There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

https://dc.engconfintl.org/cgi/viewcontent.cgi?article=1032&context=superalloys_ii

A critical review of high entropy alloys and related concepts

Microstructures and properties of high-entropy alloys

The pace of materials discovery for heterogeneous catalysts and electrocatalysts could, in principle, be accelerated by the development of efficient computational screening methods. This would require an integrated approach, where the catalytic activity and stability of new materials are evaluated and where predictions are benchmarked by careful synthesis and experimental tests. In this contribution, we present a density functional theory-based, high-throughput screening scheme that successfully uses these strategies to identify a new electrocatalyst for the hydrogen evolution reaction (HER). The activity of over 700 binary surface alloys is evaluated theoretically; the stability of each alloy in electrochemical environments is also estimated. BiPt is found to have a predicted activity comparable to, or even better than, pure Pt, the archetypical HER catalyst. This alloy is synthesized and tested experimentally and shows improved HER performance compared with pure Pt, in agreement with the computational screening results.

Computational high-throughput screening of electrocatalytic materials for hydrogen evolution

http://ronald-wagner.de/diss/html/lit/share/surfsci411(98)186.pdf

The surface energy of metals

A first principles study of the stacking fault energies for fcc Co-based binary alloys

Using the ab initio exact muffin-tin orbitals method in combination with the coherent-potential approximation, we have calculated the elastic parameters of ferromagnetic ${\text{Fe}}_{1\ensuremath{-}m}{\text{Mg}}_{m}$ $(0\ensuremath{\le}m\ensuremath{\le}0.1)$ and ${\text{Fe}}_{1\ensuremath{-}c}{\text{Cr}}_{c}$ $(0\ensuremath{\le}c\ensuremath{\le}0.2)$ random alloys in the body-centered cubic (bcc) crystallographic phase. Results obtained for ${\text{Fe}}_{1\ensuremath{-}c}{\text{Cr}}_{c}$ demonstrate that the employed theoretical approach accurately describes the experimentally observed composition dependence of the polycrystalline elastic moduli of Fe-rich alloys encompassing maximum $\ensuremath{\sim}10%$ Cr. The elastic parameters of Fe-Cr alloys are found to exhibit anomalous composition dependence around 5% Cr. The immiscibility between Fe and Mg at ambient conditions is well reproduced by the present theory. The calculated lattice parameter for the Fe-Mg regular solid solution increases by $\ensuremath{\sim}1.95%$ when 10% Mg is introduced in Fe, which corresponds approximately to 11% decrease in the average alloy density, in perfect agreement with the experimental finding. At the same time, we find that all of the elastic parameters of bcc Fe-Mg alloys decrease almost linearly with increasing Mg content. The present results show a much stronger alloying effect for Mg on the elastic properties of $\ensuremath{\alpha}\text{-Fe}$ than that for Cr. Our results call for further experimental studies on the mechanical properties of the Fe-Mg system.

Ab initio calculations of elastic properties of bcc Fe-Mg and Fe-Cr random alloys

The physics and chemistry of the actinide elements form the scientific basis for rational handling of nuclear materials(1-3). In recent experiments(4), most unexpectedly, plutonium dioxide has been ...

Oxidation of plutonium dioxide.

The stability of cubic ${\mathrm{CaSiO}}_{3}$ perovskite with respect to octahedral rotations is investigated by ab initio total-energy calculations. The proposed theoretical ground-state crystal structure has the orthorhombic Pbnm symmetry. Pressure gradually reduces the average tilting of the ${\mathrm{SiO}}_{6}$ octahedra relative to the cubic axis, from 7\ifmmode^\circ\else\textdegree\fi{} at zero pressure to 4\ifmmode^\circ\else\textdegree\fi{} at about 150 GPa. The energy difference between the orthorhombic and cubic phases at 0 GPa is 63 meV per f.u. and shows weak pressure dependence. A possible stabilization of the cubic phase at finite temperatures by entropy effects is discussed.

Levente Vitos

Papers

A first principles study of the stacking fault energies for fcc Co-based binary alloys

Ab initio calculations of elastic properties of bcc Fe-Mg and Fe-Cr random alloys

Oxidation of plutonium dioxide.

Low-temperature crystal structure of CaSiO3 perovskite : An ab initio total energy study

Magnetic phase diagram of the Fe-Ni system