F Vanderwoude

A CELLULAR ATOMIC MODEL FOR THE MOSSBAUER ISOMER-SHIFT OF AU-197 IN ALLOYS

Abstract It is demonstrated that the atomic model previously shown to give a semi-quantitative account of the heat of formation of transition metal intermetallic compounds, can also offer a relatively simple interpretation of the isomer shift in metallic alloys. The two main terms in the isomer shift are due to (1) electronic charge transfer between more electropositive and more electronegative metal atoms and (2) the discontinuity in the electron density that exists at the boundary between disimilar atoms if the atoms have similar charge distributions in both alloy and the pure metals. The electron density must become continuous at the cell boundary; this leads to a term in the isomer shift that usually, but not always, opposes the charge transfer term. In solid solutions there is an additional volume (size mismatch) contribution to the isomer shift which, however, is not as important as suggested by some other authors. In addition to experimental results obtained on the isomer shift of solid solutions of Au as an impurity in transition metals hosts, we discuss results on Au-base alloys and gold intermetallic compounds.

EFFECT OF MN ON THE MAGNETIC-MOMENTS OF FE IN INTERMETALLIC COMPOUNDS

Abstract Mossbauer and magnetic measurements are reported on the ferromagnetic (Fe 1- x Mn x ) 2 Y and (Fe 1- x Mn x ) 2 B intermetallic compounds. Assuming proportionality between the iron hyperfine field and iron magnetic it is found that the manganese is nonmagnetic in these systems.

Crystallization kinetics of iron-boron metallic glasses

The crystallization of Fe1−xBx glasses were investigated in the 12 < x < 26 concentration range by Mossbauer spectroscopy and differential scanning calorimetry. The kinetics of α-Fe formation was determined from in-situ Mossbauer spectroscopy while the total crystalline fraction is estimated by measuring the remaining energy of crystallization after several isothermal heat treatments of different duration. In order to support our conclusion the decomposition kinetics of the crystalline Fe3B intermetallic compound to α-Fe and Fe2B were also investigated. The exponents characteristic of the kinetic processes in the crystallization and decomposition transformation are determined. The formation of α-Fe is shown to be long range diffusion controlled over the whole composition region while the crystallization of Fe3B is interface limited. Our results indicate the presence of two separate processes and cannot be explained on the basis of a eutectic mechanism in any composition ranges.

STRUCTURAL ORDER AND HOMOGENEITY IN NI3AL

Abstract The process of ordering in mechanically disordered Ni3Al has been followed by means of X-ray, susceptibility and Mossbauer measurements. A short anneal at 800° is sufficient to restore the long range order completely. An anneal of at least ten days appears to be necessary for achieving homogeneity.

XPS-STUDY OF FE (4-5A/O) X-ALLOYS WITH X=AL, SI, GA, GE, AS, SN, SB

Abstract An XPS-study of Fe (4−5 a/o) X-alloys, X = Al , Si , Ga , Ge , As , Sn , and Sb , is reported. The binding energy shifts in FeX are −0.9 eV and −0.6 eV for Al and Ga, respectively, −0.3 eV for As and Sb and zero for Si, Ge, Sn and Fe. The shifts for Al and Ga are interpreted as a volume effect. No difference was found between the valence bands of the dilute alloys and pure Fe.

ANOMALIES IN TEMPERATURE-DEPENDENCE OF HYPERFINE FIELDS IN SN DOPED AND PURE MAGNETITE

Abstract A Mossbauer study of the behavior of the hyperfine interactions at the 57Fe and 119Sn nuclei in Fe3O4 and Sn doped Fe3O4 has revealed anomalies in the temperature dependence of these hyperfine fields in the Verwey transition temperature region.

SOME ASPECTS OF A STUDY OF DILUTE FEX ALLOYS, WITH X NON-TRANSITION ELEMENTS AL, SI, GA, GE, AS, SN AND SB

Abstract By temperature dependent Mossbauer measurements the magnetic hyperfine fields at different iron sites are determined. The Curie temperatures are also determined. These results are interpreted in terms of a modified Zener-Vonsovskii model.