Papers by Barbara D . Sawicka
Materials Science and Engineering, Feb 1, 1985
The chemical composition of iron-containing droplets formed on the graphite tiles of the poloidal... more The chemical composition of iron-containing droplets formed on the graphite tiles of the poloidal ASDEX limiter after exposure to plasma discharges was analysed using 57Fe MOssbauer spectroscopy. Measurements in both transmission and conversion electron MiSssbauer spectroscopy modes indicate that iron is present predominantly in the form of an alloyed carbide phase of the cementite type (Fe, Cr, Ni)sC.
Journal of The Less Common Metals, 1987
cobalt moments. The magnitudes of the dysprosium moments are close to the free ion value, but tha... more cobalt moments. The magnitudes of the dysprosium moments are close to the free ion value, but that of cobalt, 1.2 p++ is smaller than the free ion value. At 295 K, the structure is still non-colinear, but all moments lie much closer to the c-axis. The dysprosium moments on nonequivalent sites are no longer parallel, their magnitudes are reduced to 6.4 and 6.6 pLB, respectively. The cobalt moment is reduced to 0.6 pfl and makes an angle of 192.6" with the c-axis.
Inorganic Chemistry, Jul 21, 2023
Physics Letters, Nov 1, 1976
Epitaxially grown iron oxide films have been studied microscopically by conversion electron M~ssb... more Epitaxially grown iron oxide films have been studied microscopically by conversion electron M~ssbauer spectroscopy. Specially designed proportional counters cover a temperature range between 1.75K and 1100K. A 5A-thick layer containing 5 7 Fe was grown at an arbitrary depth of a 5 6 Fe 3 0 4 film, evenat the topmost or at the interface with a substrate crystal, to find local properties nondestructively. Temperature dependence of the hyperfine parameters of Bi 3 Fe 5 0 1 2 films were analyzed to find structural and magnetic effects of Bi3+ in comparison with usual garnets. The Morin transition of a-Fe 2 0 3 was found to strongly depend upon the orientation of films and post-annealing.
Nuclear Instruments and Methods, Dec 1, 1975
Epitaxially grown iron oxide films have been studied microscopically by conversion electron M~ssb... more Epitaxially grown iron oxide films have been studied microscopically by conversion electron M~ssbauer spectroscopy. Specially designed proportional counters cover a temperature range between 1.75K and 1100K. A 5A-thick layer containing 5 7 Fe was grown at an arbitrary depth of a 5 6 Fe 3 0 4 film, evenat the topmost or at the interface with a substrate crystal, to find local properties nondestructively. Temperature dependence of the hyperfine parameters of Bi 3 Fe 5 0 1 2 films were analyzed to find structural and magnetic effects of Bi3+ in comparison with usual garnets. The Morin transition of a-Fe 2 0 3 was found to strongly depend upon the orientation of films and post-annealing.
Physics Letters A, Dec 1, 1977
The conversion electron Mössbauer spectra of 57Fe implants in silicon were measured in an applied... more The conversion electron Mössbauer spectra of 57Fe implants in silicon were measured in an applied strong magnetic field. The existence of axial, positive quadrupole coupling at iron nuclei was established.
Physica status solidi, May 16, 1977
J. SAWICKI (a), B. SAWICKA (b), and 0. GZOWSKI (c) Mossbauer spectra of 57Fe in iron-phosphate gl... more J. SAWICKI (a), B. SAWICKA (b), and 0. GZOWSKI (c) Mossbauer spectra of 57Fe in iron-phosphate glass are studied both in transmission (powder samples) and conversion electron reemission mode (pellets). Octahedrally coordinated ferrous and ferric ions are determined. The ratio FeZ+/Fe3+ is found to be strongly reduced near the surface of air-heated pellets, and reestablishes to the value about 0.4 after heat treatment of the samples in vacuum. Es werden MoBbauerspektren von 57Fe in Eisenphosphatglasern sowohl in Transmission (Pulverproben) als auch mit der Konversionselektronen-Reemissionsmode (Pellets) untersucht. Oktaedrisch koordinierte Ferro-und Ferriionen werden bestimmt. Es wird gefunden, daB sich das Verhaltnis Fe2+/FeS+ in der Nahe der Oberflliche der an Luft erhitzten Pellets stark verringert, wobei nach Temperung im Vakuum die Proben wieder den Wert von etwa 014 annehmen.
Mossbauer Spectroscopy is recently frequently applied to study the nature of defects in various m... more Mossbauer Spectroscopy is recently frequently applied to study the nature of defects in various materials as well as the behaviour of implanted atoms and the properties of implanted solids. The capacity of Mossbauer method in this application will here be discussed on the basis of selected examples.
Journal of Applied Physics, Dec 15, 1987
In order to explain the processes of metal deposition and dropletlike aggregation on graphite til... more In order to explain the processes of metal deposition and dropletlike aggregation on graphite tiles in tokamaks, we have studied thin iron films vapor deposited on graphite substrates by means of Mössbauer spectroscopy. It was found that after heating at 900 °C most of the iron has aggregated into small (submicron) droplets, similar to those formed on the surfaces of graphite limiters in tokamaks after prolonged exposure to plasma discharges. The Mössbauer spectra showed that the droplets consist of α-Fe, austenite γ-Fe, and cementite Fe3C. The results imply that the aggregation takes place in the solid phase, at temperatures significantly lower than the eutectic temperature of the Fe-C system. It is suggested that thin iron films on graphite investigated by Mössbauer spectroscopy can be sensitive probes for transient effects and radiation damage processes at the first wall in thermonuclear research.
Journal of Applied Physics, Dec 15, 1987
The microstructure and chemical composition of dropletlike deposits formed on the surface of grap... more The microstructure and chemical composition of dropletlike deposits formed on the surface of graphite limiters due to plasma discharges in the axis symmetric divertor tokamak experiment were analyzed using 57Fe Mössbauer transmission and conversion electron spectroscopy. It is found that the droplets consist mostly of alloy cementite, (Fe,Cr,Ni)3C, with an admixture of austenite smaller than ≂20%. The amount of cementite and the contribution of austenite depend considerably on the location of the deposits relative to plasma-drift direction, which reflects the varying conditions of metal and carbon redeposition and agglomeration in the tokamak chamber.
Journal de physique. Colloque, 1980
Nuclear Instruments & Methods in Physics Research Section B-beam Interactions With Materials and Atoms, May 1, 1987
Conversion electron Mossbauer spectroscopy is an attractive technique for near-surface exa~nat~on... more Conversion electron Mossbauer spectroscopy is an attractive technique for near-surface exa~nat~on of materials, which has great but as yet unexploited potential in plasma-wail interaction studies, as well as in other materials science elements of the fusion energy program. The CEMS technique has recently been applied for the first time in studying various companents of tokamaks, such as in first wall steels, graphite limiters and tritium breeding lithium ceramics. Studies of plasma-induced erosion and redeposition of iron in the ASDEX tokamak, agglomeration of alloy cementite particles on graphite limiters, modifications of iron and stainless steels under deuterium bombardment and analysis of iron impurities in lithium ceramics are presented here as examples.
Physica status solidi, Feb 16, 1972
A. Z. HRYNKIEW~CZ (a), A. J. PUST~WKA (b), B. D. SAWICKA (a), and J. A. SAWIGKI (b) Computer expe... more A. Z. HRYNKIEW~CZ (a), A. J. PUST~WKA (b), B. D. SAWICKA (a), and J. A. SAWIGKI (b) Computer experiments were performed t o find the distribution of the electric field gradients and the possible modifications of the Mossbauer spectra in very small crystalline particles. The calculations of EFG were made in point charge approximations for simple cubic and normal spinel lattices. Es wurden Computer-Experimente durchgefiihrt, um die Verteilung der elektrischen Feldgradienten und der moglichen Modifikationen von Mofibauerspektren in sehr kleinen kristallinen Teilchen zu finden. Die EFG-Berechnungen wurden in der Punktladungsnliherung fur einfache kubische und normale Spinellgitter durchgefiihrt.
Physics Letters, 1984
Conversion electron M6ssbauer spectra were measured for a series of amorphous dilute iron alloys ... more Conversion electron M6ssbauer spectra were measured for a series of amorphous dilute iron alloys obtained by implantation of 57Fe in Sc,
Hyperfine Interactions, 1983
Conversion electron Mössbauer spectroscopy has grown during the last decade as a new tool of surf... more Conversion electron Mössbauer spectroscopy has grown during the last decade as a new tool of surface science. High sensitivity, depth selectivity and capabilities of the method in non-destructive backscattering analysis are essential features of CEMS. These virtues made the method advantageous in various applications and stimulated considerable progress in experimental techniques. The latter is the subject of the present paper.
Nuclear Instruments & Methods in Physics Research Section B-beam Interactions With Materials and Atoms, Feb 1, 1990
We investigated the hyperfine interactions of "Fe ion, implanted Into diamond crystals that uere ... more We investigated the hyperfine interactions of "Fe ion, implanted Into diamond crystals that uere heated to X30 K during Implantation. The implantation of radioactive parent "Co ions w'as performed to a fluence of 2 X IO" Ions/en?. using the 50 kV isotope separator. The Miissbauer emission spectra were measured in the temperature range between 4 and 300 K, using a helium flow cryostat. About 2OF of the Implanted ions end up In high-symmetry (HS, presumably substitutional) sites. with the remaining 8047 of ions appearing in low-symmetry (LS presumably hexagonal interstitial) sites. The HS sites are characterized by very high Debye temperature Bt)-1300 K and by high s-electron density characteristic for Fe"+ (3d4rp3) electron configuration. Impurities at LS sites exhibit a Debye temperature of 550 k 50 K and a very large electric field gradient, KI = 1.2 x 10'" V/cm'. An anomalous rise of the recoil-free factor for LS sites below 100 K was observed. This effect can he an evidence of localized jumps of interstitial impurity atoms between adjacent tetrahedral and hexagonal positions In the host lattice. The \aIues of the s-electron densities and electric field gradtents at Fe nuclei implanted in diamond are compared with the correspondin g values in other IV-group matrices and are found to be correlated with the atomic volumes of the corresponding host element?.
Physica status solidi, Dec 16, 1979
B. D. SAWICKA (a), J. A. SAWICKI (b), J. STANEK (b), T. TYLISZCZAK (c), and J. KOWALSKI (b) Conve... more B. D. SAWICKA (a), J. A. SAWICKI (b), J. STANEK (b), T. TYLISZCZAK (c), and J. KOWALSKI (b) Conversion electron Mossbauer spectra of 3 atyo F e implanted in silicon and germanium are measured a t temperatures between 78 and 550 K. Helium counters of electrons are used in backscattering geometry. The results indicate a temperature-independent s-electron density at the iron nuclei. A rather small temperature dependence of the electric field gradient is observed and is interpreted in terms of the T3/2-relat)ionship. The possible location of iron implanted in amorphous silicon and germanium is discussed. E s u-erden die Elektronenkonversions-Moabauerspektren von 3 Atyo Fe, das in Silizium und Germanium implantiert wurde, bei Temperaturen zwischen 78 und 550 K gemessen. Heliumelektronenziihler werden in Ruckstreugeometrie benutzt. Die Ergebnisse zeigen eine temperat.urunabhangige s-Elektronendichte a m Eisenkern. Eine ziemlich kleine Temperaturabhangigkeit des elektrischen Feldgradienten wird beobachtet und mit der T3P-Beziehung interpretiert. Die mogliche Lokalisierung des implantierten Eisens in amorphem Silizium und Germanium wird diskut.iert.
Physica Status Solidi B-basic Solid State Physics, Sep 1, 1976
ABSTRACT
Physics Letters, Oct 1, 1981
ABSTRACT
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Papers by Barbara D . Sawicka