Magnetic origin of the chemical balance in alloyed Fe-Cr stainless steels: First-principles and Ising model study

Iron-chromium is the base material for most of the stainless steel grades. Recently, new insights into the origins of fundamental physical and chemical characteristics of Fe-Cr based alloys have been achieved. Some of the new results are quite unexpected and call for further investigations. The present study focuses on the magnetic contribution in the atomic driving forces related to the chemical composition in Fe-Cr when alloyed with Al, Ti, V, Mn, Co, Ni, and Mo. Using the ab initio exact muffin-tin orbitals method combined with an Ising-type spin model, we demonstrate that the magnetic moment of the solute atoms with the induced changes in the magnetic moments of the host atoms form the main factor in determining the mixing energy and chemical potentials of low-Cr Fe-Cr based alloys. The results obtained in the present work are related to the designing and tuning of the microstructure and corrosion protection of low-Cr steels. (C) 2014 Elsevier B. V. All rights reserved.</p

Electronic and structural analysis of Sb-induced GaAs(100)(2x4) and (2x8) surfaces

Electronic and structural properties of Sb-induced GaAs(100)(2x4) and (2x8) surfaces are studied by means of core-level and valence-band photoelectron spectroscopy utilizing synchrotron radiation and scanning tunneling microscopy. Combining these results and showing good consistency among them, we demonstrate that the Sb/GaAs(100)(2x4) surface is well compatible with the delta structural model, which includes one Sb dimer in both the first and third atomic layers and two second-layer Ga dimers per unit cell (i.e., the Sb coverage of 0.5 ML), giving experimental support to generality of the delta-type model for III-V(100)(2x4) surfaces, proposed previously on the basis of ab-initio calculations. Deconvolution of the Sb 4d core-level spectrum from the (2x4) surface shows two components, which are tentatively connected to two inequivalent Sb-dimer sites in the delta unit cell. Angle-resolved valence-band photoelectron spectroscopy reveals Sb-induced surface-derived states at near 0.4 and 0.6 eV below the valence-band maximum (VBM) for the Sb/GaAs(100)(2x4) surface, which have not been found in earlier measurements. These two surface-derived features mapped along symmetry lines of the surface Brillouin zone are identified with previous electronic-structure calculations. The results are also compared to band-structure measurements of the As/GaAs(100)(2x4) surface found in the literature. For the Sb/GaAs(100)(2x8) surface, we propose a structural model which, in contrast to the recent model, obeys the electron counting rule and consists of Sb dimers in three atomic layers, showing the Sb coverage of 1.25 ML for the (2x8) surface. The Sb 4d core-level spectrum from this surface exhibits three components, which are discussed within the determined structural model. The valence-band measurements of the (2x8) surface propose a new Sb-induced surface state at near 0.5 eV below the VBM

Electronic and structural properties of GaAs(100)(2x4) and InAs(100)(2x4) surfaces studied by core-level photoemission and scanning tunneling microscopy

Electronic and structural properties of GaAs(100)(2x4), InAs(100)(2x4), and Sb/InAs(100)(2x4) reconstructed surfaces have been studied by synchrotron-radiation photoelectron spectroscopy and scanning tunneling microscopy (STM). Based on the difference spectrum of As 3d core-level spectra of III-As(100)(2x4), measured in different surface-sensitivity conditions, as well as the line shape of the As 3d emission from the Sb-induced (2x4) surface, we give evidence that the As 3d spectra of GaAs(100)(2x4) and InAs(100)(2x4) consist of two surface-core-level-shifted components. One of them is shifted about 0.2 eV to the lower kinetic energy from the bulk component. On the basis of the relative component intensities, this surface-shifted As 3d component is assigned to the emission from the first-layer As dimers in the established model of the (2x4) surface. The other component, shifted about 0.3 eV to the higher kinetic energy, is connected to the third-layer As-dimer site. The comparison of the core-level results between GaAs(100)(2x4) and InAs(100)(2x4) suggests that the alpha 2 phase, which has one As dimer in both the first and third atomic layers per unit cell, exists on GaAs(100)(2x4), similarly to the case of InAs(100)(2x4), as predicted in theory but not observed to date. Furthermore, the STM observation of the GaAs(100)(2x4)alpha 2 phase is reported