Aneta Hanc

A Study of Point Defects in the B2-Phase Region of the Fe–Al system by Mössbauer Spectroscopy

In this work, we employed the Mössbauer spectroscopy in a study of point defect formation in intermetallic phases of the B2 structure from the Fe-Al system as a function of Al concentration. We present the values of the 57Fe isomer shift and quadruple splitting for the components describing the point defect in the local environment of a Mössbauer nuclide. The concentration of the Fe vacancies and Fe atoms substituting Al (Fe-AS) are determined. The results shown that an increase in Al content causes an increase in vacancy and Fe-AS

X-Ray Investigations and Magnetic Properties of CuCr2-xSnxSe4 - Compounds

We have observed that doping CuCr2Se4 with tin introduces and then increases the tetrahedral deformation of the spinel structure, which can be connected with the Jahn-Teller (JT) distortion due to Cr2+ ions in antiprismatic environment. The presence of Cr2+ is corroborated by the increase of the saturation magnetization above the 6μB value expected for the 2 Cr3+ ions. In the high limit of the high Sn doping the deformation is decreased, which we attribute to elimination of the JT condition by the increased local distortions. With the tin doping the magnetic structure evolves from the ferromagnet, through spin-glass like to the antiferromagnetic due to increased AF coupling in the system. This is corroborated by the decreasing transition temperature and the Curie-Weiss parameter.

Influence of Manganese and Tin Substitution on the Structure and Magnetic Properties of CdCr2Se4

Single phase materials with general formula CdxMeyCr2Se4 (where Me = Mn, Sn) were obtained using solid state synthesis method. Both compounds are ferromagnets with TC =115K (Sn) and 135K (Mn). The values of Curie-Weiss parameter ΘC-W = 135K (Sn) and 145K (Mn) are higher than respective values of TC indicating a presence of competing antiferromagnetic component. The values of lattice parameters are consistent with Sn and Mn replacing Cd. Slight cadmium deficiency has been also observed.

Point Defect Study in Fe72Al28 Alloy as a Function of Thermal Treatment by Positron Lifetime Spectroscopy

The defect structure of Fe28Al samples is examined with the Positron Annihilation Lifetime Spectroscopy. The studies are carried out for samples in as-cast state and after heat treatments: annealing for 24 hours at 900°C (or 1050°C) and either slow cooling with furnace or quenching to oil. The PALS spectra are analyzed using two-state trapping model. Only one type of defects is detected. The positron lifetime in these defects (V) suggests that they are quenched-in Fe-monovacancies (VFe). The vacancy concentration strongly depends on the rate of cooling. Besides, V also depends slightly on the rate of cooling of the material. This fact suggests, according to the predictions of latest theoretical calculations, that V is sensitive to the atomic configuration in the nearest neighborhood of VFe, which give hope to estimate the degree of atomic ordering in alloys by the PALS technique.

Characterization of As-Cast Single-Crystal CMSX-4 Superalloy Turbine Blades

Nickel-based single-crystal superalloys are widely used for production of high pressure turbine blades. The studied blades were obtained in an ALD Vacuum Technologies furnace by the Bridgman technique. Crystallization process was carried out with drawing rates of 3 mm/min and 5 mm/min. The dendrite microstructure based on the γ/γ’ phases and their defects was characterized using X-Ray topography, Laue diffraction, transmission electron microscopy. The defect structure samples were examined with the positron annihilation lifetime spectroscopy. It was found that crystal orientation, lattice parameter of γ’ phase and concentration of defects are correlated. The defect concentration increases in some areas which was the result of deviation of the primary dendrite arm from crystallization direction . Only one type of point defects was detected.

Effect of Vacancies on Positron Annihilation and Hyperfine Interactions in Fe-Al Alloys - Ab Initio Study

Vacancies occupying different sub-lattices of D03 structure of Fe3Al alloy were investigated by the full potential linearized augmented plane wave method. The calculations basing on the super-cell approach have been performed for the vacancy concentrations of 1.6 and 3 at.%. For both concentrations the sub-lattice preference for vacancy location was determined. The dependence of vacancy formation energy on magnetic state of structure has been found. The positron lifetimes for the annihilation in the bulk (Fe3Al) and in vacancies have been investigated basing on the ab initio results for the electron density. The effect of vacancies on spin magnetic moment and hy-perfine parameters of Fe atoms neighboring the vacancy was examined. The results are discussed and compared with the data available.

The X-Ray Analysis and Mössbauer Studies Mn-V-Sn Alloys

The aim of the work is to search possibility for preparation of the Mn2VSn and V2MnSn Heusler-type compounds. We have carried out the 119Sn-Mössbauer spectroscopy, scanning electron microscopy and X-ray diffraction studies on the some Mn0.5V0.25 Sn0.25 and V0.5Mn0.25Sn0.25 solid solutions prepared by arc melting of the constituent metals. Combining an independent information about atomic structure from X-ray diffraction and Mössbauer spectroscopy it was possible to identify main chemical environments responsible for the magnetic ordering observed in the samples. The studies revealed that investigated alloys are characterized by existence of the binary compounds, namely V2Sn3, V3Sn and Mn3Sn, with different extension in Mn and V atomic concentration, respectively. No ternary compounds were found in investigated systems.

A Study of Point Defects in the B2-Phase Region of the Fe-Al System by Mössbauer Spectroscopy

In this work, Mössbauer spectroscopy and X-ray powder diffraction (XRD) are used in a study of point defect formation in intermetallic phases of the B2 structure of the Fe-Al system as a function of Al concentration. The results are compared with the concentrations of point defect determined from positron annihilation data. In the Mössbauer effect, two types of samples are investigated: Fe-Al alloys with few additives obtained by induction melting and Al-rich metallic powders produced by the self-decomposition method and intensive grinding of high energy in the electro-magneto-mechanical mill. The work presents the values of the 57Fe isomer shift and quadruple splitting for the components describing the point defect in the local environment of a Mössbauer nuclide. The concentration of the Fe vacancies and Fe atoms substituting Al (Fe-AS) are determined. The results show that an increase in Al content causes an increase in vacancy and Fe-AS concentration.