Abstract: The electronic structure and magnetic properties of Ni/Al2O3/Ni tunnel junctions with O-terminated and Al-terminated interface models are investigated by first-principles discrete variational method with the local-spin-density approximation. The results show that the interface atomic has an important effect on interface electronic state and spin polarization as well as TMR ratio. For the O-terminated and Al-terminated interface models, spin polarization at Fermi level of Ni layers exhibit negative. It is found that absolute value of spin polarization as well as TMR ratio of Al-terminated interface models is much larger than that of O-terminated interface, which shows over-oxidization of Al layer could deteriorate magnetoresistance properties.

Abstract: First-principles calculations have been widely used to describe the ground state properties of materials over almost 20 years. Recently, a great progress was made in the first-principle calculations. Thermodynamic properties can also be gotten by calculations of the phonon densities of states (phonon DOS) and phonon dispersions of materials, which show widely potential applications in material researches. In the present work, the energetics and bonding properties of interfaces between ZrO2 and Ni metal were given by first-principles calculations. The results show that alloy element impurities (Al, Cr and Y) influence remarkably the adhesion of the ceramic and metal. On the other hand, the phonon densities of states and phonon dispersions of ZrO2 were calculated with density functional perturbation theory. From the phonon DOS, the thermodynamic properties were derived and the phase transformation of ZrO2 was discussed. By this method, the thermodynamic properties of material can be gotten from atom and electron levels without any experiment data. It is a new approach to design and study the thermodynamic properties in new material system.

Abstract: The electronic structures of anatase titanium oxides (TiO2) substitutional doping with N, F, C, P and S for O have been studied by first-principles method based on the density functional theory. The lattice distortion and densities of states of nonmetal-doped anatase TiO2 as well as photocatalytic activity were discussed. Comparing the effects of these five nonmetal ions (N, F, C, P and S) in the anatase TiO2, the substitutional doping of N is the most effective to get better visible-light activity because of its least lattice distortion and a large band-gap narrowing effect and the suitable relative position of the impurity states in band gap.

Abstract: The oxygen atom adsorption at Al-Al bridge, Ni-Ni bridge, Al top and Ni top site on the NiAl(110) surface by first-principles method within density functional theory has been studied in this paper. It has been found that the preferred adsorption position of the oxygen was at the Al-Al bridge site then the Ni-Ni bridge site. The charge transfer took place obviously between the O atom and the nearest Al atoms, but no charge transferred from the nearest Ni atoms to O atom. For the Al-Al (Ni-Ni) bridge adsorption site, the bond lengths of Al-O and Ni-O were about 1.741 Å (1.700Å) and 2.369Å (2.012Å), respectively, which means that the Al atom is easier to be oxidized than the Ni atom. It is revealed that the Al atom oxidized selectively and the chemical bond formed between the O ion and the nearest Al ions during the initial oxidation stage.

Abstract: Nb-Si-Cr alloys have shown great potential as the aviation materials because of their good mechanical properties and high temperature oxidation resistance. The thermodynamic properties of Nb, Cr₂Nb, α-Nb₅Si₃, β-Nb₅Si₃, as the main constituent phases of Nb-Si-Cr alloys, were calculated by first-principles methods combined with quasi-harmonic Debye model. The calculated results are in agreement with available experimental data. Compared the thermo-dynamic properties of different phases, it is found that the thermal expansions of these phases are similar and have the same trend with change of temperature. Thermal expansion coefficient of these phases are dependent with increases with temperature and decreases with pressure, respectively, while the bulk moduli decreases with increasing temperature. At last, the micro stress created by the differences in coefficients of thermal expansion between Nb and Cr₂Nb upon cooling was evaluated. The result showed that the stress is too small to cause cracking at the interface between Nb and Cr₂Nb.

Abstract: A series models of Ni3Fe/Al2O3/Ni3Fe magnetic tunnel junction with Al-terminated interfaces have been established for investigating the influence of ferromagnetic layer thickness on the electronic structure, employing first-principle methods based on local spin-density approximation theory. The spin polarization of the interfacial Ni3Fe monolayer shows a maximum value as the thickness of ferromagnetic layer increases. The Al monolayers at the ferromagnetic/insulating interface and the O monolayer in the interior of insulating layer are also studied in terms of the change of spin polarization with the ferromagnetic layer thickness. In addition, we have found that the structure of Ni3Fe monolayer has a great influence on the spin polarization.

Abstract: The structure and magnetic properties of fcc-Fe/Cu (100) superlattices have been investigated by the first-principles total energy calculation based on density functional theory (DFT). Through the optimization of the structure of Fe/Cu superlattices, it has been found that the interlayer spacing of Cu layers is contracted while the interlayer spacing of Fe layers is expanded. There are no obviously changes of Fe/Cu interfaces for Fe3Cu3 and Fe3Cu5 models. The layer spacing for Fe3Cu5 changes larger than that of Fe3Cu3 model, which results to a slightly larger magnetic moment of FeCu5 than that of Fe3Cu3 model. We also analyze the density of state near the Fermi surface and calculate spin asymmetry factor of each layer in Fe/Cu systems. Based on the two-current model, we evaluate the magnetoresistance ratio 21.8% for Fe3Cu3 and 22.8 % for Fe3Cu5 system.