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Β2-ordered FeAl and Fe3Al composition amongst other various compounds of transition metals and aluminium compositions have been of significance to researchers for application in industries for steel-IT coating purposes due to their well-adherent protective oxide layer that forms on the surface of such alloys at the metal/gas interface. We employed Cluster expansion (CE) technique to predict meta-stable and stable compositions of Fe1-XPd/IrXAl ternary. A Cluster Expansion phase diagram was predicted, with five stable Fe1-XPdXAl structures and three stable Fe1-XIrXAl structures having the lowest formation energies, respectively. Employed a first-principles approach to predict the mechanical properties, with four and two Pd and Ir ternary doped ductile structures and DMol3 technique to determine temperature dependence dynamical properties, that is, the binding energy of Fe50Al50, FePdAl2 and FeIrAl2 at various temperatures. Our findings showed that doping on FeAl with Pd and Ir significantly enhanced the binding energy that more energy would be required to disassemble the particles of the Ir system into individual parts; the hardness and ductility of the material for high-temperature application component coating for steel-IT superior protection.

The measurement of the elastic constants of yttrium and aluminum garnet, in the temperature range of 300 to 1450K using a combination of Brillouin scattering and refractive index, enables the determination of associated quantities such as the bulk modulus, anisotropy ratio and thermo-optic coefficient. The Brillouin scattering includes laser light, incident on the compound of interest, which is scattered inelastically by thermal-acoustic phonons through elasto-optic coupling.

The measurement of acoustic mode frequency, lattice parameter and refractive index of simple crystals of cubic stabilized zirconia, in the temperature large range of 300 to 1450 Kelvin and using Brillouin scattering, X-ray diffraction and interferometric methods, enables the determination of elastic constants and associated quantities such as the bulk modulus, the anisotropy ratio and the Cauchy relation failure. A linear reduction in the elastic constants until the transition temperature T (sub C) is reached is dependent on the dopant concentration. The linear reduction effects are caused by the thermally generated disorder.

Graphical abstract Highlights • FePO 4 polymorphs are low in electrical conductivity due to wide band gaps. • The berlinite stabilizes at increased pressure above 4 GPa. • The phonon soft modes vanishes at transition pressure. • HP polymorph is thermodynamically stable as pressure increases. Abstract Olivine LiFePO 4 is a promising cathode material for lithium ion batteries. Its delithiated form FePO 4 has attracted interest as potential cathode for rechargeable lithium ion batteries due to high charge/discharge capacity and low cost. This paper report pressure dependence DFT + U calculations and stability of FePO 4 polymorphs. The heats of formation predict that berlinite polymorph is thermodynamically stable up to 4 GPa, while HP phase reaches a transition above 4 GPa at 0 K. The energy band gap is relatively wide, suggesting that FePO 4 polymorphs are low in electronic conductivity. However, conductivity is expected to improve at high pressure (4 to 7.5 GPa). All independent elastic constants are positive corresponding to stability of FePO 4 polymorphs, except for berlinite. Its phonon dispersion curves display negative vibrations along high symmetry direction (condition of instability) at 0 GPa. However, at pressure above 7 GPa, the berlinite becomes stable due to absence of soft modes. [ABSTRACT FROM AUTHOR]

Atomistic simulation techniques are used to investigate the surface structure, stability and reactivity of pyrite. Further, a potential model for FeS2, which reproduces experimental structural experimental structure parameters, elastic constants and hydration energies of pyrite is developed.

Abstract: In the current study, we report for the first time a new Ti rhombohedral (trigonal) structure induced by HEBM and subsequent sintering. During ball milling of Ti powder, solid-state transformation does not only depend on the grain refinement but also on the successful deformation of the nano-sized crystallites due to high energy ball impacts. Thermal stability of Ti-nanocrystalline in FCC allotrope was investigated. Upon sintering, the unstable FCC restored back to the rhombohedral phase rather than to HCP. The appearance of HCP Ti after sintering could suggest that prolonged milling leads to dispersion of hard particles (HCP) into more ductile particles belonging to allotropic phases, and hence possibility of resurfacing on sintering. [Copyright &y& Elsevier]

• Co20 wt.% Al powder was milled for 30 h. • A complete structural transformation was evidenced annealing at 600 °C. • Cubic spinel with a = 8.066 Å of ZnAl 2 O 4 prototype was formed. • A fibrous mesoporous morphology was developed on CoAl after annealing. Ball milling (BM) of elemental Co and Al was conducted for 30 h (h). This process has altered the original morphologies of both elemental Co and Al powders. Spherical Al powder particles has changed into a smooth pancake-shape while the original irregular-shaped Co agglomerates became disintegrated ultrafine particles. BM of the Co20 wt.% Al powder mixture after 30 h yielded thin irregular-shaped particles. XRD analysis revealed a partial structural transformation after BM and further structural change upon annealing the powder at 600 °C, as confirmed by the SEM images. The formation of the cubic spinel superstructure with lattice parameter a = 8.066 Å (ZnAl 2 O 4 prototype) and Fd-3 m # 227 space group was realized. By means of LEO 1525 field-emission scanning electron microscope (FE-SEM), a fibrous mesoporous structure was revealed on the milled powder after annealing the Co-Al mixture at 600 °C. The EDS analysis confirmed a minor N impurity on the annealed powder. [ABSTRACT FROM AUTHOR]

Abstract: We investigated the phase stability from B2 to L10/B19/B19′ in equiatomic PtTi alloy using the density functional theory within the generalized gradient approximation. Their structural, energetic, electronic and the mechanical properties were determined to show the stability trend of the shape memory binary alloy. The lattice parameters are well reproduced and agree to within 2% with the available experimental data. We found that the calculated heats of formation and density of states predicted B19 and B19′ PtTi to be the most stable structures compared to B2 and L10. On the other hand, their mechanical stability predictions show consistency with regard to the elastic constants and phonon dispersion curves. The elastic instability (negative C ij) and soft modes were observed in the B2, B19 and B19′ structures and not found in the L10 structure. [Copyright &y& Elsevier]

Abstract: Composition and temperature dependence of the crystal structure of IrTi with Ti content of 46–61 at.% was investigated using high-temperature X-ray diffraction analysis. Single-point energy calculations and geometry optimization were carried out based on first-principles calculations to understand the phase stability and transformation. Using X-ray diffraction analyses, a CsCl-type B2 structure was found in Ir-61 at.% Ti at room temperature; on the other hand, an orthorhombic structure in the alloys with Ti content below 58 at.%. The atomic positions obtained through first-principles calculations suggested a distorted L10 structure refined as a new orthorhombic (Cmmm #65) structure. The orthorhombic structure changed to almost a tetragonal structure with rising temperature and finally to a distorted B2 structure above 873 K in Ir-46–58Ti alloys. [Copyright &y& Elsevier]

Abstract: The deleterious low-temperature tetragonal phases in prototypical Pt-based superalloys have variously been reported as taking the tI16-U3Si (DOc), tI16-Ir3Si (DOc′) and tP16-Pt3Ga structure-types in contrast to the high-temperature cubic cP4-Cu3Au (L12) phase. We have investigated the relative stability of these four structure-types at absolute zero by using density functional theory. We find that the ground state of stoichiometric Pt3Al is tP16-Pt3Ga and that the other three lattices are mechanically unstable at absolute zero. Experiments are needed to measure the internal displacement parameters of these three competing tetragonal phases. [Copyright &y& Elsevier]