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First principle calculations using supercell approach and coherent potential approximation (CPA) are performed to investigate the electronic and magnetic structures of Fe3-xMnxSi and Fe3-yMnySiy alloys, where x, y=0, 0.25, 0.50, 0.75, 1.00, 1.25, 1.5, 1.75, and 2.25. Using supercell calculations we obtained a metallic behavior for x=0, 0.25, and 0.5 in Fe3-xMnxSi alloys with spin polarizations of 24%, 39%, and 93%, respectively. The behavior starts to be half-metallic at x=0.75 with a small direct band gap that increases for higher concentrations of Mn. Among the half-metallic systems, only those of L21 structure at x=1 and 2 possess indirect band gaps along Γ-X symmetry line. The change of Si concentration in Fe3-yMnySiy structures retrieve the metallic behavior for all concentrations except y=1.25 that shows a half-metallic behavior with a direct band gap of 0.27 eV. We obtained a good agreement between supercell and CPA calculations for the values of the magnetic moment and the trends of the formation energies, which reveals the validity of the supercell approach in predicting the magnetic structure and the energetics of doped Heusler alloys. [ABSTRACT FROM AUTHOR]

Most of the engineering materials are alloys (solid solutions) and inevitably contain some impurities or defects such as vacancies. However, theoretical predictions of the hardness of this kind of materials have rarely been addressed in literature. In this paper, a hardness formula for multicomponent covalent solid solution is proposed based on the work of Sˇimunek and Vackárˇ [Phys. Rev. Lett. 96, 085501 (2006)]. With this formula, the composition dependence of the hardness is investigated for titanium nitrogencarbide (TiN1-xCx), off-stoichiometric transition-metal nitrides (TiN1-x and VN1-x), and B-doped semiconductors. The predicted hardness is in good agreement with experiments. To investigate the most frequently quoted correlation between hardness and elastic modulus, the elastic moduli of the systems involved in this paper have also been calculated. The results show that the elastic moduli cannot be used for rigorous predictions of the hardness of the solid solutions. [ABSTRACT FROM AUTHOR]

Ultrathin multiferroic BiFeO3 (BFO) films with self-assembled surface nano-islands on La0.67Sr0.33MnO3/(100) SrTiO3 substrates are fabricated by a one-step pulsed laser deposition process using the Bi-rich BFO target. It is revealed that these surface nano-islands mainly consist of conductive Bi2O3 outgrowths, which serve as top electrodes for the nanoscale BFO capacitor cells with lateral size of 10-30 nm. The ferroelectric BFO layer underneath these Bi2O3 nanoislands prefers certain complex domain structure with vertical and antiparallel polarization components (the so-called "anti-domain structure") and reduced domain switching fields. Moreover, these nanoscale capacitor cells exhibit the resistive switching IV behavior, offering opportunities for application in ultrahigh density non-volatile memories. [ABSTRACT FROM AUTHOR]

Martensitic transformation in Ni2+xMn1-xGa alloys is known to be controlled by the soft tetragonal elastic constant C′ of the high-temperature austenitic phase. The temperature (T) and composition (x) dependence of C′(T, x) are calculated using the first-principles exact muffin-tin orbitals method. We show that the temperature factor of C′ is dominated by the phonon-smearing term. The competition between the negative alloying effect (∂C′/∂x < 0) and the positive temperature effect (∂C′/∂T > 0) is found to lead to nearly constant C′(TM(x), x) at the critical temperature TM(x). We demonstrate that a proper account of the temperature and composition dependence of C′(T, x) is indispensable for reasonable theoretical TM(x) values. [ABSTRACT FROM AUTHOR]

The alloying effects of Nb, Zr, and/or Sn on the phase stability and elastic properties of Ti are investigated by using a first-principles method. Our calculation results indicate that a carefully designed Ti–Nb–Zr–Sn system can be a good candidate for low modulus biomedical materials. We find that the well-known correlation between the e/a ratio and both elastic and phase stabilities for Ti alloyed with transition metal elements breaks down for the Ti–Sn alloy. [ABSTRACT FROM AUTHOR]

A correction to the article "Hardness and elastic properties of covalent/ionic solid solutions from first-principles theory," published online in the August 2008 issue, is presented.