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The dependences of phonons on the spin structures of BaFe2As2 were studied using first-principles supercell approach. We considered the nonmagnetic, checkerboard, stripe, and spin-density-wave structures as well as a spin structure labeled as STR17. We find that STR17 is lower in energy than the stripe. It is seen the ∼20 meV missing peak at the generalized phonon density-of-states and the measured specific heat are well reproduced when the magnetic effects are accounted. We see phonon energy gaps for all the four magnetic structures but not for the nonmagnetic structure. [ABSTRACT FROM AUTHOR]

We have developed the means to grow BiMnO3 thin films with unparalleled structural perfection by reactive molecular-beam epitaxy and determined its band gap. Film growth occurs in an adsorption-controlled growth regime. Within this growth window bounded by oxygen pressure and substrate temperature at a fixed bismuth overpressure, single-phase films of the metastable perovskite BiMnO3 may be grown by epitaxial stabilization. X-ray diffraction reveals phase-pure and epitaxial films with ω rocking curve full width at half maximum values as narrow as 11 arc sec (0.003°). Optical absorption measurements reveal that BiMnO3 has a direct band gap of 1.1±0.1 eV. [ABSTRACT FROM AUTHOR]

Icosahedral short-range order, of which Al atoms are caged in the center of icosahedra with Cu and Zr atoms being the vertices, has been evidenced in the Cu46Zr46Al8 glassy structure by ab initio molecular dynamics simulation. These Al-centered clusters distribute irregularly in the three-dimensional space and form a “backbone” structure of the Cu46Zr46Al8 glass alloy. It is suggested that this kind of local structural feature is attributed to the requirement of efficient dense packing and the chemical affinity between Zr–Zr, Zr–Al, and Cu–Zr atoms. Our calculated results are found to be in good agreement with the experimental data. [ABSTRACT FROM AUTHOR]

This paper presents a computational evidence of icosahedral short and medium range ordering in Zr41Ti14Cu12.5Ni10Be22.5 bulk metallic glass using ab initio molecular dynamics simulation. It is found that 1551, 1541, and 1431 types of bond pairs are pronounced in both the liquid and glass states, resulting in icosahedral coordinate polyhedra at low temperatures. By linking the individual icosahedra through vertex-, edge-, face-, and intercross-shared atoms, icosahedral medium range ordering is formed. The predicted homogenized structure factor and pair correlation function of the glass structure have been confirmed to be in agreement with the experimental results. [ABSTRACT FROM AUTHOR]

BiFeO3 thin films have been deposited on (001) SrTiO3 substrates by adsorption-controlled reactive molecular-beam epitaxy. For a given bismuth overpressure and oxygen activity, single-phase BiFeO3 films can be grown over a range of deposition temperatures in accordance with thermodynamic calculations. Four-circle x-ray diffraction reveals phase-pure, epitaxial films with ω rocking curve full width at half maximum values as narrow as 29 arc sec (0.008°). Multiple-angle spectroscopic ellipsometry reveals a direct optical band gap at 2.74 eV for stoichiometric as well as 5% bismuth-deficient single-phase BiFeO3 films. [ABSTRACT FROM AUTHOR]

First-principles calculations are performed on MgB2, carbon doped MgB2, and MgB2C2. The trend of calculated lattice parameters of MgB2 with increasing carbon content agrees with bulk experiments but not with thin films produced by hybrid physical-chemical vapor deposition. In this work, the authors propose a model to explain this behavior based on the coefficients of thermal expansion of MgB2 and MgB2C2 as predicted from first principles and of graphite from literature. It is concluded that the effect of carbon on the lattice parameters of MgB2 thin films is extrinsic and due to differences of the coefficients of thermal expansion of different phases. [ABSTRACT FROM AUTHOR]

Focuses on the attraction of layered cobaltate NaxCoO2 due to its exceptional properties. Attribution of layered cobaltate NaxCoO2 to the spin entropy due to the strong electron correlation effects; Description of the structural and transport properties of epitaxial thin films.

The dependences of phonons on the spin structures of BaFe2As2 were studied using first-principles supercell approach. We considered the nonmagnetic, checkerboard, stripe, and spin-density-wave structures as well as a spin structure labeled as STR17. We find that STR17 is lower in energy than the stripe. It is seen the ∼20 meV missing peak at the generalized phonon density-of-states and the measured specific heat are well reproduced when the magnetic effects are accounted. We see phonon energy gaps for all the four magnetic structures but not for the nonmagnetic structure. [ABSTRACT FROM AUTHOR]