M. Siddique

Enhancement in the multiferroic properties of BiFeO3 by charge compensated aliovalent substitution of Ba and Nb

Polycrystalline ceramics, Bi1-2xBa2xFe1-x Nb xO3 (x = 0.00–0.15), were synthesized by solid state reactions method. X-ray diffraction data have revealed elimination of impurity phases and an increase in unit cell volume with Ba and Nb substitution. Diffraction peak splitting is found to be suppressed which indicates a decrease in octahedral distortion. The Mossbauer spectra demonstrate the suppression of spiral spin modulation of the magnetic moments resulting in enhanced ferromagnetism with increasing dopant concentration. The leakage current density of the sample with x = 0.10 is found to be greatly reduced up to six orders of magnitude as compared to the undoped sample. Ohmic conduction is found to be dominant mechanism in all the samples, however, undoped sample showed space charge limited conduction in high electric filed region, while the sample with x = 0.15 exhibited grain boundary limited conduction in low electric field region.

Colossal resistivity with diminished tangent loss in Zn?Ni ferrite nanoparticles

We have investigated the electrical and magnetic response of the sol‐gel synthesized ZnxNi1−xFe2O4 (x = 0.0, 0.5 and 1) nanoparticles. The ratio of A-site sextet intensity to that of B-site sextet is featured in terms of divergence in coordination of Fe 3+ ions from four-fold (A-site) to six-fold (B-site). Canted spin structure and weakening of Fe 3+ (A)‐Fe 3+ (B) interactions at the surface of the nanoparticles assign the reduced value of room temperature magnetization in these nanoparticles. Shift of the blocking temperature with Zn content is ascribed to the change in the magnetic anisotropy. Colossal resistivity and reduced dielectric constant are discussed on the basis of dangling bond, superparamagnetic character, canted spin structure and polarizability of the cations. Diminished tangent loss is stipulated in terms of decrease in magnetocrystalline anisotropy and collapse of long-range magnetic order. We report colossal resistivity (i.e. 3.15 × 10 9 � cm), reduced dielectric constant (3.97) and diminished tangent loss (0.07) for Ni0.5Zn0.5Fe2O4 nanoparticles. (Some figures in this article are in colour only in the electronic version)

Investigation on the structural, dielectric and impedance analysis of manganese substituted cobalt ferrite i.e., Co1−xMnxFe2O4 (0.0 ≤ x ≤ 0.4)

Manganese substituted cobalt ferrites, i.e., Co1−xMnxFe2O4 (0.0 ≤ x ≤ 0.4) were prepared by a solid state reaction method. XRD analysis confirmed the formation of a single-phase cubic spinel structure for all of the synthesized compositions, whereas an SEM study revealed that Mn substitution changes the microstructure. 57Fe Mossbauer spectroscopy measurements suggested that Fe3+ cations progressively migrate with Mn addition from tetrahedral (A) sites to octahedral (B) sites which have a relatively smaller covalency. Therefore, the distribution of cations between the A- and B-sites changed with increasing x. Moreover, interestingly, the Fe2+/Fe3+ cation ratio remains zero and high spin Fe3+ is the only oxidation state observed at both sites for all of the synthesized compositions. In order to explore the effects of observed variations in the microstructure and cation distribution on the dielectric and resistive properties, the prepared samples were subjected to impedance spectroscopic experiments in a wide frequency range at room temperature. Mn substitution is found to improve the resistive properties by about two orders of magnitude. This increase in the resistive properties is explained in terms of the variations in the microstructure and decrease in the mobility of the charge carriers associated with the cations redistribution. Similarly, the variation in the dielectric permittivity is also conferred in terms of the change in microstructure and cation redistribution.

Isochronal crystallization of metglass Fe83B17 using Mössbauer effect and resistivity measurements

Abstract Mossbauer effect and resistivity measurements indicate three stages of crystallization in iron-boron metglass Fe 83 B 17 . During the structural relaxation stage (300–625K), the incipient crystallization produces a boron-rich FeB phase. In crystallization region (625–660K) α-Fe and t-Fe 3 B phases are produced. In structure coarsening stage (660–925K) the production of o-Fe 3 B and Fe 23 B 6 takes place. o-Fe 3 B phase is found to be a stable while t-Fe 3 B is a metastable phase.

Composition Dependence of Quadrupole Splitting in Cd—Zn Ferrites

The composition dependence of quadrupole splitting (QS) in Zn-substituted Cd-ferrites has been investigated using the Mossbauer effect measurements. Mossbauer spectra of 57 Fe in Cd 1-x Zn x Fe 2 O 4 (x = 0, 0.25, 0.50, 0.75, 1.0) ferrite systems were taken at room temperature. It is found that both calculated and experimental values of QS vary linearly with the increase of Zn 2+ cations and also have a good agreement between themselves. The isomer shift (IS) for all probable site occupancies remains the same in all compositions.

Mössbauer study of corrosion of mild steel induced by acid rain

Room temperature corrosion studies have been made on the rust of commercially available mild steel in a simulated acid rain environment using the method of transmission Mössbauer spectroscopy. The main corrosion products identified are α-FeOOH, γ-FeOOH, and a product with unfamiliar parameters which seems to be amorphous in nature (being very large linewidth −2.5 mm/s) and may be considered as an intermediate phase. A small amount of γ-Fe2O3 (6–8%) is also observed.

Phase transition in melt-spun Fe88B12 and Fe72B28 alloys by resistivity measurements and Mössbauer spectroscopy

Abstract Resistivity measurements and Mossbauer spectroscopy indicate that the as-quenched Fe 88 B 12 and Fe 72 B 28 melt-spun alloys are not completely crystallized. This is not in agreements with the earlier observations on the same alloys by DTXD measurements. In as-quenched Fe 88 B 12 α-Fe, o-Fe 3 B and amorphous phases are found while in Fe 72 B 28 the phases found are α-Fe and t-Fe 3 B. The phases o-Fe 3 B and t-Fe 3 B are metastable while t-Fe 2 B is stable upto 825K.

Iron–manganese–titanium (1 : 1 : 2) oxide composite thin films for improved photocurrent efficiency

In continuation of our previous studies on the photoelectrochemical (PEC) properties of titanium-based composite oxide thin films, an effort was made to develop thin films of the 1 : 1 : 2 iron–manganese–titanium oxide composite, Fe2MnTi3O10–MnTiO3, using Fe(OAc)2 and a bimetallic manganese–titanium complex, [Mn2Ti4(TFA)8(THF)6(OH)4(O)2]·0.4THF (1), where OAc = acetato, TFA = trifluoroacetato, and THF = tetrahydrofuran by the aerosol-assisted chemical vapour deposition (AACVD) technique. The thin films after their proper characterization with X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Mossbauer spectroscopy, field emission scanning electron microscopy (FESEM), atomic force microscopy (AFM), energy-dispersive X-ray (EDX) spectroscopy, UV-Vis spectrophotometery and photoluminescence (PL) spectroscopy were tested for their potential applications for the photoelectrochemical oxidation of water. The PEC results revealed that a photocurrent density (Jlight) of 1.88 mA cm−2 was obtained at a low potential of 0.20 V vs. Ag/AgCl/3MKCl inferring a promising photo-conversion efficiency of 1.56%. These observations were further endorsed by electrochemical impedance spectroscopic (EIS) studies in terms of charge transportation and its recombination time. Furthermore, the Mott–Schottky plot indicated a flat band potential of −1.0 V vs. Ag/AgCl.

Mössbauer study of corrosion of SS-304 exposed to sea water

Mössbauer study of the rust formed on SS-304 exposed to sea water for about 30 d indicates that ferrihydrite and β-FeOOH are formed as corrosion products, the cause of corrosion being the presence of chloride ions in sea water. Ferrihydrite is found to exhibit two doublets at 300 K while at 80 K it exhibits a doublet and a sextet. This is contrary to earlier studies in which it was reported that at 80 K ferrihydrite is fully magnetically ordered and exhibits a sextet only.

Temperature factor of silicon by powder neutron diffraction

The temperature factor of silicon has been determined by the powder neutron diffraction technique employing a double-axis neutron diffractometer. A neutron wavelength of 1.184 A was used in the experiment. The sample used was a fine powder of silicon of purity 99.999%. The correction to the observed intensities due to thermal diffuse scattering (TDS) was not applied as the neutron velocity of 3.34 km s-1 (corresponding to neutron wavelength of 1.184 A) is less than the minimum velocity of sound in this crystal. The B value obtained from these experiments was found to be 0.45 (2) A, corresponding to a mean-square vibrational amplitude of 0.017 (2) A2 and to a Debye temperature of 531 (11) K at the sample temperature of 284 K at which the experiment was performed.