Papers by Keyword: Electronic Structure

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Authors: Sergey Dunaevsky, Evgeny Mikhailenko
Abstract: The results of "ab-initio" calculations of spin - polarized electronic structure, total energy and the local atomic magnetic moments of some manganite surfaces are presented. A slab consisting of one, three, five or, in some cases, seven layers of Mn-O atoms. is used to model the CaMnO3 (CMO), LaMnO3 (LMO) (001) surface. Total energies calculations of magnetic properties of manganites surfaces were performed using density-functional theory (DFT) and the pseudopotential method. We have found that on the surface layers without structural optimization manganese atomic magnetic moment is higher than in the bulk and “dead layers”, where all the local moments are zero, have not been found. All the above ultrathin films appeared ferromagnetic semimetals with almost complete polarization of DOS near the Fermi level.
Authors: Jing Wen, Chun Ying Zuo, Cheng Zhong
Abstract: Motivated by the widely discussed Ag doped ZnO and the lack of follow-up reports about the realization of p-n junctions, we calculated the electronic structures and optical properties of pure, Ag-doped and Ag-F codoped ZnO based on the density-functional theory. It was found that Ag doped ZnO shows p-type conduction character. But there are some unstable factors and self-compensations in this structure. We also calcualted the formation energy and ionization energy of the impurity for Ag-F codoped ZnO. It was found that incorporating the reactive donor F into Ag doped ZnO system, not only enhances the Ag acceptor solubility, but also gets a shallower Ag acceptor energy level in the band gap. In addition, we analyze the imaginary part of the dielectric function, reflectivity and absorption coefficient for pure ZnO and Ag-F codoped ZnO. Compared with the pure ZnO, the remarkable feature for Ag-F codoped ZnO is that there is a strong absorption in the visible-light region, which indicates that it could be taken as a potential candidate for a photocatalytic material.
Authors: Xin Tan, Yu Qing Li, Xue Jie Liu
Abstract: With a motivation to understand microscopic aspects of TiN relevant to the electronic structure, phonon and thermal properties of transition metal nitride TiN superlattices, we determine its electronic structure, phonon spectra and thermal properties using first-principles calculations based on density functional theory with a generalized gradient approximation of the exchange correlation energy. We find that the electronic bands crossed by EF are half occupied, TiN has the ability of taking part in chemical reactions and also has the surface activity; A large gap in its phonon spectra, anomalies in the phonon dispersion of metallic TiN, manifested as dips in acoustic branches, but it do not contain soft modes in any direction; The specific heat (Cv) of TiN rises rapidly at low temperatures, the Cv values of the material, is identical to the Dulong-Petit value at high temperatures. Under the quasi-harmonic approximation (QHA), the thermal expansion, specific heat and bulk modulus B(T) are obtained, and the B(T) decreases along with the increase of temperature.
Authors: Yu Wang, Hong Li, Ying Guo Yang, Geng Wu Ji, Kong Chao Shen, Hao Liang Sun, Jiong Li, Zheng Jiang, Fei Song
Abstract: The beta-phase of Zn4Sb3 has been regarded as a very promising thermoelectric material since middle nineties, owing to its unique merit: intermediate temperature region (200-400 °C), made of cheap, non-toxic and abundant elements and high thermoelectric property. However, the thermal stability of Zn4Sb3 seems to be an inherent obstacle for the practical application during the working temperatures. Herein, magnesium doped Zn-Sb semiconductor (Mg0.04Zn3.96Sb3) was investigated thoroughly in-situ during thermal annealing up to 600 K, whilst both microstructure and electronic structures were recorded via the combination of synchrotron-based two dimensional X-ray diffraction techniques and the X-ray photoemission spectroscopy. While the time-resolved grazing incidence XRD reveals the preserved crystal structures during thermal annealing to 600 K, XPS measurement demonstrate the robustness of electronic structures. On basis of these findings, it was concluded in the end that the doping of magnesium significantly improves the thermal stability of zinc-antimonite compounds and introduces minor influence on the electronic structure of Zn-Sb alloy. Our study may propose an effective approach towards the wild application of Zn4Sb3 related thermoelectric materials.
Authors: G. Ahmed, B.L. Ahuja, N.L. Heda, Vinit Sharma, A. Rathor, B.K. Sharma, M. Itou, Y. Sakurai, Soma Banik
Abstract: We present the first ever theoretical and experimental charge Compton profiles of Ni2MnGa Heusler alloy. The measurements have been made using magnetic Compton spectrometer at SPring8, Japan. The Compton profiles and energy bands have been computed using Hartree-Fock, density functional theory with local density and generalized gradient approximations. It is seen that the Hartree-Fock based Compton profile is relatively in better agreement with the experimental profiles. In addition, we also report the energy bands, density of states and valence charge densities using full potential linearized augmented plane-wave method.
Authors: F.Z. Boujrhal, El Kebir Hlil, R.Cherkaoui El Moursli, T. El Khoukhi, B. Sghir
Abstract: Comparative radon investigations of two natural materials, crystalline apatite and amorphous oxide, are presented here. The radon retention in the apatite (sedimentary apatite) is more than 70% of the total radon formed in the solid matrix. The amorphous oxide (gel hydrothermal alteration) retains only 7% of radon. The nature of the material which plays an important role in the radon diffusion is confirmed by heat treatment. The major and interesting result of this heat treatment is increasing of crystallite size. This phenomenon induces improvement on radon retention ability. To study these properties one uses a structure band calculations based on the Linear Combinations of Orbital Atomic (LCAO) method convenient numerically for the ionic systems.
Authors: Irina A. Shikhman, Marina G. Shelyapina, Galina S. Kupriyanova
Abstract: Magnetite is a very promising candidate for hard electrode in magnetic tunnel junction devices due to its electronic and magnetic properties. Addition of a buffer iron layer improves required properties. Here we report on the results of our DFT study of the impact of the additional Fe buffer layer on the electronic and magnetic properties of magnetite.
Authors: D.M. Hunter, R.I. Grynszpan
Authors: Hong Li Wu, Xin Qing Zhao, Jian Xu, Chun Gen Zhou, Hui Bin Xu
Abstract: A first principle study was performed to discuss the high temperature oxidation mechanism of NiTi alloys with the special emphasis on the effect of Nb on the oxidation behavior. The calculation results suggest that the Nb atom prefers the Ti site in Ni(Ti,Nb). The addition of Nb will not only reduces the electron density of Ti-d and Ni-d states near the Fermi energy level but the their electron contributions to the p-orbital of Ti. In addition, the Nb atom increases the formation energy of the Ti defect, which will decrease the diffusion of Ti atoms. All these Nb-induced effects account for the improvement of high temperature oxidation resistance, which agrees well with the experimental results.
Authors: Hiroyuki Kawanishi, Yoshinori Hayafuji
Abstract: It is known that acceptor-carbon complexes have ionization energies less than those of the corresponding substitutional, separate acceptors in silicon. We present the formation mechanism for a shallower acceptor energy level called an X level that is due to an indium- carbon pair. Ab initio calculation methods were used to evaluate electronic structures and lattice relaxations of silicon with indium, carbon or a carbon-indium dimer. The results shows that the bonding interaction between the 5p orbitals of the indium atom and the 3sp orbitals of the silicon atoms bound with the indium atom mainly determines the ionization energy of the X level, and the ionic bonding interaction of the carbon atomic orbitals with the indium atomic orbitals in the X level enables the bonding interaction of the orbitals between the indium atom and the silicon atom to lower the corresponding indium acceptor level, and then to form the shallower X level.
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