Structural, electric and dielectric properties of Ni0.5Zn0.5FeCoO4 ferrite prepared by sol-gel

Ni0.5Zn0.5FeCoO4 spinel ferrite was elaborated using sol-gel technique. X-ray diffraction patterns indicate that sample has a cubic spinel type structure with Fd-3m space group. The change in Raman modes and relative intensity were observed due to ball milling and consequently to the decrease of particle size and cationic redistribution. The Raman spectra show peaks appearing at 450 and 490 cm−1 corresponding to T2g (2) and T2g (3), respectively. It may be noted that both of these modes shift toward the higher wavenumber with the substitution of Zn by Ni in Ni0.5Zn0.5FeCoO4 ferrite. Mössbauer spectroscopy analysis shows one tetrahedral A-site and two octahedral B-sites. Due to Zn doping, the hyperfine magnetic fields are much smaller than for CoFe2O4 and NiFe2O4 ferrites. The Jonscher’s power low was used to describe the ac-conductivity measurements. Frequency dependence of dielectric constant (ε″) and tangent loss (tan) display a dispersive behavior at low frequencies that can be explained by the Maxwell Wagner model and Koop's theory. Electric modulus formalism has used to study the relaxation dynamics of charge carriers. The complex impedance spectra (Nyquist plots) show well-defined semicircles which are strongly dependent on the temperature.publishe

Influence of oxygen deficiency on optical and dielectric properties of La0.75Ba0.10Sr0.15FeO2.875-δ compounds

Using the conventional sol-gel process, the series of non-stoichiometric oxygen lanthanum ferrites with the formula 0.750.100.152.875 ― (δ=0.00, 0.125 and 0.25) were prepared. X-ray diffraction analysis confirmed the formation of the orthorhombic structure with Pnma space group. In the present work, we confirm the potential of 0.750.100.15 2.875 ― (δ=0.00, 0.125 and 0.25) as an efficient dielectric material. All samples show high absorbance in the visible region with wavelength above 300 nm. The optical band gaps are found to increase from 3.25 to 4.1 with increasing oxygen vacancy concentration. The dielectric constant, dielectric loss and loss factor were carried out as a function of oxygen vacancy concentration and frequency (102 -106 Hz) at room temperature. The variation of dielectric constant with frequency indicates dispersive behavior and giant dielectric response (more than 104 ) at low frequencies for compounds deficient in oxygen. Such value of makes ′ these samples an interesting material to be used in applications namely the reduction of electronic components size. To summarize, incorporating vacancy oxygen enhances the dielectric properties. Thus, the interesting dielectric constant and weak loss strengthen the use for potential applications.publishe

Investigating the structural, morphological, dielectric and electric properties of the multiferroic (La0.8Ca0.2)0.9Bi0.1FeO3 material

The (La0.8Ca0.2)0.9Bi0.1FeO3 (LCBFO) compound has been synthesized by the sol-gel method and characterized by X-Ray Diffraction (XRD), Scanning Electron Microscope (SEM), Raman spectroscopy and electrical impedance spectrometry. XRD results revealed that (La0.8Ca0.2)0.9Bi0.1FeO3 crystals are orthorhombic, belonging to the Pnma space group. The SEM measurements showed that the sample presents a large distribution of nano-grains connected to each other. The relaxation process and the electrical conductivity are awarded to the same type of charge carriers characterized by similar values of the activation energy determined from loss factor tangent tg δ( ), the imaginary part of the permittivity and from the Modulus spectrum. The ac-conductivity was analysed to examine the conduction mechanism, using the Jonscher’s universal power-law given by: = +σ ω σ Aω( )ac dc s. Based on the parameter s behavior, the conductivity was studied according to the NSPT model (non-overlapping small polaron tunneling).publishe

Iron(III) Complexes on a Dendrimeric Basis and Various Amine Core Investigated by Mössbauer Spectroscopy

Dendrimers of various generations were synthesized by the divergent method. Starting from various amine cores (G(0a), G(0b), G(0c)) the generations were built by reaction of the amine with acrylnitrile followed by hydrogenation with DIBAL-H. Treatment with salicylaldehyde creates a fivefold coordination sphere for iron in the molecular periphery. The resulting multinuclear coordination compounds are investigated by Mossbauer spectroscopy

Anomalous behavior of the Debye temperature in Fe-rich Fe-Cr alloys

Debye temperature, $\Theta_D$, of Fe-rich Fe$_{100-x}$Cr$_x$ disordered alloys with $0\le x \le 22.3$ was determined from the temperature dependence of the central shift of M\"ossbauer spectra recorded in the temperature range of 60 -- 300 K. Its compositional dependence shows a maximum at $x \approx 5$ with a relative increase of $\sim 30$% compared to a pure iron. The composition at which the effect occurs correlates well with that at which several other quantities, e. g. the Curie temperature and the spin-wave stiffness coefficient, $D_0$, show their maxima, but the enhancement of $\Theta_D$ is significantly greater and comparable with the enhancement of the hyperfine field (spin-density of itinerant $s$-like electrons) in the studied system. The results suggest that the electron-phonon interaction is important in this alloy system

Isothermal and Cyclic Aging of 310S Austenitic Stainless Steel

Unusual damage and high creep strain rates have been observed on components made of 310S stainless steel subjected to thermal cycles between room temperature and 1143 K (870 °C). Microstructural characterization of such components after service evidenced high contents in sigma phase which formed first from δ-ferrite and then from γ-austenite. To get some insight into this microstructural evolution, isothermal and cyclic aging of 310S stainless steel has been studied experimentally and discussed on the basis of numerical simulations. The higher contents of sigma phase observed after cyclic agings than after isothermal treatments are clearly associated with nucleation triggered by thermal cycling

Phase transformations of s-FeCr induced by ball milling

Abstract A tetragonal sigma phase s-Fe0.54Cr0.46 transforms gradually into a bcc phase by ball-milling in argon. Mssbauer spectroscopy shows further the presence of an amorphous phase. It starts to form after 25 h of milling in our experimental conditions

A technical note on the phase transformation in furnace container material after a periodic thermo-chemical treatment

The aim of this work is to investigate the metallurgical changes in the wall of cylindrical containers, fabricated by welding from AISI 310 steel, used in the thermal and chemical treatment of spindle chains for the automotive industry, for an in-service period of over 1000 h. In order to identify the phases originated during this in-service period, several etchants were used in the structural study, together with X-ray diffraction and 57Fe Mössbauer spectroscopy analysis. The metallographic technique demonstrates some limitations in the complete identification of the phases produced in the wall of the containers. The structure of the wall of the containers, after the referred to working period, is composed of an austenitic matrix, whose grain size is about 212 and 238 [mu]m, near the internal and external faces of the wall, respectively. These show numerous precipitates inside the grains and at the grain boundaries. The density of the precipitates decreases from the internal to the external surface. The precipitates are nitrides (Cr, Mo)12 (Fe,Ni)8-x N4-z near the internal surface, and carbides (Cr, Fe, Mo)23C6 on the other zones of the wall.http://www.sciencedirect.com/science/article/B6TGJ-4502Y49-G/1/4e6ae31d16e053b40c961bebbfda1e0