The complex Mössbauer spectra exhibited by FexO (x≈0.91) and (Fe1−yMg y )xO (y=0.15−0.85) powder samples at liquid helium temperature have been analysed by a Hamiltonian treatment to allow for the significant electric field gradients present at the Fe2+ defect sites. The magnetic behaviour of the defect clusters are considered in terms of antiferromagnetic couplings, consistent with the spin glass-like behaviour reported recently for magnesiowüstite.

LiTaO3 single crystals were doped with57Co. Heat treatments of the crystals in the various atmospheres (Ar, Ar/H2 etc.) very sensitively influenced the charge states of iron formed after the EC of57Co. Fe2+ Fe3+ and metallic clusters are formed depending on the treatments in the various atmospheres. The observed effects were found reversible by changing the reducing and oxidising atmospheres.

Topotactic proton exchange (Li against H) can be achieved by treating LiBnO3 with appropriate acids. In order to investigate the effect of proton exchange on Fe-impurities we studied LiNbO3:Fe powder material treated in sulphuric acid and LiNbO3:Fe single crystals treated in benzoic acid by Mössbauer spectroscopy. During the topotactic ion exchange only the Li-ions are exchanged for protons, whereas the Fe-impurities are retained in the material.

Fe nanocrystals (particles with a size of some nanometers) were prepared by the inert-gas condensation method with subsequent oxidization. The average size of the particles in the thin oxide layer was determined to be about 30 Å. The samples were studied by Mössbauer spectroscopy at various temperatures. Superparamagnetism seems to be suppressed in these samples. Furthermore, a two-stage decrease of the average hyperfine field was observed in the oxide layer. The Fe oxide-Fe interface anisotropy is proposed to be responsible for this phenomenon.

Samples of the system LiNbO3-Fe2O3 prepared by water quenching and by the double-roller quenching method in the range up to 24 mol% Fe2O3 were investigated by Mössbauer and ESR spectroscopy. In the water quenched samples up to 11 mol% Fe2O3 only the Fe3+ and the Fe2+ valence states could be detected. The Fe2+ concentration decreased with increasing Fe2O3 content. Above 11 mol% Fe2O3 magnetically split Mössbauer spectra indicated the presence of Fe2O3 clusters. The isomer shift values of Fe3+ as a function of Fe2O3 concentration showed jumps at 6 and 11 mol% Fe2O3, whereas no significant changes could be detected in the quadrupole splitting values. The ESR data already exhibited the existence of isolated Fe3+ ions and of clusters with Fe-Fe distances less than 8 Å for the lowest Fe2O3 concentration. The cluster signal intensity increased with increasing Fe2O3 content. The roller quenched samples showed increased Fe2+ concentration as compared to the water quenched samples, which suggests that slow quenching results in iron oxidation and cluster formation. For low Fe2O3 concentrations a valence state change Fe3+⇄Fe2+ can easily be obtained by heat treatments in various atmospheres, whereas for higher Fe2O3 contents (9.8 mol%) precipitations ofα-Fe (in reducing atmosphere) and Fe2O3 (in air) could be observed in addition to the valence state changes of a remaining part of dissolved Fe ions. On the basis of the obtained results a model was suggested for the unusual behaviour of the lattice parameters observed in LiNbO3-Fe2O3.

The ferroelectric phase transition in LiNbO3: Fe has been investigated by means of Mössbauer spectroscopy. The recoilless fraction of the γ-rays showed a strong anisotropy, reflecting large amplitudes of the Fe-ions along the hexagonal c-axis. Since a strong coupling of the Fe2+-ions to the Li-sublattice could be proved, the observed behaviour of the Fe cations supports the model proposed by Abrahams et al. [1], according to which above Tc, the Li-ions occupy equivalent non-centrosymmetric sites on either side of the oxygen ion planes with equal probability, while the Nb-ions shift to centrosymmetric positions.

physica status solidi (a)Volume 105, Issue 1 p. 219-230 Original Paper A comparative study of impurity defects in crystalline and amorphous LiNbO3 H. Engelmann, H. Engelmann Fachbereich Angewandte Physik der Universität des Saarlandes, Saarbrücken Search for more papers by this authorW. Gatzweiler, W. Gatzweiler Fachbereich Angewandte Physik der Universität des Saarlandes, Saarbrücken Search for more papers by this authorI. Dézsi, I. Dézsi Fachbereich Angewandte Physik der Universität des Saarlandes, Saarbrücken On leave from Central Research Institute for Physics, Budapest.Search for more papers by this authorU. Gonser, U. Gonser Fachbereich Angewandte Physik der Universität des Saarlandes, Saarbrücken Search for more papers by this author H. Engelmann, H. Engelmann Fachbereich Angewandte Physik der Universität des Saarlandes, Saarbrücken Search for more papers by this authorW. Gatzweiler, W. Gatzweiler Fachbereich Angewandte Physik der Universität des Saarlandes, Saarbrücken Search for more papers by this authorI. Dézsi, I. Dézsi Fachbereich Angewandte Physik der Universität des Saarlandes, Saarbrücken On leave from Central Research Institute for Physics, Budapest.Search for more papers by this authorU. Gonser, U. Gonser Fachbereich Angewandte Physik der Universität des Saarlandes, Saarbrücken Search for more papers by this author First published: 16 January 1988 https://doi.org/10.1002/pssa.2211050123Citations: 11 D-6600 Saarbrücken, FRG. AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Abstracten Crystalline LiNbO3:Fe, LiNbO3:Fe:Mn, and amorphous LiNbO3:Fe are investigated by using the Mössbauer effect. Information on valence states and structural surroundings of iron impurities is obtained. Valence state changes can be achieved by heat treatments in different atmospheres for both phases. In crystalline LiNbO3 partial conversion of the valence states of Fe is also obtained by irradiating the samples with appropriate wavelengths from a high-pressure Hg lamp. The optically induced valence state changes of Fe ions are interpreted according to the model proposed by von der Linde et al. and Schirmer and von der Linde. Abstractde Kristallines LiNbO3:Fe, LiNbO3:Fe:Mn und amorphes LiNbO3:Fe werden mit dem Mößbauereffekt untersucht. Informationen über Valenzzustände und strukturelle Umgebung von Eisenstörstellen werden erhalten. Valenzzustandsänderungen lassen sich durch Wärmebehandlung in verschiedenen Atmosphären für beide Phasen erhalten. In kristallinem LiNbO3 wird eine teilweise Konversion des Valenzzustandes von Fe auch durch Bestrahlung der Proben mit Licht geeigneter Wellenlängen von einer Hg-Hochdrucklampe erhalten. Die optische induzierten Valenzzustandsänderungen der Fe-Ionen werden entsprechend dem von von der Linde et al. und Schirmer und von der Linde vorgeschalagenen Modell interpretiert. References 1 D. von der Linde and A. M. Glass, Appl. Phys. 8, 85 (1975). 2 E. Krätzig and R. Orlowski, Appl. Phys. 15, 133 (1978). 3 A. M. Glass, D. von der Linde and T. J. Negran, Appl. Phys. Letters 25, 133 (1974). 4 S. C. Abrahams, J. M. Reddy and J. L. Bernstein, J. Phys. Chem. Solids 27, 997 (1966). 5 A. M. Glass, M. E. Lines, K. Nassau and J. W. Shiever, Appl. Phys. Letters 31, 249 (1977). 6 A. M. Glass, K. Nassau and T. J. Negran, J. appl. Phys. 49, 4808 (1978). 7 H. S. Chen and C. E. Miller, Rev. sci. Instrum. 41, 1237 (1970). 8 V. I. Coldanskii and R. H. Herber (Ed.), see, for example Mössbauer Spectroscopy Academic-Press, New York 1968. 9 W. Keune, S. K. Date, I. Dézsi and U. Gonser, J. appl. Phys. 46, 3914 (1975). 10 V. N. Belogurov and P. E. Senkov, Appl. Phys. 21, 195 (1980). 11 W. Gatzweiler, Diplomarbeit, Universität des Saarlandes, Saarbrücken 1984. 12 J. H. Terrell and J. J. Spijkerman, Appl. Phys. Letters 13, 11 (1968). 13 D. von der Linde, O. F. Schirmer and H. Kurz, Appl. Phys. 15, 156 (1978). 14 O. F. Schirmer and D. von der Linde, Appl. Phys. Letters 33, 35 (1978). 15 E. M. Gyorgy, K. Nassau, M. E. Eibschütz, J. V. Waszczak and C. A. Wang, J. appl. Phys. 50, 2883 (1979). 16 H. Engelmann, W. Gatzweiler, U. Gonser, I. Dézsi and A. Balogh, J. non-crystall. Solids 89, 326 (1987). 17 A. Hero, U. Gonser, H. Engelmann and H. J. Hagemann, Ferroelectrics 65, 211 (1985). 18 M. Blume, Phys. Rev. Letters 14, 96 (1965). 19 S. Mørup, Paramagnetic and Superparamagnetic Relaxation Phenomena Studied by Mössbauer Spectroscopy, Polytechnisk Forlag, Lyngby 1980. 20 R. R. Sharma, T. P. Das and R. Orbach, Phys. Rev. 149, 257 (1966). 21 M. G. Clark, F. J. Di Salvo, A. M. Glass and G. E. Peterson, J. chem. Phys. 59, 6209 (1973). 22 A. Zylbersztejn, Appl. Phys. Letters 29, 778 (1976). 23 F. Urbach, Phys. Rev. 92, 1324 (1953). 24 J. D. Dow and D. Redfield, Phys. Rev. B 5, 594 (1972). 25 D. L. Staebler and W. Phillips, Appl. Phys. Letters 24, 268 (1974). Citing Literature Volume105, Issue116 January 1988Pages 219-230 ReferencesRelatedInformation

Solid-solid surface adsorption of Eu2O3 on η-Al2O3 and SiO2 gel has been investigated using M?ssbauer spectroscopy and X-ray diffraction analysis. The results suggest that after appropriate treatment Eu2O3 disperses spontaneously onto the surface of both supporter materials. No indications of remaining crystalline Eu2O3 have been found below the limiting mono-layer concentration. In the case of η-Al2O3, it is suggested that below the limiting monolayer capacity Eu2O3 covers the surface in a disordered monolayer configuration. For higher Eu2O3 contents a second layer starts to appear with a structure similar to that of the bulk crystalline phase. In the case of SiO2 gel, it is suggested that the monolayer as well as the second layer configuration of Eu2O3 is highly disordered. It seems that the M?ssbauer parameters, isomer shift and linewidth allow additional insight into the surface layer structures formed by solid-solid adsorption.

The origin of iron complexes detected several years ago in the green stain on the bark of plane trees was not clear up to now. Using Mössbauer spectroscopy, we were able to show that these iron complexes result from air pollution deposits. Since all iron compounds detected in air pollution so far are also present in green stain on the bark of plane trees in high concentrations, it seems to be a very effective indicator of air pollution.

Fe-substituted Y-Ba-Cu superconducting oxide compounds were investigated by dc-magnetic susceptibility measurements, powder X-ray diffraction and Mdssbauer spectroscopy. Fe substitution caused a structural transformation from orthorhombic to tetragonal. Up to 4 at% Fe Tc was almost unaffected. It was found that superconductivity in Cu oxides does not depend on orthorhombic crystal symmetry.

The influence of Fe-substitution on the high-Tc superconductor YBa2Cu3O7 was studied by means of d.c.-magnetic susceptibility and X-ray powder diffraction. Fe was found to exist in the paramagnetic high-spin state. Superconductivity was found in the samples with up to 20% Fe. A 4% Fe-substitution induces a tetragonal structure at room temperature with almost no effect on Tc. The very high Tc of 89 K of this fully tetragonal phase indicates that the linear CuO chain might not be critical for the superconductivity.

AbstractThe dispersity of Eu2O3 on the surfaces of Al2O3 and SiO2 gel have been studied by Mössbauer spectroscopy and x‐ray diffraction analysis. The Mössbauer data allow some insight into the structure of the dispersed Eu2O3 for both carriers. X‐ray and Mössbauer data indicate that the surface adsorption of Eu2O3 on Al2O3 is different from that on SiO2.

The binary system LiNbO3-Fe2O3 has been studied by Mossbauer spectroscopy in the concentration range up to 24 mol% Fe2O3. For Fe2O3 concentrations up to 6 mol% iron is incorporated into the matrix of LiNbO3 as Fe2+ and Fe3+, whereby the Fe2+ content decreases with increasing Fe2O3 concentration. Samples containing 9 and 11 mol% Fe2O3 showed only the Fe3+ valence state. There were no indications of any considerable formation of superparamagnetic Fe2O3 clusters up to 11 mol% Fe2O3. This is in agreement with the X-ray and DTA investigations of Takei and Katsumata (1982) who found that a solid solution exists between 0 and 11 mol% Fe2O3. Above 11 mol% the appearance of magnetically split sextets in the Mossbauer spectra indicated the formation of a second α-Fe2O3 phase. The isomer shift, which reflects the electron density at the Fe nucleus, measured as a function of the Fe2O3 concentration showed two steps, one at 6 mol% Fe2O3 (the turning point of the CH axis parameter (Takei et al. 1982) and one a...

Amorphous LiNbO 3 doped with 0.22 at.% Fe 2 O 3 (90.7% enriched in 57 Fe) was prepared using the twin roller quenching technique. Mössbauer measurements indicate that the short range order structure is similar to that of the crystalline phase. Positron annihilation experiments revealed an increase of the positron lifetime in the amorphous phase which may result from an increase of free volume.

Mössbauer spectroscopy of Co germanides proves the existence of three stoichiometric phases: CoGe2, CoGe, and Co2Ge. The isomer shift values of these phases indicate covalent bonds between (Co)Fe and Ge. No magnetic ordering is observed down to 4.2 K. 57Co diffused in Ge results in a segregated phase, the Mössbauer parameters of which differ from the values of the stoichiometric compounds. The spectra of implanted samples indicate the existence of Co in a highly symmetric position (possibly tetrahedral) and at defect sites. Thermal annealing results in the same segregated phase as observed after Co diffusion. In Kobaltgermaniden können mößbauerspektroskopisch drei Phasen identifiziert werden: CoGe2, GoGe und Co2Ge. Die gemessenen Isomerieverschiebungen dieser Phasen lassen auf kovalente Bindungen zwischen (Co)Fe and Ge schließen. Bis zu Temperaturen von 4,2 K wird kein magnetischer Ordnungsvorgang beobachtet. Diffusion von 57Co in eine Ge-Matrix resultiert in einer Ausscheidungsphase, deren Mößbauerparameter von den Parametern der stöchiometrischen Zusammensetzung verschieden sind. Spektren von implantierten Proben zeigen Co auf hochsymmetrischen Gitterplätzen (möglicherweise Tetraeder) und auf niedersymmetrischen Defektplätzen. Nach Auslagerung der Proben entsteht dieselbe Ausscheidungsphase, wie sie nach der Eindiffusion von Co in Ge beobachtet wird.

Mössbauer spectroscopy of cobalt-silicides proved the existence of three stoichiometric phases: CoSi2, CoSi and Co2Si. The values of the hyperfine parameters indicated covalent bonds between Co and Si in all phases and could be understood on the basis of their crystallographic structure and of theoretical predictions for the electronic structure. For CoSi2, anomalous spectra were obtained, the origin of which was not clear. The different spectra of the cobalt-silicides permit the prospective use of Mössbauer spectroscopy for the study of formation and structure of Co/silicide/silicon interfaces.

The effect of fast magnetization reversal induced by external radio frequency (rf) fields has been studied in FeBO3 using the Mössbauer technique. The rf collapse and sideband effects were investigated as a function of intensity for two rf field frequencies: 62 and 36 MHz. The switching times estimated for magnetization reversal are of the same order of magnitude as in amorphous metals and Fe-Ni alloys. Because of the relatively short switching times the magnetization reversal must be of rotational character.

A study of Fe3+ environments in alkali silicate glasses has been performed. The Mössbauer parameters indicate Fe in octahedral as well as in tetrahedral surroundings. The broad linewidth of the Mössbauer subspectra indicates a distribution of the hyperfine parameters due to local distortions. Using a distribution fitting program we obtained information about the distortions of octahedral and tetrahedral Fe ion surroundings from the distribution of the electric field gradient (EFG).