Theoretical and Mossbauer effect study of magnetic and elektonic properties of Fe3AL compound

The electronic properties of Fe3Al were determined experimentally, with the use of the Mössbauer spectroscopy, and theoretically. The band structure of the compounds was investigated applying the self-consistent tight-binding linear muffin tin orbital method. The calculated Fermi contact term of hyperfine fields and the isomer shifts are in good agreement with the values resulting from analysis of experimental data. The different kinds of electron transfer estimated on the base of the proposed "additive model" are also strongly supported by calculations

A Mossbauer and structural study of disordered alloys Fe3-xTixAl (0 x 1)

A series of the disordered Fe3−xTixAl (x = 0, 0.2, 0.45, 0.55, 0.65, 0.70, 0.75, 1) alloys obtained by arc-melting were studied. Directly after melting the samples were mechanically crashed and in that form examined by the structural and Mössbauer effect methods. The alloys were strongly disordered, but it was possible to identify, apart from Fe-bcc phase, the origins of forming such phases as Fe2TiAl Heusler phase, Fe3Al with DO3 structure, FeAl and FeTi with B2 structure and non-stechiometric Fe2Ti Laves phase with hexagonal C14 structure. For Ti concentration up to x = 0.45, the disordered Fe-bcc phase dominates. For Ti concentration from x = 0.55 to x = 1, the Fe2TiAl phase coexists with FeAl phase (for x = 0.55, 0.65) and with FeTi phase (x = 0.7 and 0.75). In a sample with the nominal Fe2TiAl composition of Fe2TiAl Heusler phase, a non-stoichiometric Fe2Ti Laves phase with hexagonal C14 structure was observed

Defect structure of Fe-Al and Fe-Al-X (X=Ni; Cu; Cr) metallic powders obtained by the self-decomposition

In the present work, the Fe-Al-X (X = Cu; Ni; Cr) metallic powders produced by the self-decomposition method of the Fe-Al doped alloys were examined by Mössbauer spectroscopy. The concentration of the Fe vacancies and the Fe atoms substituting Al (Fe-AS) was determined from the intensities of the sub-spectra in the Mössbauer analysis connected with distinct Fe environments. The results have shown that nickel and copper cause an increase of vacancy concentrations in comparison with the values found for Fe-Al metallic powders, whereas chromium decreases vacancy concentrations causing a significant increase of anti-site atoms Fe-AS concentration

Positron-annihilation study of aging effects in the Cu-Zn-Sn parent phase

A study of ageing effects on the structure of Cu-Zn—Sn shape memory alloys was performed using the 119 Sn Mössbauer spectroscopy and positron annihilation techniques (the positron lifetime, and Doppler broadening lineshape S-parameter measurements). Two stages of ageing at 200°C connected with redistribution of Sn atoms were observed

Structure and magnetic properties of amorphous and nanocrystalline Fe85.4Hf1.4B13.2 alloy

Purpose: The forming of magnetic properties of the nanocrystalline Fe-based are different than those in conventional ferromagnetic materials that is: the soft magnetic properties increase with decreasing of grain size of crystalline phase Design/methodology/approach: The nanocrystalline Fe-based alloys could be obtain by many different methods, in this work first amorphous ribbons were obtained by planar-flow casting method and after that amorphous precursor were heat treated. The changes of structure associated to crystallization was investigated by X-ray diffractometry, the analysis of Mössbauer spectra made it possible to determine the average hyperfine field and volume fractions of α Fe crystalline phase. The changes of coercive force (Hc) of tapes were investigated using coerciometer with the terrestrial magnetic field compensation. Findings: The obtained results of investigations shows that crystallization process of amorphous Fe85.4Hf1.4B13.2 allowed to form nanocrystalline structure. This crystallization process has two-stages character and exhibit redistribution of the phases stages. The changes of magnetic properties has been observed with increasing the temperature annealing of investigated alloy. The coercive force is decreasing and minimum Hc is obtained at temperature 523 K. The obtained results showed clearly that for examined alloy is possible to determine the specific thermal treatment conditions (Top) causing an improvement of the magnetic properties. Practical implications: The possibility of optimization of soft magnetic properties is obtaining by the use of controlled crystallization of amorphous alloys. Originality/value: It has been found that the Fe85.4Hf1.4B13.2 alloys consisting of a mostly single bcc structure with nanoscale grains exhibit much better soft magnetic properties than in example well-known nanocrystalline Fe73.5Cu1Nb3Si13.5B9 . The group of Fe – M – B alloys is called NANOPERMTM. From a viewpoint of industrial application they are very attractive materials especially because of the highest BS among the nanocrystalline alloy

Defect structure of Fe-AL and Fe-Al-Ni metallic powders obtained by the self-decomposition method and intensive grinding in the electro-magneto-mechanical mill

The Fe-Al and Fe-Al-Ni metallic powders produced by the self-decomposition method and then intensive grinding in an electro-magneto-mechanical mill with Fe and Ni additions were examined by X-ray powder diffraction, scanning electron microscopy and Mössbauer spectroscopy. The concentration of vacancies and Fe atoms occupying Al positions (Fe-AS atoms) was determined from the Mössbauer spectra analysis connected with distinct Fe environments. The results show that nickel addition causes both an increase in vacancy concentrations in comparison with values found for Fe-Al metallic powders and a significant increase in the antisite Fe-AS atoms concentration. Intensive highenergy grinding in the electro-magneto-mechanical mill modifies the phase composition of the studied materials and changes the concentration of point defects

Positron annihilation lifetime in situ study of deformed polyolefin elastomers

The positron annihilation lifetime spectroscopy was used to investigate the free volume hole size of ethylene octane copolymers as a function of deformation in the range from 0 to 110% in steps of 10%. For each degree of deformation a series of 5-6 positron annihilation lifetime spectra was collected in situ. All spectra of a given series were analysed simultaneously. They were resolved into three exponential components, of lifetimes parameters ¿i and intensities Ii. The variations of ¿3 reflect three deformation regions, the elastic range, strain softening range, and plastic region

57Fe Mossbauer spectroscopy of annealed metamict davidite

This paper reports preliminary results of 57Fe Mössbauer spectroscopy and X-ray diffraction (XRD) studies of metamict davidite samples (La,Ce,Ca,Th)(Y,U,Fe)(Ti,Fe,Mn)20(O,OH)38 after high temperature annealing in an argon atmosphere. The Mössbauer spectra show a gradual decrease of quadrupole splitting and line width values of an Fe3+ doublet with increasing annealing temperature. Rather unexpected feature of these spectra for an Fe2+ doublet is a considerable increase of the line width with progressive crystallinity and a simultaneous decrease of both quadrupole splitting and isomer shift values. Changes of the hyperfine parameters as a function of the annealing temperature appeared as sensitive indicators of the thermal recrystallization process of metamict davidite similar to metamict silicates

First principles study of the isomer shift in Fe44M6Al50 (M=Ti,V,Cr,Co,Ni,Cu) alloys with B2 structure

The 57Fe isomer shift for Fe44M6Al50 intermetallics with the B2 structure doped with M = Ti, V, Cr, Co, Ni and Cu additions has been calculated with the tight-binding linear muffin-tin orbital (TB-LMTO) method. The effect of variation of Wigner-Seitz (WS) spheres radii on the calculated equilibrium lattice parameter (a) and isomer shift (IS) was analyzed. The calculations have shown that the 57Fe isomer shift in Fe44M6Al50 intermetallics is directly proportional to the changes in the local 4s electronic charge at Fe atoms involved by M addtions. The screening effect of 4s electrons due to changes in (4p + 3d) electronic charge is of secondary importance. The calculated dependence of the average IS on nuclear charge (Z) of the alloying metal (M) follows qualitatively the tendency observed experimentally for the M impurities in the Fe host

Ab initio study of the effect of pressure on the hyperfine parameters of Fe57 in bcc phase

In this paper the results of studies on the effect of pressure on hyperfine magnetic field (Bf) and isomer shift (IS) for Fe-bcc are presented. Two calculation methods were used: TB-LMTO (Tight Binding Linear Muffin-Tin) and FP-LAPW (Full Potential Linearized Augmented Plane Wave) and the obtained results have been compared. Both methods lead to comparable results. In the study a particular emphasis has been laid on investigations of the atomic core electrons (1s, 2s, 3s) and of the conduction electrons 4s on the Bf and IS values. The calculated values of the dIS/dlnV and dlnB /dlnV parameters give evidence of good conformity with those derived from experimental data