I. Dézsi

Mössbauer‐effect study of Co57 and Fe57 impurities in ferroelectric LiNbO3

The Mossbauer effect observed with LiNbO3:Co57 (source) and LiNbO3:Fe57 (absorber) crystals showed the existence of high‐spin Fe2+ and Fe3+ valence states. The Fe2+/Fe3+ ratio could be changed by reducing or oxidizing heat treatment. Fe3+ in sources and absorbers shows Mossbauer spectra which are typical for slow electronic relaxation between the crystal field states of the 6S5/2 state ion. For both Fe3+ and Fe2+, the principal axis of the electric field gradient is found to be parallel to the crystallographic c axis. For ferric iron Vzz is positive, while Vzz is negative and strongly temperature dependent for ferrous iron. The impurity site substitution and charge compensation mechanism are discussed.

Temperature dependence of the electric quadrupole splitting in Fe(ClO4)2·6H2O

Abstract The value of the quadrupole splitting in Fe(ClO4)2·6H2O ferrous salt studied by Mossbauer effect was found to drop from 3.0 mm/sec to 1.5 mm/sec in a temperature interval of ± 15°C around -36°C while both pairs of lines could be observed within the 30° transition temperature interval.

Phase transition in nanomagnetite

Recently, the application of nanosized magnetite particles became an area of growing interest for their potential practical applications. Nanosized magnetite samples of 36 and 9nm sizes were synthesized. Special care was taken on the right stoichiometry of the magnetite particles. Mossbauer spectroscopy measurements were made in 4.2–300K temperature range. The temperature dependence of the intensities of the spectral components indicated size dependent transition taking place in a broad temperature range. For nanosized samples, the hyperfine interaction values and their relative intensities changed above the Verwey transition temperature value of bulk megnetite. The continuous transition indicated the formation of dendritelike granular assemblies formed during the preparation of the samples.

Mössbauer study of bridged ferrocene derivatives

Abstract The molecular geometry of a series of trimethylene bridged ferrocene derivatives has been studied by means of Mossbauer techniques. The differences in quadrupole splitting and isomer shift among the various derivatives can best be explained as being due to differences in the planarity of the cyclopentadienyl rings.

XPS investigations of FeSi, FeSi2 and Fe implanted in Si and Ge

Polycrystalline FeSi and FeSi2 samples have been examined by ESCA experiments. The valence band spectra show features that can be attributed to bonding and non-bonding states, as is the case for other transition metal silicides, where bonding is expressed in terms of hybridisation. Furthermore the authors have investigated the photoelectron spectra of samples of Si and Ge implanted with Fe at an energy of 40 keV in order to draw some conclusions regarding the character of the Fe-Si bonding in the disordered layer. The concentration of Fe as a function of the sample depth was also determined and compared with the results of Monte Carlo calculations.

Measurement of the g-factor of the 412 keV state in Hg198

The precession in the internal field of the angular correlation pattern of the 675 kev--412 kev cascade of Hg/sup 198/ following BETA -decay of Au/sup 198/ was measured to determine the g-factor of the 412-kev state. g was found to be +0.38 plus or minus 0.68. (R.E.U.)

A study of amorphous Fe79B21 alloy powders produced by chemical reduction

Abstract Ultrafine amorphous Fe 79 B 21 alloy powders have been successfully produced by chemical reduction. These powders consist of particles of nearly spherical shape with diameters between 100 and 500 nm. A comparison between as-prepared amorphous Fe 79 B 21 powders and Fe 80 B 20 ribbons prepared by melt-spinning is presented. The crystallization behaviour of the Fe 79 B 21 amorphous alloy powders has also been investigated by Mossbauer spectroscopy. A different crystallization behaviour compared with that of amorphous Fe 80 B 20 ribbons has been observed. In the case of Fe 80 B 20 amorphous alloy ribbons produced by the melt-spinning technique, eutectic crystallization is commonly observed resulting in two crystalline phases: α-Fe and Fe 3 B. This kind of crystallization was not observed in the chemically prepared samples. After annealing, the amorphous powder samples entirely crystallized into three crystalline phases: α-Fe, Fe 3 B, and Fe 2 B. The metastable tetragonal Fe 3 B phase transformed completely into α-Fe and Fe 2 B after annealing at 973 K for 1 h.

Cobalt-silicide structures studied by Mössbauer spectroscopy

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 phase transition in Fe(ClO4)2·6H2O

Abstract The Mossbauer spectrum of Fe(ClO 4 ) 2 ·6H 2 O is studied as a function of temperature and applied magnetic field. The electric quadrupole interaction changes its sign and magnitude by a factor 2 at 258 K on heating and at 243 K on cooling.

On the preparation of 57Co Mössbauer sources

Abstract A method developed for the preparation of 57Co sources appropriate for Mossbauer effect measurements is described. Investigations have been performed to establish the 57Co electrodeposition rate on stainless steel, Cu, Fe and Pd surfaces. The efficiency of the electrodeposition to adequately pretreated surfaces was found to be better than 90%. The total 57Co activity deposited on the surface can be diffused into the metal. The width of the 14.4 MeV gamma line emitted from the source does not exceed the theoretical value by more than 50%. Using a stainless steel absorber of 21 mg/cm2 thickness, the intensity of the effect is found to be 50%.