Room temperature multiferroicity in Aurivillius compounds Bi6Fe2−xNixTi3O18 (0≤x≤1)

We investigate the structural, magnetic, ferroelectric, and dielectric properties of Bi₆Fe_2−xNi_xTi₃O₁₈ (0≤x≤1). The coexistence of ferroelectricity and ferromagnetism were observed at room temperature for the Ni-doped samples. The ferromagnetism in Bi₆Fe_2−xNi_xTi₃O₁₈ can be understood in terms of spin canting of the antiferromagnetic coupling of the Fe-based and Ni-based sublattices via Dzyaloshinsky-Moriya interaction. Moreover, the substitution of Ni for Fe was effective for the enhancement of ferroelectric properties. The x=0.6 sample exhibits a maximum remnant polarization P_r of 37.8 μC/cm² because of a lower leakage current. The rather large activation energy in the x=0 and 0.2 samples implies that the relaxation process may be not associated with the thermal motion of oxygen vacancies inside the bulk.     

Modified multiferroic properties in narrow bandgap (1-x)BaTiO3-xBaNb1/3Cr2/3O3-δ ceramics

Perovskite oxides of formula (1-x)BaTiO₃-xBaNb_1/3Cr_2/3O_3-δ ((1-x)BT-xBNC), a series of lead-free ferroelectric photovoltaic compounds, have been sintered via the solid-state reaction technology and simultaneously show ferromagnetic orders and bandgap narrowing effects at room-temperature (RT). X-ray diffraction patterns reveal the doping-induced transition from tetragonal to cubic phase, which is explained by a possible mechanism. Raman spectroscopy analysis not only further confirms the presence of structural transition, but also indicates the difference in local crystal symmetry compared with the idealized cubic phase. Moreover, the minimum bandgap of as-prepared samples is about 2.1 eV, much smaller than that of the pure BT ceramic (3.1 eV), which is attributed to Cr³⁺ 3d orbits within the highest occupied orbital and the lowest unoccupied orbital of BT. It is noted that the higher doping concentration is conducive to the ferromagnetic order but unfavourable to the ferroelectric polarization. The above results exhibit the abundant physical phenomena and provide a method to design the solar-energy device and the multiferroic information storage application.     

Ultralow sintering temperature and piezoelectric properties of Bi(Zn1/2Ti1/2)O3−BiScO3−PbTiO3 for low-temperature co-firing applications

Bi(Zn_1/2Ti_1/2)O₃−BiScO₃−PbTiO₃ (BZT−BS−PT) high Curie temperature piezoelectric ceramics were synthesized by the conventional solid-state reaction method. Systematical investigations on the sintering, piezoelectric, and dielectric properties of the piezoceramics have been conducted. It was found that the sintering temperature could be remarkably depressed by varying the compositions in BZT−BS−PT systems. For composition of 11BZT−34BS−55PT ceramic, the sintering temperature is even lowered down to 750°C without any extra additions of sintering aids. Meanwhile, the ceramic sintered at this ultralow temperature presents dense microstructure with relative density up to 97%, as well as optimal properties of piezoelectric coefficient d₃₃ of 336 pC/N and Curie temperature of 415°C. The mechanism of low sintering temperature may be ascribed to the low melting point bismuth-based components in BZT−BS−PT solid solutions. Furthermore, 11BZT−34BS−55PT multilayer ceramics have been co-fired at 750°C with Ag internal electrodes. The dense structures, low cost, and optimal comprehensive properties of the co-fired multilayers illustrate obvious advantages of the ultralow sintering temperature in LTCC devices, implying promising applications of this Bi(Zn_1/2Ti_1/2)O₃−BiScO₃−PbTiO₃ high Curie temperature ternary system.     

Varistor and electrical properties of MgO.(Fe2O3)1−x(Bi2O3)x ceramics

In this study, MgO.(Fe₂O₃)_1−x(Bi₂O₃)_x (x = 0.01, 0.02, 0.04, 0.08) samples were prepared by the conventional ceramic process. Microstructure studies revealed that the samples contain MgFe₂O₄ grains surrounded by insulating Bi₂O₃-rich phases. DC electrical resistivity of the samples was increased by Bi₂O₃ content up to 1.1 MΩ.cm for the sample with x = 0.08. Current density- electric field investigations suggested that the samples with x = 0.01, 0.02 and 0.04 exhibited varistor properties. The sample with x = 0.01 showed excellent varistor properties with a non-linear coefficient of 45 and a threshold electric field value of 160 V/cm. Variation of D.C electrical conductivity versus temperature indicated that the activation energy values for the conduction were increased by Bi₂O₃ content from 0.334(5) eV to 0.857(5) eV. A.C electrical conductivity spectra of the samples obey the universal power law and the charge transport mechanism is based on electron hopping via sudden translational motion between the ferric and ferrous ions.     

Film formation in the Bi2O3 — TiO2 — Fe2O3 ternary system

The processes of film formation in a ternary system are studied, beginning with the preparation of the working solution and up to coat firing. It is demonstrated that the properties and quality of a coating are determined at the stage of preparing a film-forming solution and depend on the size and shape of the sol particles, the film porosity, and the diffusion process at the glass-film interface.     

Modified optical and magnetic properties at room-temperature across lead-free morphotropic phase boundary in (1-x)BiTi3/8Fe2/8Mg3/8O3–xCaTiO3

Perovskite compounds of the formula (1-x)BiTi_3/8Fe_2/8Mg_3/8O₃–xCaTiO₃ ((1-x)BMFT-xCTO), a class of highly potential ferroelectric photovoltaic materials with a morphotropic phase boundary (MPB), have been synthesized by solid-state reaction and exhibit simultaneously visible-light response and ferromagnetic order at room-temperature (RT). The effects of structural phases and lattice distortions on electron transitions and orbital orderings are systematically investigated. The crystal lattice displays constriction with increasing x and Raman peaks show non-liner shift due to Bi³⁺ and Fe³⁺/Mg²⁺ replaced by Ca²⁺ and Ti⁴⁺ randomly, respectively. Microstructural characterizations illustrate the rhombohedral-orthorhombic MPB occurrence during the crystal growth. Optical spectroscopy analysis shows band-gaps of our samples are about 2.2 eV with anomalies at the point of phase transition. Furthermore, the (1-x)BMFT-xCTO displays RT ferromagnetism when x<0.15, which can be explained by an F center theory. These results reveal rich physical phenomena and open an avenue to design promising perovskites for solar-energy conversion devices and multiferroic applications.     

Intramuscular injection of antigens and adjuvant preferentially decreases 18∶2n−6 and 18∶3n−3 in pig neck muscle

Linoleic (18∶2n−6) and α-linolenic acids (18∶3n−3) have many important physiological functions including immunomodulation. We tested how immunization influences the metabolism of 18∶2n−6 and 18∶3n−3 in the neck muscle of pigs. At 35 d old, pigs received either an intramuscular neck injection containing hen egg white lysozyme (HEWL), killed Mycobacterium tuberculosis, and Freund’s complete adjuvant (immunized) or PBS (control). At 49 d old, immunized pigs received a booster injection of HFWI and Freund’s incomplete adjuvant, and the control pigs received PBS into the neck. At 56 d old, all pigs received an intradermal injection of Mycobacterium bovis into the hind leg to induce a delayed-type hypersensitivity (DTH) reaction. At 57 d old, immunized pigs had a twofold increase in serum haptoglobin, a 10-fold increase in antibodies to HEWL, and the skinfold at the DTH reaction site was 10 times thicker than the controls. Both 18∶2n−6 and 18∶3n−3 (% composition) were approximately 25% lower in muscle IG, 40% lower in FFA, 50% lower in phospholipids, but not different in cholesteryl esters of the neck muscle of immunized pigs. The antigens in this model induce an increased response in the innate (haptoglobin), humoral (antibodies), and cellular (DTH) immune systems as well as a preferential decrease of 18∶2n−6 and 18∶3n−3 in the inflamed neck muscle. It appears that 18∶2n−6 and 18∶3n−3 are preferentially metabolized (possibly β-oxidized) in response to antigens.     

High-conducting Bi4V2−xFexO11-δ ceramics containing Fe2O3 nanocrystals: Structure and properties

The topography, structure, thermal, magnetic, and electrical properties of Bi₄V_2?xFe_xO_11-δ ceramics substituted with x = 0.5 and 0.7 Fe were studied. The microscope analysis showed the presence of iron-rich nanocrystals formed on the Bi-Fe-V-O grains. The X-ray diffraction studies confirmed that grains are built mostly of tetragonal Bi₄V_1.5Fe_0.5O_10.5 phase. Thermal properties analysis showed an order-disorder type γ ? γ? phase transition at a temperature of around 916 K, pronounced in samples doped with x = 0.5 Fe. The magnetic anomaly was observed in ceramics doped with x = 0.7 Fe which was assigned to Morin transition of Fe₂O₃. The conductivity was measured over a wide frequency range from 10 mHz to 1 MHz and at a wide temperature range from 373 to 923 K, using impedance spectroscopy. The D.C. conduction process was due to oxygen vacancies hopping while at low temperatures electron holes hopping is also possible.     

Bi2O2CO3/Fe3O4磁性复合物在环境污染治理领域中的应用

以Fe₃O₄纳米粒子和Bi₂O₂CO₃为原料,采用溶剂热法制备Bi₂O₂CO₃/Fe₃O₄磁性复合物,并通过对印染废水中染料的去除、剩余污泥厌氧消化过程中产甲烷潜力的影响两方面探讨其在环境污染治理中的应用。借助X射线衍射（XRD）、扫描电镜（SEM）、傅里叶红外光谱（FTIR）和比表面积及孔径分析对Bi₂O₂CO₃/Fe₃O₄复合物进行表征分析,SEM分析结果表明复合物表面较粗糙,BET结果显示复合物的比表面积为9.2294m²/g,Fe₃O₄的引入大幅度增加了Bi₂O₂CO₃的比表面积,使其具有明显的介孔结构。一方面,以甲基橙（MO）为目标污染物,研究了不同实验条件下该材料对染料的去除效果,结果表明,最大吸附量可达14.373mg/g,且该吸附反应过程符合拟二级动力学和Langmuir吸附等温模型,趋于单分子层吸附;另一方面,评估了复合物对污泥厌氧消化产甲烷潜力的影响,结果表明,复合物的引入对污泥厌氧消化产甲烷过程有一定的促进作用,累积产甲烷量相比于对照组提高了10%。分别用一级动力学模型和修正Gompertz模型模拟厌氧消化过程,模拟结果显示一级动力学模型可以更好地描述引入Bi₂O₂CO₃/Fe₃O₄磁性复合物的污泥厌氧消化过程。     

Relationship of structural phase transformations and properties of sol-gel films in the Bi2O3 — TiO2 — Fe2O3 system

It is shown that the structure and properties of gel-sol oxide films depend on the total mass content of film-forming oxides in the solution and are determined by the different degrees of nonequilibrium of the physicochemical processes. The existence of quite clear relationships between the solution viscosity, the specifics of the microstructure, and certain properties of the film is established. Translated from Steklo i Keramika, No. 4, pp. 11 – 14, April, 2000.     

Microwave dielectric properties of Bi2O3-doped Ca[(Li1/3Nb2/3)1−xTix]O3−δ ceramics

The effect of the additive on the densification, low temperature sintering, and microwave dielectric properties of the Ca[(Li_1/3Nb_2/3)_1−xTi_x]O_3−δ(CLNT) was investigated. Bi₂O₃ addition improved the densification and reduced the sintering temperature from 1150 to 900 °C of CLNT microwave dielectric ceramics. As the Bi₂O₃ content increased, the dielectric constant (ε_r) and bulk density increased. The quality factor (Q·f₀), however, was decreased slightly. The temperature coefficient of resonant frequency (τ_f) shifted to a positive value with increasing Bi₂O₃ content. The dielectric properties (ε_r, Q·f_0, τ_f) of Ca[(Li_1/3Nb_2/3)_0.95Ti_0.05]O_3−δ and Ca[(Li_1/3Nb_2/3)_0.8 Ti_0.2]O_3−δ with 5 wt.% Bi₂O₃ sintered at 900 °C for 3 were 20, 6500 GHz, −4 ppm/°C, and 35, 11,000 GHz, 13 ppm/°, respectively. The relationship between the microstructure and dielectric properties was studied by X-ray diffraction (XRD), and SEM.     

Na0.5Bi0.5TiO3 phase relations: Thermodynamics and phase equilibria in the systems Bi2O3 – TiO2, Na2O – TiO2, and Na2O – Bi2O3 – TiO2

The lead-free piezoelectric material sodium bismuth titanate (NBT, Na_0.5Bi_0.5TiO₃) has attracted considerable attention owing to its promising dielectric, piezoelectric, and electrical properties. However, the literature on the binary subsystems is contradictory and there are only limited data for the ternary system. The present work surveys all of the reports of the binary subsystems Bi₂O₃ – TiO₂ and Na₂O – TiO₂ and synthesizes these data into inclusive revised versions. The compatibilities for the ternary system Na₂O – Bi₂O₃ – TiO₂ were determined experimentally, thus enabling the construction of a complete isothermal section at 800 °C. The compatibilities associated with the problematic binary subsystem Na₂O – Bi₂O₃, which experiences extreme volatilisation, were determined through the generation of the absent standard-state thermodynamic functions for the relevant binary and ternary phases, thus providing a full suite of thermodynamic data for this system. The thermodynamic stability diagrams for Na₂O, Bi₂O₃, and TiO₂ thus were calculated. The isothermal section also addresses the contradictions in the literature concerning the formation of solid solutions of Bi₁₂TiO_20-x / Bi_12-xTi_1+xO_20+0.5x, pyrochlore (Bi₂Ti₂O₇ / Na_wBi_2-xTi_2-yO_7-z), BTO (Bi₄Ti₃O₁₂ / Na_xBi₄Ti₃O_12+0.5x), and NBT (Na_0.5Bi_0.5TiO₃ / Bi_1±xNa_xTiO_3.5±x). Further, it was observed that the congruent melting point of NBT, which was determined to be 1225 °C, was preceded by the onset of gradual structural destabilization at 940 °C. Also, the NBT rhombohedral → tetragonal phase transformation was observed at an onset temperature of ∼250 °C. The present work thus provides platform data for the fabrication and reactivities of materials in the ternary system Na₂O – Bi₂O₃· TiO₂ and its binary subsystems.     

The magnetization reversal and high temperature dielectric response in Y1−xHoxFe0.5Cr0.5O3

The structural, magnetic, and dielectric properties of the Y_1−xHo_xFe_0.5Cr_0.5O₃ (x=0, 0.05, 0.1, 0.3, and 0.5) compounds have been investigated. Rietveld refinement of the XRD patterns shows that the compounds possess orthorhombic perovskite structure. The dual magnetization reversal is observed in the samples with x=0.05 and 0.1, and it vanishes when x≥0.3. Ferromagnetic-like behavior with large coercive fields is observed in all Ho³⁺ doped YFe_0.5Cr_0.5O₃ samples, indicating a doping induced metamagnetic behavior. This abnormal magnetization behavior can be explained by the antiparallel magnetic coupling between the Ho³⁺ and the canted Cr³⁺/Fe³⁺ moments, as well as the Ho–O–Ho magnetic interaction. The dielectric behavior in the frequency range from 100 Hz to 10 MHz is investigated. The low doped samples (x=0, 0.05, and 0.1) exhibit relaxation-like dielectric behavior and colossal dielectric constant in a wide temperature and frequency range. The dual magnetization reversal under low magnetic field makes these materials attractive candidates for the magnetic dual sensor devices.     

Variation of crystal structure and defect luminescence in Ca3−xSrxAl2O6 phosphors

Ca_3−xSr_xAl₂O₆(x=0, 1.07, 1.88, 1.98, 3) phosphors were prepared through solid state reaction route under different atmospheres and two kinds of oxygen-defects were identified in Ca_3−xSr_xAl₂O₆ by means of X-ray photoelectron and electron spin-resonance spectra. Their defect luminescence behavior was discussed based on photoluminescence spectra as well as the calculation of bond volume polarizability of chemical bonds. Interstitials oxygen O_i is easily formed by the lattice oxygen (O1) with increasing Sr²⁺ content and air atmosphere may also provide O_i(O_i=1/2O₂). Besides, emission intensities of samples regularly changed by accommodating more O_i in air. By selecting proper excitation energy (276/355 nm), emission occurred from different O_i defect centers, with Spectral regions from 350 nm to 600 nm. Analysis suggested that the tunable emission characteristic at different excitation energies was linked with abnormal O_i, which was located in the interior of [AlO₄] six-member rings and the capacity of accommodating O_i is related to the size of six-member rings. Based on the theoretical and experimental results, a model was proposed to explain the mechanisms related to emission tunability accordingly. This research may help elucidate emission induced by an oxygen defects system.     

Dielectric behaviors of Nb2O5–Co2O3 doped BaTiO3–Bi(Mg1/2Ti1/2)O3 ceramics

Nb₂O₅ and Nb–Co doped 0.85BaTiO₃–0.15Bi(Mg_1/2Ti_1/2)O₃ (0.85BT–0.15BMT) ceramics were investigated. From XRD patterns, undesired phase was observed when the (Nb₂O₅/Nb-Co) doping levels exceed 3 wt.%/2 wt.%, giving rise to the deteriorate dielectric constant. The 0.85BT–0.15BMT ceramics doped with 2 wt.%Nb₂O₅ was found to possess a moderate dielectric constant (? ～ 1000) and low dielectric loss (tan δ = 0.9%) at room temperature and 1 kHz, showing flat dielectric behavior over the temperature range from ?55 to 155 °C. It was found that the formation of core–shell structure in the BT based ceramics is controlled by the doping sequence of Nb- and Bi-oxides.     

Energy storage and discharge performance for (1−x)BaSrTiO3−xBi(Zn1/2Ti1/2)O3 ceramics

Although lead-free dielectric ceramics have been widely studied to obtain excellent dielectric properties and good energy storage properties, the primary challenge of low energy storage density has not yet been resolved. Here, we introduce the concept of crossover relaxor ferroelectrics, which represent a state intermediate between normal ferroelectrics and relaxor ferroelectrics, as a solution to address the issue of low energy density. The (1−x)BaSrTiO₃−xBi(Zn_1/2Ti_1/2)O₃ (x = 0,.05, .1, .15, .2) ceramics were prepared by a solid-state method. Remarkably, 0.85BST–0.15BZT ceramics achieved a high recoverable energy density (W_rec) of 2.18 J/cm³ under an electric field of 240 kV/cm. BST–BZT materials exhibit substantial recoverable energy density, high breakdown strength, and superior energy efficiency, positioning them as a promising alternative to meet the diverse demands of high-power applications.     

Fabrication and characterization of La2O3–Fe2O3–Bi2O3 nanopowders: Effects of La2O3 addition on structure,optical, and radiation-absorption properties

In this study, we fabricated and characterized six new nanopowders representing variations of La₂O₃–Fe₂O₃–Bi₂O₃, i.e., 100Bi₂O₃, 30Fe₂O₃–70Bi₂O₃, 3La₂O₃–27Fe₂O₃–70Bi₂O₃, 7La₂O₃–23Fe₂O₃–70Bi₂O₃, 10La₂O₃–20Fe₂O₃–70Bi₂O₃, and 20La₂O₃–10Fe₂O₃–70Bi₂O₃ (represented by 100B, 30F70B, 3L27F70B, 10L20F70B, and 20L10F70B, respectively). These nanopowders were prepared by the microwave-assisted hydrothermal synthesis method. Saponin extract from soapnuts was used as the nanoparticle capping agent. The structural, optical, and gamma radiation characteristics were measured, calculated, and analysed, respectively. The chemical structures of the nanocomposites influenced their optical and radiation shielding characteristics. The optical bandgaps of the 100B, 30F70B, 3L27F70B, 7L23F70B, 10L20F70B, and 20L10F70B nanopowders were 3.16, 3.13, 3.43, 3.45, 3.46, and 3.58 eV, respectively. The ranges of the mass attenuation coefficients of the nanopowders were computed, using XCOM, to be 0.0412–5.1624, 0.0401–4.5406, 0.0401–4.5285, 0.0401–4.5129, 0.0401–0.5015, and 0.0400–4.4156 cm²/g, respectively, and the ranges of mass energy absorption coefficients were found to be 0.0232–1.7525, 0.0228–1.5484, 0.0228–1.5598, 0.0288–1.5746, 0.0228–1.5853, and 0.0227–1.6192 cm²/g, respectively, for photon energies in the range of 0.1–10 MeV. The order of the dose rate trend was as follows: 30F70B < L27F70B < 7L23F70B < 10L20F70B < 20L10F70B. Analysis of the photon interaction parameters showed that the synthesized nanopowders could function well as fillers in radiation-shielding matrices.     

Enhancing high power performances of Pb(Mn1/3Nb2/3)O3–Pb(Zr,Ti)O3 ceramics by Bi(Ni1/2Ti1/2)O3 modification

High power piezoelectric ceramics 0.04Bi(Ni_1/2Ti_1/2)O₃-xPb(Mn_1/3Nb_2/3)O₃-(0.96-x)Pb(Zr_yTi_1-y)O₃ (BNT-xPMnN-PZ_yT) with various contents of PMnN from 0 to 12 mol% (keep y = 0.50) and Zr/Ti ratio gradually increasing from 48/52 to 52/48 (keep x = 0.06) were prepared by solid-state method. X-ray diffraction (XRD) results show a single phase of polycrystalline perovskite and indicate that the phase structure transforms from tetragonal phase to rhombohedral with x and y increasing. The optimal comprehensive properties of BNT-xPMnN-PZ_yT ceramic, d₃₃ (355 pC/N), k_p (0.58), ε_r (1512), tanδ (0.40%), T_c (336 °C) and Q_m (2010), are obtained at x = 0.06 and y = 0.50, which are apparently superior to typical or commercial Pb(Zr,Ti)O₃ (PZT) based power ceramics. Within the range from room temperature to 200 °C, the variation of electric-field induced strains is less than 8.3%, indicating its good temperature stability. The maximum vibration velocity of the ceramic at temperature rise of 20 °C is measured to be 0.92 m/s, which is about 2 times higher than that of commercial hard PZT ceramics, suggesting the BNT-xPMnN-PZ_yT ceramic is a competitive and potential candidate for power piezoelectric transduction and actuation applications.     

Tunable magnetic coupling and dipole polarization of core-shell Magnéli Ti4O7 ceramic/magnetic metal possessing broadband microwave absorption properties

There are few reports on the application of Magnéli Ti₄O₇ in the field of electromagnetic wave absorption. Herein, we designed and prepared a Ti₄O₇/magnetic metal composite via an electrostatic assembly with in-situ reduction reaction. This system utilized distinct magnetic coupling deriving from the subtle designed structures and magnetic-dielectric synergy. The core-shell magnetic metallic nanoparticles/oxygen deficient Ti₄O₇ are useful microwave absorbers in terms of wide broadband, strong absorption and ultra-low filler amount. The optimal reflection loss of Ti₄O₇@CoNi composite was −43.6 dB at 2.5 mm, meanwhile the effective absorbing band could reach over 5.12 GHz at only a 2.7 mm thickness. The results confirm that the dependence of the electromagnetic characteristics of the absorber on the filler ratio, frequency, and absorber thickness. Therefore, this work may be beneficial in constructing core-shell structured magnetic metal/Magnéli Ti₄O₇ composites to tune electromagnetic parameters and strengthen electromagnetic absorption.     

Electro-catalytic characterization and dye degradation of Ti1−x(Bi)xO2 in acidic solution

The authors in this study used the sol–gel process to prepare Bi-doped TiO₂ as a novel electrocatalyst. Results show that Bi can be doped successfully into TiO₂ from 1% to 90%. The electrical conductivity of a 1% Bi-doped TiO₂ particle-suspended solution is increased nearly twice that of pure TiO₂. The electro-catalyzing property of the synthesized Bi-doped TiO₂ catalyst was performed under acidic conditions toward a methyl blue dye solution. The observed removal percentage of methyl blue dye was from 5% to 75%. The optimized electro-catalyzing condition was observed at 5% Bi-doped TiO₂ with a working voltage of 5 V.