Toward the Origin of Magnetic Field-Dependent Storage Properties: A Case Study on the Supercapacitive Performance of FeCo2O4 Nanofibers.

Despite the many reports in the literature on the magnetic field-dependent energy storage properties of metal oxides, the origin of magnetic field-dependent supercapacitive properties is still not clear. This is because electrode's properties such as physical (electrical and magnetic properties), structural and microstructural (surface area, pore size, and their distribution), and electrolyte's properties (ionic diffusion, ionic conductivity, cation size, etc.) are very crucial for investigating the effect of a magnetic field on the energy storage properties of metal oxides. In this article, the effect of a magnetic field on some of the abovementioned properties and thereby on the supercapacitive properties of FeCo2O4 (FCO) nanofibers is thoroughly investigated. The local magnetic environment of the magnetized electrode (magnetic gradient force, susceptibility, etc.) is proposed to be crucial for tuning the storage properties of the electrode material. Magnetic field-mediated resistive properties of the electrode material and thereby the induced magnetic gradient force at the electrode surface seem to be helpful in lowering the Nernst layer thickness and improving the electrode/electrolyte interface for a smoother ionic exchange resulting in 56% increment in the capacitance values of FCO nanofibers. A series of electrochemical experiments (cyclic voltammetry and galvanostatic charge-discharge) and magnetic property evaluation of bare and cycled electrodes are carried out, and the proposed mechanism/hypothesis is validated by studying the ex situ magnetic properties and the results are discussed in detail.

MWCNT/TiO2 hybrid nano filler toward high-performance epoxy composite.

In this work, multi-walled carbon nanotubes (MWCNTs) are decorated by TiO2 nanoparticles and formed a new hybrid structure of filler (MWCNT/TiO2 hybrid filler). The MWCNT/TiO2 hybrid filler is reinforced in epoxy matrix and studied the mechanical and anti-corrosion properties of epoxy. The morphology of newly formed MWCNT/TiO2 hybrid nano filler has been studied using transmission electron microscopy (TEM). Field Emission Scanning Electron Microscope (FESEM) images of tensile fracture surface confirmed the superior dispersion of MWCNT/TiO2 in the epoxy matrix. The resultant MWCNT/TiO2 hybrid-epoxy nanocomposite exhibits superior anti-corrosion and mechanical performance than the nanocomposite produced by loading of only MWCNTs or TiO2 nanoparticles as well as neat epoxy. For example, tensile strength and storage modulus of epoxy increased by 61% and 43% respectively on loading of MWCNT/TiO2 hybrid nano filler. Furthermore, the coating of MWCNT/TiO2 hybrid-epoxy nanocomposite on mild steel reduces the corrosion rate upto 0.87×10-3MPY from 16.81MPY.

Dielectric, magnetic and magnetoelectric properties of La and Nb codoped bismuth ferrite.

Single-phase Bi(0.80)La(0.20)FeO(3) (BLFO) and Bi(0.80)La(0.20)Fe(1-x)Nb(x)O(3) (BLFNO) samples were prepared in order to study the dielectric, magnetic and magnetoelectric properties of La and Nb codoped BiFeO3. Rietveld refinement of x-ray diffraction patterns of La and Nb codoped samples has been performed using the R3c space group. Magnetic hysteresis loops revealed that codoping can effectively increase the spontaneous magnetization due to change in the bond angle of Fe-O-Fe as a result of distortion created by the Nb5+ doping. Magnetic field-induced relative change of the dielectric constant for BLFO and BLFNO samples is a signature of magnetoelectric coupling.

Aliovalent-ion and magnetic field induced phase transition in multiferroic biFe(1-x)Ti(x)O3 system.

Multiferroic compounds with general formula BiFe(1-x)Ti(x)O3 (x = 0.1, 0.2, 0.3 and 0.35) have been synthesized by conventional solid state reaction method. The effect of Ti substitution on ferroelectric and magnetic properties is studied. From X-ray diffraction (XRD) analysis, a rhombohedral to orthorhombic phase transition for x > 0.3 was observed. From SQUID measurements, a magnetic field induced phase transition has been observed in the BiFe(1-x)T(x)O3 system for x = 0.3. An anomaly in dielectric constant and dielectric loss in the vicinity of antiferromagnetic Néel temperature (T(N)) and a small enhancement in magnetization have been observed. Magnetization measurements above room temperature showed no systematic variation in antiferromagnetic Néel temperatures on Ti substitution. Further it is seen that this system shows the coupling between electric and magnetic dipoles exhibiting magnetoelectric (ME) effect at room temperature and possess high dielectric constant.

Pr doped bismuth ferrite ceramics with enhanced multiferroic properties.

Pr modified Bi(0.9-x)La(0.1)Pr(x)FeO(3) (BLPFO-x, x = 0, 0.1 and 0.2) ceramics were prepared by the conventional method based on the solid state reaction of mixed oxides and a detailed study of electrical and magnetic properties of Pr modified bismuth ferrite (BLPFO) is reported. X-ray analysis shows the formation of a bismuth ferrite rhombohedral phase. Pr doping significantly increases the resistivity and leads to a successful observation of electrical polarization hysteresis loops. All the samples have been found to possess a spontaneous magnetic moment at room temperature which increases further at low temperatures. The strong dependence of remnant polarization and dielectric constant on the strength of magnetic field is a direct evidence of magnetoelectric coupling in BLPFO-2 ceramics.

Observation of the room temperature magnetoelectric effect in Dy doped BiFeO(3).

Polycrystalline Bi(1-x)Dy(x)FeO(3) (x = 0.0, 0.03, 0.05, 0.07 and 0.1) ceramics have been prepared via a mixed oxide route. The effect of Dy substitution on the dielectric, ferroelectric, and magnetic properties of the BiFeO(3) multiferroic perovskite is studied. Experimental results suggest that in the Bi(1-x)Dy(x)FeO(3) system, increase of the Dy concentration leads to effective suppression of the spiral spin structure of BiFeO(3), resulting in the appearance of net magnetization. An anomaly in the dielectric constant (ε) was observed in the vicinity of the antiferromagnetic transition temperature. All compositions show saturated polarization-field (P-E) curves. As a result, improved multiferroic properties of Bi(0.9)Dy(0.1)FeO(3) ceramics with remnant polarization and magnetization (2P(r) and 2M(r)) of 7.98 µC cm(-2) and 0.024 emu g(-1), respectively, were established. An enhancement in remnant polarization after poling the samples in the magnetic field was evidence of magnetoelectric coupling at room temperature.

Study of dielectric, magnetic, ferroelectric and magnetoelectric properties in the PbMn(x)Ti(1-x)O(3) system at room temperature.

We report magnetoelectric coupling at room temperature between ferroelectric and magnetic order parameters in Mn-doped PbTiO(3) compounds prepared by a solid-state reaction method. X-ray diffraction showed that PbMn(x)Ti(1-x)O(3) (x = 0.1, 0.3 and 0.5) compounds were single phase. The Mn substitution reduced the lattice distortion, i.e., the c/a ratio, and hence the ferroelectric Curie temperature (T(C)) decreased with increasing Mn content. High-temperature magnetization measurements showed that the ferromagnetic Curie temperature (T(M)) decreases with increasing Mn in PbMn(x)Ti(1-x)O(3). An anomaly in the dielectric constant (ε) was observed in the vicinity of the ferromagnetic transition temperature. These samples exhibited magnetism and ferroelectricity simultaneously at room temperature, which was evidenced from the coexistence of saturated magnetization and polarization hysteresis loops. An enhancement in saturation polarization after poling the samples in the magnetic field was evidence of magnetoelectric coupling at room temperature. An enhancement of 11-13% in polarization was observed after poling the samples in a magnetic field at 1.2 T.

Formation of hydroxyapatite in water, Hank's solution, and serum at physiological temperature.

The influence of de-ionized water, Hank's saline solution, and bovine calf serum on formation of stoichiometric (Ca/P = 1.67) hydroxyapatite (SHAp) at physiological temperature was studied. SHAp formed in aqueous solution by acid-base reaction of particulate Ca(H(2)PO(4))(2).H(2)O and Ca(4)(PO(4))(2)O. Hydroxyapatite formation is accompanied by an initial period of surface hydration of the precursors, an induction period, and a period during which the bulk of the conversion to hydroxyapatites occurs. The formation of SHAp occurred more rapidly in Hank's solution and distilled water than in serum. The formation of SHAp from these precursors is strongly inhibited by serum. There were two primary exothermal events associated with SHAp formation: initial heat evolution peak, which was associated with reactant dissolution, and the major heat evolution peak, which was associated with SHAp formation. The presence of the constitutents in serum depresses both. This is a result of serum macromolecules adsorbing onto the available surfaces regardless of whether they are reactants or products. Variations in heat evolution behavior, pH, and the times of disappearance of the reactants and appearance of SHAp correlate with one another.

Effect of synthesis temperature and doping level on conductivity and structure of poly(3-methyl thiophene).

Poly(3-methyl thiophene) was synthesized by oxidative chemical polymerization technique using ferric chloride as the dopant in an inert atmosphere. Samples of different doping levels were prepared and analyzed by Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy, and direct current (DC) conductivity measurement at room temperature (300 K). Synthesis of the polymer was confirmed by FTIR studies. FTIR spectra showed a shift in the heterocyclic bands in the region of 700-1200 cm(-1) with a decrease in synthesis temperature. It was evident from the scanning electron micrographs that the surface structure of the polymer became denser with an increase in doping level. The measured DC conductivity increased initially up to the doping level of 0.8 M and then this increase tended to slow down. Samples having a doping level of 0.4 M were synthesized at 300, 280, and 270 K while maintaining the other synthesis parameters. The conductivity and yield were found to increase as the temperature of the polymerization decreased.

Direct current conductivity studies on poly(3-methyl thiophene).

The direct current (DC) conductivity of poly(3-methyl thiophene) was measured in the temperature range of 77-300 K. The observed DC conductivity data were analyzed in the light of Mott's variable range hopping model. Different Mott's parameters such as characteristic temperature (T0), average hopping distance (R), average hopping energy (W), and density of states at the Fermi level (N [E(F)]) were evaluated. By taking the inverse of the coefficient of exponential decay of the localized states involved in the hopping process as 0.5 nm, a realistic value of density of states at the Fermi level (N [E(F)]) was obtained that agrees well with the values reported earlier for other conjugated polymers.