Zoltán Dankházi

Electronic distributions of states in crystalline and quasicrystalline Al-Cu-Fe and Al-Cu-Fe-Cr alloys

Valence and conduction state distributions in a series of Al-Cu-Fe and Al-Cu-Fe-Cr alloys of different structural states and nominal compositions have been investigated by means of soft X-ray emission and photoabsorption spectroscopies. A complete description of the valence band is obtained. The DOS at EF is observed to be very low which is consistent with the high resistivity values found for the icosahedral quasicrystalline phase. The existence of a wide pseudo-gap at EF is evidenced, which is higher in the quasicrystal than in be related crystalline counterparts.

Electronic structure of Al-Pd-Mn crystalline and quasicrystalline alloys

An experimental and theoretical analysis of the electronic structure of Al-Pd alloys is presented. The experimental study, based on soft x-ray emission and absorption spectroscopies, is further extended to the case of quasicrystalline Al-Pd-Mn alloys and their approximants. The electronic structure is dominated by the sp-d hybridization. The Al-sp band is strongly modified by the interaction with the Pd-d states in the middle of the valence band. Close to the Fermi level, hybridization with the Mn-d states is found to enhance the structure induced pseudo-gap in the Al partial density of states, both in the icosahedral and the decagonal quasicrystalline phases.

Theoretical and experimental investigation of the electronic structure of Ti-Zr-Ni and Ti-Zr-Ni:H alloys

Abstract We have calculated the band structure of a model 1/1 approximant of cubic Frank-Kasper type structure of the icosahedral Ti–Zr–Ni quasicrystal. We have shown that the electronic structure is dominated by the metals d bands with a complete mixing of Ti and Zr states. With respect to the pure metal, Ni d states appear to be strongly modified upon alloying. The experimental investigation of the icosahedral alloy shows good agreement with the theoretical calculations for the approximant. We have shown experimentally that dramatic modifications of both occupied and unoccupied states occur in the hydrogenated quasicrystal, due to bonding to H. We have asserted preferential Zr–H rather than Ni–H bonding. We have suggested that Ti–H bonding should also be significant. We interpret the high H/metal ratio by the fact that H bonds to each of the elements in the quasicrystal.

Al p Conduction States in Quasi-Crystalline Al-Cu-Fe Alloy and Related Compounds

We have examined in details the Al p conduction states as well as the Al 3p valence distributions in quasi-crystalline Al62Cu25.5Fe12.5, rhombohedral approximant R-Al62.5Cu26.5Fe11 and tetragonal ω-Al7Cu2Fe phase. A significant issue is that, in a wide energy range beyond the Fermi level, there is a noticeable decrease of the density of the Al p conduction states in the quasi-crystalline material. Conversely, the conduction Al p band is very much different in metallic aluminium, whereas the situation is found intermediate in the ω- and R-compounds. We point out that a major difference between the icosahedral quasi-crystalline alloy and its rhombohedral approximant is shown by the conduction electronic distributions in contrast with many other properties which, as is well known, present no significant difference. Such a behaviour may be ascribed in part to the progressive disappearance of the crystalline periodic order. Our result is the first experimental evidence in favour of theoretical predictions made elsewhere that the electronic band structure of approximant phase and merely of quasi-crystals consists in a succession of numerous spikes and gaps.

Evidence of a wide pseudo-gap in AlCuFe icosahedral alloys☆

Using X-ray spectroscopy experiments electronic distributions of both valence and conduction bands have been investigated separately in icosahedral Al63Cu25Fe12 and crystalline ω-Al7Cu2Fe. Photoemission measurements determine the position of the Fermi level; this allows comparison of the various electronic distributions. Effects of hybridization are found. Both a quite low Al density of states at the Fermi level and a rather wide pseudo-gap are observed in the icosahedral phase; such a pseudo-gap also exists in the crystalline alloy but it is smaller by a factor three. Besides hybridization effects, a possible charge transfer to Fe orbitals is proposed to interpret the empty Fe d electronic distributions of the alloys.

On the metastable states of amorphous Fe84-xWxB16 (0 ≤ x ≤5) alloys

Abstract A stability investigation of Fe 84− x W x B 16 alloys is given for the interdependence of thermal properties of crystallization and changes in the electronic structure. For the thermal analysis and for electronic structure, DTA and SXS methods were used, respectively. A systematic interaction of the electronic structure and the heat of crystallization was observed. Based on this data, the role of the electronic structure in the stability is determined. General remarks on stability are given from the trends of measured data.

Comparison of theoretical and experimental electronic distributions of Si - Ni and Si - Er alloys

The total and partial densities of states of , and have been calculated using a scalar relativistic self-consistent augmented plane-wave method () or a self-consistent linear muffin-tin orbital method in the atomic sphere approximation ( and ). The x-ray photoemission valence band and soft-x-ray emission Si K and Ni L spectra have been calculated by applying appropriate broadening factors to the theoretical densities-of-states curves; in the case of the x-ray photoemission spectra, photoionization cross sections have been taken into account. Very good agreement is found between the experimental x-ray photoemission and soft-x-ray emission spectra and the simulated spectral curves.

Interdependence of the thermal properties and electronic structure of Y1Ba2CuxOy, (1.5≤x≤9) ceramics

A definite correlation between the thermal and electronic properties of Y1Ba2CuxOy perovskite materials has been observed using differential thermal analysis (DTA) and X-ray fluorescence spectroscopy (XFS). The compound Y1Ba2Cu3O7−z shows anomalous transition enthalpy and copper-oxygen hybridization with respect to other compounds with different copper content.

EBSD Sample Preparation: High Energy Ar Ion Milling

Surface quality development on series of metal samples was investigated using a new Ar ion milling apparatus. The surface quality of samples was characterized by the image quality (IQ) parameter of the electron backscatter diffraction (EBSD) measurement. Ar ion polishing recipes have provided to prepare a surface appropriate for high quality EBSD mapping. The initial surfaces of samples were roughly grinded and polished. High quality surface smoothness could be achieved during the subsequent Ar ion polishing treatment. The optimal angles of Ar ion incidence and the polishing times were determined for several materials.

Effect of High Energy Ar-Ion Milling on Surface of Quenched Low-Carbon Low-Alloyed Steel

Surface preparation for electron backscatter diffraction (EBSD) measurements requires a lot of time and experience. We chose a lath martensitic iron based alloy to demonstrate the efficiency of ion polishing techniques. The average image quality (IQ) values from the EBSD measurements were assigned to be the characteristic parameter for surface goodness. The ideal ion sputtering time and the angle of incidence were determined, and the corresponding inverse pole figure (IPF) and IQ maps were compared to the mechanical polishing treatment.