercive field Ec, Curie temperature Tc and leakage-current density J of the ferroelectric ceramics decrease significantly with increasing La doping content. The decrease in Pr, Ec and Tc can be understood in term of the fact that the substitution of Pb2+ ions by La3+ ions suppresses the long-range coupling of BO6 octahedrons, while the abatement in J can be explained according to the reduction of oxygen vacancies caused by La doping. By fitting the J–E curves, the conduction mechanism of the 0.88PMN–0.12PT ceramics is confirmed to be Ohmic conduction generated from oxygen vacancies. The dielectric and ferroelectric properties of 0.88PMN–0.12PT ceramics are tunable with manipulating the La doping content.

0.67Pb(Mg1/3Nb2/3)O3–0.33PbTiO3 (PMNT) ceramics were fabricated by using their powders synthesized through a sol–gel process. Excess Pb(CH3COO)2·3H2O (0, 2, 5, 10 or 15 mol%) was added to the starting materials to study the effect of excess Pb on the microstructures, ferroelectric and dielectric properties of the PMNT ceramics. All the X-ray diffraction peaks can be indexed using perovskite-type PMNT for the ceramics prepared with excess Pb, while the PMNT ceramics with no excess Pb contain a little pyrochlore phase. The PMNT ceramics prepared with 2 mol% excess Pb are dense and uniform and composed of grains ranging from 3 to 7 μm. They exhibit the largest remnant polarization (P r = 32.1 μC/cm2) and the highest peak dielectric constant (e max = 12,725). When more than 2 mol% excess Pb added, the electrical properties of the PMNT ceramics decreased with increasing excess Pb. Too much excess Pb (over 10 mol%) resulted in abnormal grain growth (>20 μm), large pores and residual PbO in amorphous state in PMNT ceramics, and they impaired the ferroelectric and dielectric properties of PMNT ceramics greatly.

Perovskite-type 0.67Pb(Mg1/3Nb2/3)O3-0.33PbTiO3 (PMNT) powders were fabricated by using a sol–gel process. Excess Pb(CH3COO)2·3H2O (0, 2, 5, 10 or 15 mol%) was added to starting materials to compensate PbO loss from volatilization during heat treatment. X-ray diffraction (XRD) was employed to investigate the effect of excess Pb on the perovksite phase formation of the PMNT powders. It was found that the optimal level of the excess Pb content is 5 mol%. When the raw materials contained 5 mol% excess Pb, the PMNT powders of purest perovskite form was obtained at the calcination temperature of 850 °C. In the PMNT powders, most part of the intermediate phase was Pb-rich pyrochlore Pb2Nb2O7 which was transformed into perovskite phase after calcination at 650 °C, while the residual pyrochlore phase was Pb-deficient Pb3Nb4O13 which required calcination at a higher temperature (650–850 °C) to transform into perovskite phase. Compared with the conventional solid-state reaction methods and the solution-based methods reported previously, the present sol–gel route is better at synthesizing PMNT powders of perovskite phase at a low temperature.

Recently, ferroelectric tunnel junctions (FTJs) have attracted great attention due to promising applications in non-volatile memories. In this study, we report high-temperature tunneling electroresistance (TER) of metal/ferroelectric/semiconductor FTJs. Hysteretic resistance-voltage loops are observed in the Pt/BaTiO3/Nb:SrTiO3 tunnel junction from 300 to 513 K due to the modulation of interfacial Schottky barrier by polarization switching in the 4 u.c.-thick BaTiO3 barrier via a ferroelectric field effect. The Pt/BaTiO3/Nb:SrTiO3 device exhibits a giant ROFF/RON resistance ratio of ∼3 × 105 at 383 K and maintains bipolar resistance switching up to 513 K, suggesting excellent thermal endurance of the FTJs. The temperature-dependent TER behaviors are discussed in terms of the decrease of polarization in the BaTiO3 barrier, and the associated junction barrier profiles are deduced by transport and capacitance analyses. In addition, by extrapolating the retention time at elevated temperature in an Arrhenius-t...

A Fe0.7Co0.3-B multilayer was laminated by three Fe0.7Co0.3-B ferromagnetic sublayers prepared by composition gradient sputtering. Three Fe0.7Co0.3-B ferromagnetic sublayers have their individual directions of uniaxial magnetic anisotropy, and the easy magnetic axis of neighboring sublayer successively rotates 60° in the film plane. It is exciting that a quasi magnetic isotropy was achieved in the designed multilayer with a quasi-isotropic hysteresis loop and quasi-isotorpic ferromagnetic resonance around 3.7 GHz. This omnidirectional multilayer is promising for the application in inductors since the 100% hard-axis excitation is achieved for any shaped inductors.

Strong converse magnetoelectric coupling was observed in a multiferroic heterostructure of Fe59.3Co28.0Hf12.7 film on (011) cut lead zinc niobate-lead titanate (PZN-PT) slab, which exhibited a large electric field (E-field) tunability of microwave magnetic properties. With the increase of E-field from 0 to 6 kV/cm on PZN-PT, the ferromagnetic resonance (FMR) field Hr shifts downwards by 430.7 Oe along [011¯] direction and upwards by 492.9 Oe along [100] direction of the PZN-PT. Accordingly, the strong magnetoelectric coupling led to a significantly enhanced self-biased FMR frequency from 4.2 to 7.9 GHz under zero bias magnetic field, and the magnetic damping constant α was decreased from 0.0260 to 0.0185 at the same time. These features demonstrate that this multiferroic laminate is promising in fabrication of E-field tunable microwave components.