Saturated Hysteresis Loops Research Articles

Effect of excess of bismuth doping on dielectric and ferroelectric properties of BaBi4Ti4O15 ceramics

The effect of excess bismuth oxide Bi2O3 (2–10wt%) for processing BaBi4Ti4O15 (BBT) ceramics by solid state reaction has been investigated. The formation of a single phase and a change in the orthorhombic distortion are confirmed with varying excess of bismuth content. Changes in the density are marginal, and use of excess bismuth is seen to promote enhanced grain growth. Dielectric response is improved markedly exhibiting reduced dielectric losses and dispersion over a wide frequency range (10−3–106Hz). A high dielectric constant (ε′~226), low loss factor (tanδ~0.01) and low dc conductivity (σdc~10–14Ω−1cm−1) are achieved with an optimum content 6–8wt% of excess of bismuth oxide. Temperature dependent dielectric data fits well to the modified Curie–Weiss law and the frequency dependent maximum temperatures (Tm and Tm1) corresponding to real and imaginary parts of dielectric permittivity (ε′ and ε″) show a good fit to the non-linear Vogel–Fulcher (V–F) relationship. A clear relaxor behavior is observed with a degree of diffuseness, γ~1.97. Saturated hysteresis loops with high remnant polarization (Pr~12.5μC/cm2), low coercive fields (Ec~26kV/cm) are measured and a high piezoelectric coefficient (d33~29pC/N) is achieved in poled BaBi4Ti4O15 ceramics prepared with up to 8wt% of excess bismuth oxide. Such a relaxor ferroelectric material with high Curie temperature is useful for high temperature piezoelectric transducer applications.

Saturated hysteresis loops and conduction mechanisms in Mn-doped BiFeO3 thin films derived from sol–gel process

Mn-doped BiFeO3 (BFO) thin films with nominal composition of BiFe1−x Mn x O3 (x = 0.00, 0.01, 0.03, 0.05, 0.07) were deposited on (111)Pt/Ti/SiO2/Si substrates via a simple sol–gel spin-coating method with rapid thermal annealing process. The BFO films with different Mn dopant contents were well crystallized in the perovskite structure and their overlapped (110) diffraction peaks shifted toward higher angles with the increase in Mn content, indicating a slight distortion in the lattice structure. Improved microstructure with smaller grain size and diminished structural defects can be observed in the films of x around 0.03. X-ray photoelectron spectroscopy analysis confirmed the coexistence of 2+ and 3+ electronic states for Fe element and proper substitution of Mn for Fe can decrease the amount of Fe2+ while excess doping results in increasing Fe2+ content. The intrinsic ferroelectric polarization was hard to be measured in the pure BFO film due to high leakage contribution, whereas the x = 0.03, 0.05 and 0.07 films exhibited well-saturated rectangular shape-like ferroelectric hysteresis loops, and more importantly, perfectly closed hysteresis loops were obtained for the x = 0.03 film with a 2Pr value of 85.2 µC/cm2. The leakage current density in high electric field region was dramatically decreased by Mn doping, e.g. decreased to 3.3 × 10−4 A/cm2 at electric filed intensity of 170 kV/cm for the x = 0.03 film. Detailed leakage current characteristic analysis suggested that the dominant conduction mechanism in the pure BFO film was the space charge limited conduction at medium/high electric fields, which was associated with the space charges originated by oxygen vacancies; however, the leakage current of the x = 0.03 film was dominated by the Schottky mechanism in medium/high electric field region.

Electrical Characterization and Microstructures of Bi<sub>4-x</sub>Dy<sub>x</sub>Ti<sub>3</sub>O<sub>12</sub> Ceramics

The electrical properties of Dy-doped bismuth titanate,Bi4-xDyxTi3O12(BDT) ceramics prepared by a conventional electroceramic technique were investigated. XRD analyses revealed Bi-layered perovskite structure in all samples. SEM micrographs showed randomly oriented and plate-like morphology. For the samples with x=0.25 and 1.0 the current-voltage characteristics exhibited negative differential resistance behaviors and their P-V hysteresis loops were characterized by large leakage current, whereas for the samples with x=0.5 and 0.75 the current-voltage characteristics showed simple ohmic behaviors and their P-E hysteresis loops were the saturated and undistorted hysteresis loops. The remanent polarization ( Pr) and coercive field (Ec) of the BDT ceramic with x=0.75 were above 16μC/cm2and 75KV/cm , respectively.

Effect of Gd Substitution on Electrical Characteristics and Microstructures of Bi<sub>4</sub>Ti<sub>3</sub>O<sub>12</sub> Ceramics

The electrical properties of Gd-doped bismuth titanate Bi4-xGdxTi3O12 (BGT) ceramics prepared by a conventional electroceramic technique were investigated. XRD analyses revealed Bi-layered perovskite structure in all samples. SEM micrographs showed randomly oriented and plate-like morphology. For the ceramics with x=0.25 and 1.0 the current-voltage characteristics exhibited negative differential resistance behaviors and their P-E hysteresis loops were characterized by large leakage current, whereas for the ceramics with x=0.5 and 0.75 the current-voltage characteristics showed simple ohmic behaviors and their P-E hysteresis loops were the saturated and undistorted hysteresis loops. The remanent polarization ( Pr ) and coercive field (Ec) of the BGT ceramic with x=0.8 were above 16μC/cm2 and 70KV/cm , respectively.

Ferroelectric Characteristics of Bi<sub>4-x</sub>Pr<sub>x</sub>Ti<sub>3</sub>O<sub>12</sub> Ceramics

The electrical properties of Pr2O3-doped bismuth titanate,Bi4-xPrxTi3O12 (BPT) ceramics prepared by a conventional electroceramic technique were investigated. XRD analyses revealed Bi-layered perovskite structure in all ceramics. SEM micrographs showed randomly oriented and plate-like morphology. For the ceramics with x=0.25 and 1.0 P-E hysteresis loops were characterized by large leakage current, whereas for the ceramics with x=0.5 and 0.75 P-E hysteresis loops were the saturated and undistorted hysteresis loops. The remanent polarization ( Pr ) and coercive field (Ec) of the BPT ceramic with x=0.75 were above 18μC/cm2 and 65KV/cm , respectively.

Electrical Characteristics and Microstructures of Pr<sub>2</sub>O<sub>3</sub>-Doped Bi<sub>4</sub>Ti<sub>3</sub>O<sub>12</sub> Thin Films

Pr2O3-doped bismuth titanate (Bi4-xPrxTi3O12: BPT) thin films with random oriention were fabricated on Pt/Ti/SiO2/Si substrates by rf magnetron sputtering technique, and the structures and ferroelectric properties of the films were investigated. XRD studies indicated that all of BPT films consisted of single phase of a bismuth-layered structure with well-developed rod-like grains. For samples with x=0..0 , 0.25, 1.0 and 1.25, I-E characteristics exhibited negative differential resistance behaviors and their ferroelectric hysteresis loops were characterized by large leakage current, whereas for samples with x=0.5 and 0.75, I-E characteristics were simple ohmic behaviors and their ferroelectric hysteresis loops were the saturated and undistorted hysteresis loops. The remanent polarization ( Pr ) and coercive field (Ec) of the BPT Film with x=0.75 were above 30μC/cm2 and 75KV/cm , respectively.

Doping Strategies of Bi (Ti<sub>0.5</sub>Ni<sub>0.5</sub>)O<sub>3</sub> for Increased Performance in BiFeO<sub>3</sub>

Investigation of crystal structure, dielectric, magnetic and local ferroelectric properties of the diamagnetically substituted (1-x)BiFeO3-xBi (Ti0.5Ni0.5)O3 solid solutions samples have been carried out. The solid solutions have been found to possess a rhombohedrally distorted perovskite structure described by the space group R3c. Compared with pure BiFeO3 compound, both ferroelectric and magnetic properties are much improved by solid solution with Bi (Ti0.5Ni0.5)O3 with saturation hysteresis loops observed. Among all the samples, the x=0.1 samples shows the optimal ferromagnetism with Mr~0.56531emμ/g and the optimal ferroelectricity with Pr~5.767μC/cm2 at room temperature.

Electrical and Magnetic Properties of Multiferroic BiFeO<sub>3</sub> Ceramics Prepared Using Sol-Gel Derived Fine Powders

Insulating BiFeO3ceramics with a small amount of secondary phase Bi2Fe4O9were prepared by rapid sintering at 840 °C using sol-gel derived fine powders. The ceramics are dense and consist of grains of 3∼8μm in size. Their leakage current density remains lower than 5.5×10−5A/cm2under the applied electrical field below 100 kV/cm. The main conduction mechanism from 50−190 kV/cm is space-charge-limited-current relating to oxygen vacancies. The ceramics exhibit a saturated ferroelectric hysteresis loop with a remanent polarization (2Pr= 22μC/cm2) under the applied field of 165 kV/cm. Weak ferromagnetism was observed with a remanent magnetization 2Mrof 1.2×10−4μB/Fe at 300 K and of 1.8×10−4μB/Fe at 10 K.

Enhanced magnetism in Cr-doped ZnO nanoparticles with nitrogen co-doping synthesized using sol–gel technique

Pure ZnO and 2 % Cr-doped ZnO nanoparticles were synthesized by sol–gel technique. Powder X-ray diffraction reveals that Cr incorporates into the ZnO crystal lattice without disturbing the original hexagonal structure. Transmission electron microscopy measurements show that the average size of these nanoparticles is in the range 20–25 nm. Pure ZnO nanoparticles exhibit diamagnetism while Cr-doped ZnO exhibit saturated hysteresis loop at room temperature indicating ferromagnetic behavior. Nitrogen co-doping along with Cr in ZnO shows enhanced ferromagnetism with small antiferromagnetism.

Anion Driven [CuIIL2]n Frameworks: Crystal Structures, Guest-Encapsulation, Dielectric, and Possible Ferroelectric Properties

Employing a flexible phosphoramide ligand L, PhPO(NH3Py)2 (3Py = 3-pyridyl), four new Cu(II) cationic coordination assemblies 1, 1a, 2, and 3 of composition {[Cu2L4(H2O)2]·(ClO4)4·(H2O)5·(CH3OH)}∞, {[Cu3L6(H2O)3]·(ClO4)5·(NO3)·(H2O)11}∞, {[Cu4L8(H2O)5]·(NO3)8·L·(H2O)9}, and {[Cu3L6]·(NO3)6·(H2O)8·(CH3OH)2}, respectively, were synthesized. The compounds 1 and 1a having perchlorate and mixed perchlorate-nitrate anions, respectively, were obtained as noncentrosymmetric 1D-helical assemblies. However, 2 and 3 were obtained as discrete centrosymmetric assemblies of composition M4L8 and M3L6, respectively. Interestingly, 2 can encapsulate the hydrated potassium cation [K(H2O)8]+ in its intrinsic cavity. The ferroelectric measurements of 1 and 1a gave a well saturated ferroelectric hysteresis loop giving saturation polarization (Ps) values of 1.8 and 0.55 μC/cm2, respectively. This indicates that the presence of nitrate anion in the packing structure has an effect in altering the asymmetry of the system, which c...

Ferroelectric and Piezoelectric properties of (111) oriented lanthanum modified lead zirconate titanate film

Lanthanum modified lead zirconate titanate (PLZT) thick film with molecular formula of Pb0.92La0.08(Zr0.52Ti0.48)0.98O3 was grown preferentially along (111) direction on Pt/SiO2/Si (platinum/silicon oxide/silicon) substrate by spin coating of chemical solution. The directional growth of the film was facilitated by platinum (Pt) (111) template and rapid thermal annealing. X-ray diffraction pattern and atomic force microscopy revealed the preferential growth of the PLZT film. The film was characterized for ferroelectric and detailed piezoelectric properties in a parallel plate capacitor (metal–PLZT–metal) configuration. Ferroelectric characterization of the film showed saturated hysteresis loop with remanent polarization and coercive electric field values of 10.14μC/cm2 and 42kV/cm, respectively, at an applied field of 300kV/cm. Longitudinal piezoelectric coefficient (d33,f) was measured by employing converse piezoelectric effect where electrical charge response and displacement were measured with electrical voltage excitation on the sample electrodes. The effective transverse piezoelectric coefficient (e31,f) was derived from charge measurement with an applied mechanical excitation strain by using the four point bending method. d33,f and e31,f coefficients of PLZT films were found to be 380pm/V and −0.831C/m2 respectively.

Temperature Dependence of Electric‐induced Light Scattering Performance for PLZT Ceramics

PLZT (7.45/71/29) ceramics with fully dense microstructure and high transmittance were fabricated by a hot‐press sintering method. The effects of temperature on the phase structure, ferroelectric property, and electric‐induced light scattering performance of the PLZT ceramics were examined and analyzed. XRD patterns indicated that the PLZT sample tended to transform from rhombohedral phase to tetragonal phase with the temperature increasing. And the temperature‐dependent ferroelectric hysteresis behavior of the PLZT sample revealed the conversion of a saturated square hysteresis loop to a double‐loop‐like hysteresis loop, accompanied with the significant reduction in coercive field and remnant polarization. Depending on the temperature, the PLZT sample exhibited three different kinds of electric‐induced light scattering performance.

Improved ferroelectricity of (1−x)Na0.5Bi0.5TiO3–xBaTiO3 ceramics rapidly sintered at low temperature

High insulating (1−x)Na0.5Bi0.5TiO3–xBaTiO3 (x=0–0.08) ceramics were rapidly sintered at low temperature and then enhanced polarizations were observed. (1−x)Na0.5Bi0.5TiO3–xBaTiO3 nano-powders were prepared by the sol–gel method and then their ceramics were rapidly sintered at 920–1150°C. According to the saturated ferroelectric hysteresis loops, the acquired saturated and remnant polarizations are ~48μC/cm2 and ~40μC/cm2 at x=0.03–0.08, and the coercive electric field decreases from ~70kV/cm of pure Na0.5Bi0.5TiO3 to ~30kV/cm at x=0.06–0.08. Furthermore, the piezoelectric d33 is 166.8pC/N at x=0.06, where the morphotropic phase boundaries occur. These improved properties are achieved because the leakage current is reduced through compressing the loss of Na and Bi components during ceramics׳ preparation process.

Potential of Magnetic Nanofiber Scaffolds with Mechanical and Biological Properties Applicable for Bone Regeneration

Magnetic nanofibrous scaffolds of poly(caprolactone) (PCL) incorporating magnetic nanoparticles (MNP) were produced, and their effects on physico-chemical, mechanical and biological properties were extensively addressed to find efficacy for bone regeneration purpose. MNPs 12 nm in diameter were citrated and evenly distributed in PCL solutions up to 20% and then were electrospun into nonwoven nanofibrous webs. Incorporation of MNPs greatly improved the hydrophilicity of the nanofibers. Tensile mechanical properties of the nanofibers (tensile strength, yield strength, elastic modulus and elongation) were significantly enhanced with the addition of MNPs up to 15%. In particular, the tensile strength increase was as high as ∼25 MPa at 15% MNPs vs. ∼10 MPa in pure PCL. PCL-MNP nanofibers exhibited magnetic behaviors, with a high saturation point and hysteresis loop area, which increased gradually with MNP content. The incorporation of MNPs substantially increased the degradation of the nanofibers, with a weight loss of ∼20% in pure PCL, ∼45% in 10% MNPs and ∼60% in 20% MNPs. Apatite forming ability of the nanofibers tested in vitro in simulated body fluid confirmed the substantial improvement gained by the addition of MNPs. Osteoblastic cells favored the MNPs-incorporated nanofibers with significantly improved initial cell adhesion and subsequent penetration through the nanofibers, compared to pure PCL. Alkaline phosphatase activity and expression of genes associated with bone (collagen I, osteopontin and bone sialoprotein) were significantly up-regulated in cells cultured on PCL-MNP nanofibers than those on pure PCL. PCL-MNP nanofibers subcutaneously implanted in rats exhibited minimal adverse tissue reactions, while inducing substantial neoblood vessel formation, which however, greatly limited in pure PCL. In vivo study in radial segmental defects also signified the bone regeneration ability of the PCL-MNP nanofibrous scaffolds. The magnetic, bone-bioactive, mechanical, cellular and tissue attributes of MNP-incorporated PCL nanofibers make them promising candidate scaffolds for bone regeneration.

Characterizations of diverse mole of pure and Ni-doped α-Fe2O3 synthesized nanoparticles through chemical precipitation route

In the present study, an attempt has been made for characterization and synthesis of pure and Ni-doped α-Fe2O3 (hematite) nanoparticles by chemical precipitation method. The synthesized products have been studied by X-ray diffraction (X-RD), Fourier transform infrared (FTIR) spectroscopy, UV–Vis diffuse reflectance spectroscopy (UV–Vis DRS), vibrating sample magnetometer (VSM) and scanning electron microscopy (SEM) techniques. The estimated average diameter of α-Fe2O3 nanoparticles were calculated by using the Debye–Scherrer equation and established as 31nm. SEM micrographs showed the surface morphology as well as structures and particles distributions of synthesized samples. The UV–Vis DRS showed the indirect and direct band gap energies of pure and Ni-doped α-Fe2O3, these were reduced from 1.9847 to 1.52eV and 2.0503 to 1.76eV respectively. This result suggested the dopant enhanced the semiconducting behavior of iron oxide nanoparticles to an extent proportional to its nickel doped in the α-Fe2O3. Further, the magnetic properties of the pure and doped samples were investigated by vibrating sample magnetometer (VSM) and evaluated the information of pure and doped samples exhibited saturated hysteresis loop at room temperature, which is indicating that the weak ferromagnetism in nature of our synthesized samples. In addition, it has been found from the magnetization hysteresis curves of Ni-doping, resulting from increased the saturation of magnetization and reduced the coercivity of used samples. Therefore, the present study showed the reduction in band gap energies and coercive field for α-Fe2O3 nanoparticles due to nickel doped.

Structural and phase sensitivity of the coercive force of a minor hysteresis loop of steel

Coercive force H c of a minor hysteresis loop of steel is shown to be determined by the parameters of the saturation hysteresis loop. The sensitivity of H c to the structure- and phase-sensitive parameters of a metal is analyzed, a technique for an effective use of the results of measuring H c in magnetic structural analysis is developed, and the problems of controlling metal manufacture conditions to be solved by measuring H c are formulated.

Hierarchically Ordered Nano‐Heterostructured PZT Thin Films with Enhanced Ferroelectric Properties

Realization of ferroelectric (FE) devices based on the polarization effects of Pb(Zr0.52Ti0.48)O3 (PZT) has reinforced the investigation of this material in multiple dimensions and length scales. Multi‐level hierarchical nanostructure engineering in PZT thin films offer dual advantages of variable length‐scale and dimensionality. Here, the growth of hierarchically ordered PZT nano‐hetero­structures (Nhs) from PZT seed‐layer deposited on SrTiO3:Nb (100) substrates, using a physical/chemical combined methodology involving pulsed laser deposition (PLD) and hydrothermal processes, is reported. Systematic SEM, TEM, and Raman spectroscopy studies reveal mixed hetero‐ and homo‐epitaxial growth mechanism. In the final stage, 3D Nh units cross‐link and form a dense network‐like Nh PZT thin‐film. FE polarizations are measured without using any polymer fill‐layer which otherwise introduces huge dielectric losses and lowers the polarization values for a FE device. In benefit, well saturated and symmetric FE hysteresis loops are observed with high degree of squareness and a high remnant polarization (54 μC cm‐2 at a coercive field of 237 kV cm‐1). This work provides a pathway towards preparing hierarchical PZT Nhs offering coherent design of high‐performance FE capacitors for data storage technologies in future.

Study on ferroelectric behaviors and ferroelectric nanodomains of YMnO3 thin film

Hexagonal YMnO3 is a special kind of multiferroics which shows unique advantages in magneto-electric field due to its low permittivity and only c-axis polarization. However, its ferroelectric properties, especially domain structures, have not been intensively investigated. In this study, YMnO3 film about 270 nm in thickness is prepared on Si(100) substrate by sol-gel spin coating. Structure and morphology of the film are characterized by grazing incidence X-ray diffraction and atomic force microscopy. Domain structure and its reversal behavior on a nanoscale are examined by piezoresponse force microscopy (PFM). The leakage current and ferroelectric property are also investigated. The results show that the film displays a hexagonal perovskite structure with good crystallinity and has smooth surface with a root-mean-square roughness of 7.209 nm. PFM images and typical local piezoresponse loops reveal the good piezoelectric and ferroelectric properties of the YMnO3 film at room temperature. Meanwhile, the offsets of amplitude loop and phase loop are observed due to the internal electric field. Leakage current density of YMnO3 film is lower than 10-6 A·cm-2, so saturated hysteresis loop can be obtained.

Analysis of Cyclic Plastic Response of Heat Resistant Sanicro 25 Steel at Ambient and Elevated Temperatures

Austenitic heat resistant steel Sanicro 25 developed for high temperature applications in power generation industry has been subjected to selected low cycle fatigue tests at ambient and at elevated temperature. Saturated hysteresis loops at both temperatures were analyzed to deduce the probability density distribution of the internal critical stresses and to estimate the contribution of the effective stress for different strain amplitudes. The internal structure of the material at room and elevated temperature was studied using transmission electron microscopy and the results were discussed in relation to the cyclic stress- strain response

Ferroelectricity and magnetism in Pb(Fe0.5Nb0.5)O3–Pb(Yb0.5Nb0.5)O3–PbTiO3 single crystals

Domain structure, ferroelectric and magnetic properties of [001]-oriented multiferroic single crystals Pb ( Fe 0.5 Nb 0.5) O 3– Pb ( Yb 0.5 Nb 0.5) O 3– PbTiO 3 (PFN–PYN–PT) with various compositions were investigated with the purpose of understanding the ferroelectric and magnetic order. The samples were determined to be rhombohedral phase or coexistence of tetragonal and rhombohedral phases by means of X-ray diffraction analysis and optical study. Furthermore, the domain configuration in tetragonal phase always takes on 90° domain wall. All samples exhibit well-developed saturated hysteresis loop, indicating no substantial increase of conductivity despite the introduction of Fe 3+ ions. But the piezoelectric coefficients were reduced due to the introduction of PFN. In addition, the PFN–PYN–PT single crystals showed paramagnetic behavior, resulting from the – O – Fe 3+– O – Nb / Yb / Ti – O – Fe 3+– O – magnetic interaction. Interestingly, M–H hysteresis loops display a magnetic relaxor behavior.