Variation of structural and hyperfine parameters of (Fe0.70Al0.30) 1-xNbx , with x=0, 0.05, 0.10 and 0.20 System

Fe0.70Al0.30 alloy is a bcc and ferromagnetic phase, being the Al atoms magnetic dilutor. In this work, we study the effect of the Nb on the structural and hyperfine behavior of the Fe0.70Al0.30 alloy when atoms of Nb substitute atoms of Fe or Al. The nanostructured system of (Fe0.70Al0.30)1-xNbx (x = 0, 0.05, 0.10, 0.20, at. %) was obtained by alloying Fe, Al and Nb powders in a planetary ball mill during 12 h, 24 h and 36 h, and a ball mass to powder mass relation of 10:1. The magnetic and hyperfine properties of the samples were studied by X-ray diffraction (XRD) and Mössbauer Spectrometry (MS) at room temperature, respectively. The X-ray diffraction patterns for x=0 showed the bcc-α FeAl structure and its lattice parameter is approximately constant with milling times (∼ 2.91 Å). For x=0.05, 0.10 and 0.20 the patterns showed the coexistence of the α-FeAl, Nb(Fe,Al)2 structural phases with an amorphous component. The Mössbauer spectra of x=0 samples were fitted using hyperfine magnetic field distributions (HMFDs), and the obtained mean hyperfine fields (MHF) were 23.4, 24.2, and 24.3 T for 12, 24, and 36 h of milling time, respectively, which correspond to the α-FeAl structure. The spectra of the samples with x=0.05 and 0.10 were fitted using a model with two components, the first one is a HMFD attributed to the bcc-FeAlNb structure and the second with two doublets attributed to the Nb(Fe,Al)2 structure. When atomic percentage of Nb increases up to 20 at. % the ferromagnetic behavior is diluted due to substitution of Fe-atoms by Nb and Al atoms in the bcc-FeAlNb structure. The magnetic behavior becomes paramagnetic at x=0.20, the spectra were fitted with three doublets, one of them related with bcc-FeAlNb structure and the others to the Nb(Fe,Al)2 structural phase. The alloying of Nb to the Fe0.70Al0.30 system destroyed the magnetism due the substitution of Fe by Nb atoms and generates an amorphization into the syste

Structural and magnetic properties of FeCoC systemobtained by mechanical alloying

Fe96−xCoxC4 (x = 0, 10, 20, 30, 40 at. %) alloys were obtained by mechanical alloying of Fe, C and Co powders using high-energy milling. The structural and mag- netic properties of the alloy system were analyzed by X-ray diffraction, Scanning Electron Microscopy (SEM), Vibrating Sample Magnetometer (VSM) and Mossbauer Spectrome- ̈ try at room temperature. The X-ray diffraction patterns showed a BCC-FeCoC structure phase for all samples, as well as a lattice parameter that slightly decreases with Co content. The saturation magnetization and coercive field were analyzed as a function of Co content. The Mossbauer spectra were fitted with a hyperfine magnetic field distribution showing the ̈ferromagnetic behavior and the disordered character of the samples. The mean hyperfine magnetic field remained nearly constant (358 T) with Co content

Solid state synthesis of Bi0.4Sr0.6FeO3 powder for SOFC applications

We report on the synthesis of Bi0.4Sr0.6FeO3 powder with cubic structure by solid state reaction (mechanical milling and calcination) from Bi2O3, SrCO3 and Fe2O3 stoichiometric ratios. Milled powder mixtures were heat treated between 775∘C and 825∘C for 30 and 60 min in oxygen atmosphere and characterized by X-ray diffraction (XRD), impedance as well as Mössbauer spectroscopy. The cubic phase of Bi0.4Sr0.6FeO3 was successfully obtained in samples milled for only 2 h and a subsequent calcination at 800∘C. Irrespective of milling time, heat treatments at lower temperatures (775∘C) still show spurious phases such as Sr0.23Bi0.76O1.1 (30 min) and Sr0.53Bi1.72O3 (60 min). Impedance spectroscopy show high values (105–109) Ω indicating strong structural bond between the atoms of the system and activation energies for the strontium ion around 04 eV. These results show a single dynamic behavior in a range from 1 to 2*105 Hz enabling data adjustment and analysis to a RC circuit. Conductivity results normally show a behavior that obeys the universal law of Jonscher’s relaxation (σ = σ Dc + α ω n) with values for the exponent n (0.8 < n < 1) typical in these structures. Mössbauer spectrometry measurements reveal that the hyperfine magnetic field of the precursors and milled powders corresponds to hematite 512 T. After the thermal treatment of the samples, the mean hyperfine field decreases to 489 ± 0.5 T showing the Bi and Sr atoms diffusion, (non- magnetic) in Fe2O3. While the result of isomer shift corresponds to a Fe+3 oxidation state irrespective of the heat treatmen