S. Stichleutner

Mössbauer study of metastable phase formation in vacuum deposited FeNiCr multilayers due to swift heavy ion irradiation

Abstract Conversion electron Mossbauer spectroscopy (CEMS) and X-ray diffraction (XRD) were used to study multilayers, consisting of a few atomic layers of iron, nickel and chromium with a composition 50%Fe–25%Ni–25%Cr, prepared by high vacuum deposition and subsequently irradiated by 246 MeV 86 Kr 8+ ions at room temperature. Metastable highly disordered microcrystalline ferromagnetic and paramagnetic phases have been detected in the Fe–Ni–Cr multilayers as a result of the swift heavy ion irradiation. These metastable phases never occur with thermally prepared alloys but are similar to those observed previously in the case of Fe–Ni–Cr alloys prepared by other non-equilibrium techniques as electrochemical deposition. The relative amount of these metastable phases increases with the irradiation fluence. It was shown that transformation of metastable phases into the stable ones occurs in high vacuum evaporated and ion beam mixed Fe–Ni–Cr films due to appropriate heat treatment in vacuum.

Mössbauer Investigation of Electrodeposited Sn–Zn, Sn–Cr, Sn–Cr–Zn and Fe–Ni–Cr Coatings

Abstract57Fe and 119Sn CEMS, XRD and electrochemical measurements were used to investigate the effect of the preparation parameters and the components on the structure and phase composition of electrodeposited Fe-Ni-Cr alloys in connection with their corrosion behavior. XRD of the electrodeposits reflect an amorphous-like character. 57Fe CEM spectra of Fe-Ni-Cr electrodeposited samples, prepared in a continuous flow plating plastic circulation cell with variation of current density, electrolyte velocity and temperature, can be evaluated as a doublet associated with a highly disordered paramagnetic solid solution phase. This phase was identified earlier in Fe-Ni-Cr electrodeposits that were prepared by another plating method and contained both ferromagnetic and paramagnetic metastable phases [1]. This is the first time that we have succeeded to prepare Fe-Ni-Cr alloys containing only the metastable paramagnetic phase. The effect of the plating parameters on the structure is also analysed by the quadrupole splitting distribution method. 119Sn CEM spectra of all Sn-containing plated alloys show a broad line envelop which can be decomposed at least into two components. One can be associated with β-tin. The other one can be assigned to an alloy phase. The structure and distribution of microenvironments of these phases depends on the plating parameters especially on the parameters of the reverse pulse applied.

Mössbauer and X-ray diffraction investigations of Sn-containing binary and ternary electrodeposited alloys from a gluconate bath

Constant current technique was applied to electrodeposit tin‐containing coatings such as tin‐cobalt (Sn‐Co), tin‐iron (Sn‐Fe) and a novel tin‐cobalt‐iron (Sn‐Co‐Fe) from a gluconate bath. The effect of plating parameters (current density, deposition time at an electrolyte temperature of 60°C and pH=7.0) on phase composition, crystal structure and magnetic anisotropy of alloy deposits has been investigated mainly by 57Fe CEMS, 119Sn CEMS and transmission Mossbauer Spectroscopy as well as XRD. 57Fe and 119Sn CEM spectra and XRD reflect that the dominant phases of the deposits are orthorhombic Co3Sn2, tetragonal FeSn2 or amorphous Fe‐Sn and amorphous Sn‐Co‐Fe in Sn‐Co, Sn‐Fe and Sn‐Co‐Fe coatings, respectively. Furthermore, the relative area of the 2nd and 5th lines of the sextets representing the magnetic iron containing phases decreases continuously with increasing current density in all Fe‐containing deposits. At the same time, no essential change in the magnetic anisotropy can be found with the plating t...

Mössbauer studies of the effect of swift heavy ion irradiation on electrodeposited Sn-Co-Fe coatings

57Fe and 119Sn conversion electron Mossbauer spectroscopy was used to study the radiation effect of 246 MeV Kr and 710 MeV Bi ions on electrochemically deposited amorphous Sn-Co-Fe coatings. The ion dependent changes induced by the swift heavy ion irradiation in the chemical short range order of these amorphous thin films regarding Fe and Sn atoms are discussed within the framework of the transient thermal spike model.

Mössbauer study of radiation effects on swift heavy ion irradiated Fe-Ni-Cr multilayers and electrodeposited alloys

57Fe conversion electron Mossbauer spectroscopy (CEMS) and X-ray diffractometry (XRD) were applied to study radiation effects on Fe-Ni-Cr electrodeposited alloys and vacuum deposited multilayers. As an effect of irradiation new sextet and doublet components appear in the CEM spectra of irradiated multilayers. They correspond to the highly disordered microcrystalline ferromagnetic and paramagnetic metastable phases formed in Fe-Ni-Cr alloys. Although these phases never occur in thermally prepared alloys, they are similar to those observed in electrodeposited Fe-Ni-Cr coatings of the same composition [1],[2]. The metastability of the phases was also shown by aging of the irradiated multilayers. Small but significant dose dependent changes were observed in the CEM spectra of irradiated electrodeposits existing in the form of amorphous or microcrystalline paramagnetic solid solution phase. This finding can be discussed in terms of irradiation induced change in the short range order and phase composition due to irradiation of the alloys.

Iron oxyhydroxide aerogels and xerogels by controlled hydrolysis of FeCl3·6H2O in organic solvents: stages of formation

Iron oxyhydroxide aerogels and xerogels were prepared by controlled hydrolysis of FeCl3·6H2O in organic solvents by using a limited amount of water or consuming solely water molecules available from the crystals. Ethanol, ethylene glycol, dimethyl sulfoxide (DMSO) and dimethyl formamide (DMFA) solvents were used, the hydrolysis was promoted with epichlorohydrin proton scavanger. High surface area aerogels were prepared by supercritical CO2 extraction of solvents, surface area and pore distribution measurements were performed on them. Aerogel and xerogel samples were characterized by XRD, Mossbauer spectroscopy and HRTEM methods. The process of hydrolysis was followed by recording Mossbauer spectra of frozen reaction mixtures. Stepwise progress and appearance of transient components were detected in DMSO and DMFA solvents. Aerogel samples exhibit asymmetric spectra with low probability of Mossbauer effect in their as synthesized state. In contrast, frozen reaction mixtures, gels, dry xerogels and compressed aerogels display symmetric spectra with high probability of the Mossbauer resonance. XRD proves the dominant presence of 2-line ferrihydrite. HRTEM studies reveal 4–8 nm typical particle sizes with 0.21–1.0 nm characteristic lattice distances. Different types of coordination environments are distinguished for iron in the formed ferrihydrite nanoparticles due to structural features and imperfections.