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Abstract: Influence of temperature on the elastic properties of Mg2X (X=Si, Ge, Sn, and Pb) compounds, has been studied using first-principles calculations, within the generalized gradient approximation, and compared with the available experimental data in the literature. Elastic stiffness coefficients calculated with respect to volume (c ij (V)) have been correlated to the equilibrium volume as a function of temperature V(T) from phonon calculations to obtain temperature dependence of elastic stiffness coefficients c ij (T). A good agreement between the thus predicted elastic constants and experimental data has been achieved. The general trend in the bulk modulus (B), shear modulus (G) and Young''s modulus (E) seen for the compounds is Mg2Ge>Mg2Si>Mg2Sn>Mg2Pb. Elastic anisotropy, fracture toughness and stiffness of the compounds have been analyzed as a function of temperature based on their anisotropic ratio (2c 44/(c 11–c 12)), product of bulk modulus and volume (B × V 1/3), and Young''s modulus. The results obtained herein provide a better understanding of the elastic behavior of antifluorite compounds as a function of temperature. The methodology used in this work acts as a benchmark for future first-principles work that involves calculating elastic constants as a function of temperature. [Copyright &y& Elsevier]

First-principles results for the full set of elastic constants (stiffnesses) c ij of cementite, Fe3C, revealed an extreme elastic anisotropy with a very small c 44 amounting to only about 1/10 of c 55 and c 66. Synchrotron X-ray diffraction stress measurements were performed on Fe3C layers grown on α-Fe exhibiting a planar state of compressive residual stress. These data exhibit a characteristic hkl-dependence of the stress-induced reflection shifts, and provide experimental proof for the extreme elastic anisotropy of Fe3C. [Copyright &y& Elsevier]

Abstract: By using the first-principles projector-augmented wave method, the phase stability together with the bulk modulus and magnetic moment have been investigated in binary and ternary interstitial phases ε-Fe6C x , ε-Fe6N y and ε-Fe6C x N y (x, y =0,1,2,3 and x + y ⩽3) with a hexagonal structure. The predicted bulk modulus and volume of the ε phases increase with increasing the interstitial content, while the calculated magnetic moment decreases. The present work indicates that the longer the distance between the interstitial atoms, the lower the energy of the ε phases, i.e. the interaction between the interstitial atoms is of repulsive nature. The presently predicted phase stability of the ε-Fe6C x N y phases provides helpful insights into understanding the processes occurring during carbonitriding in steel and the further development of magnetic (carbo)nitrides. [Copyright &y& Elsevier]

Abstract: SeaWiFS chlorophyll and AVHRR SST time series as well as in situ measurements in August 1998 were used to evaluate short-term variability of chlorophyll associated with upwelling events in the western Taiwan Strait. The extent of eutrophic waters (SeaWiFS ), colder upwelling waters, and upwelling index were calculated for the western strait and for the northern and southern portions. Large extents of eutrophic waters were always accompanied by colder upwelling waters, indicative of the tight coupling of chlorophyll with upwelling activities. The phytoplankton growth lagged the upwelling activities by about 2 days. The temporal changes of upwelling events were found different in the northern and southern Taiwan Strait. A short relaxation of upwelling probably occurred between early and mid-August in the northern portion. One strong upwelling event likely lasted from early through mid-August, peaking before August 13 in the southern portion. It resulted in chlorophyll enhancement but with different timing of chlorophyll reaching maximum values in these two upwelling zones. The duration of one upwelling event in the western Taiwan Strait in August was estimated to be about 12 days. It seems that two distinctive northern and southern upwelling systems in the western Taiwan Strait were connected with, and affected by, the East China Sea and the South China Sea, respectively. [Copyright &y& Elsevier]

Abstract: The atomic structure and diffusivity in liquid Al80Ni20 are studied by ab initio molecular dynamics simulations. The local structures are analyzed by the pair correlation function, structure factor, coordinate number, Honneycutt–Anderson bond pair, and Voronoi tessellation methods. It is observed that the amount of icosahedral clusters increases, and the liquid becomes more ordered as the temperature decreases. The predicted self-diffusion coefficients of Al and Ni via the mean square displacements are very close to each other and agree well with the quasi-elastic neutron scattering measurements in the literature. The observation of equal self-diffusivity of Al and Ni is attributed to the formation of local solute-centered polyhedra, coupling the migration of Al and Ni. The Manning dynamic correlation factor is evaluated and found to be close to unity. The predicted interdiffusion coefficients using the Darken equation agree well with experimental data in the literature. [Copyright &y& Elsevier]

Abstract: The effects of spin structures on the Fermi surface topologies of BaFe2As2 were calculated using the first-principles approach. Here, we considered the nonmagnetic, Checkerboard, Stripe, and SDW (spin-density-wave) structures as well as a tetragonal structure labeled as STR17. By comparing the calculated results with the published angle-resolved photoemission spectroscopy from the literature, we propose that most of the experimentally observed Fermi surfaces of BaFe2As2 are the thermal mixture of those of the SDW, STR17, and Stripe structures. [ABSTRACT FROM AUTHOR]

Highlights: [•] Charge ordering is quantitatively predicted in terms of Born effective charge. [•] Charge differences between the disproportionated Fe ions are ∼2e in CaFeO3. [•] Fe3O4 is understood by the charge separation ∼2e instead of ∼1e. [ABSTRACT FROM AUTHOR]

Abstract: Ab initio molecular dynamics (AIMD) calculations were performed on the atomic configuration of Zr41.2Ti13.8Cu12.5Ni10Be22.5 bulk metallic glass. The local structures were characterized in terms of structure factors (SF), pair correlation functions (PCF), coordinate numbers, bond pairs and Voronoi polyhedra. The glass transition temperature, generalized PCF and SF predicated by AIMD are in good agreement with the experimental data. Icosahedral short-range orders (ISRO) are found to be the most dominant, in view of the presence of the majority of bond pairs with 1551, 1541 and 1431, and Voronoi polyhedra with <0,3,6,1>, <0,2,8,1>, <0,0,12,0> and <0,2,8,4>. Icosahedral medium range orders (IMROs) are formed from icosahedra via the linkage of vertex-, edge-, face- and intercross-shared atoms. The glass structure on the nanometer scale is accumulated by polyhedra through an efficient packing mode. It is suggested that the extraordinary glass-forming ability of this alloy is essentially attributable to the formation of ISRO and IMRO, and the dense packing of atoms. [Copyright &y& Elsevier]

Abstract: The atomic configurations of liquid and glassy Mg65Cu25Y10 alloy have been simulated in the temperature range of 300 K to 2000 K via ab initio molecular dynamics. The variations of pair correlation function (PCF), structure factor (SF), coordination number (CN) and bond pairs with the temperature for this alloy are characterized. It has been shown that the atoms are near densely packed and icosahedral type of short-range order (SRO) is predominant in the glass state. Icosahedral medium range order (MRO) can be formed by vertex or intercross connection of icosahedral SROs. In this work, an icosahedral MRO which is composed of 55 atoms has been found. It has been also clarified that Mg and Cu occupy the centre or vertex, and Y atoms only occupy the vertex of the icosahedron in this glassy alloy. It is believed that these findings have implication for understanding the glass forming mechanism of magnesium based metallic glasses. [Copyright &y& Elsevier]