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Full-Text Articles in Physics
Origin Of The 〈11/20〉 Atomic Short-Range Order In Au-Rich Au-Fe Alloys, M. F. Ling, J. B. Staunton, Duane D. Johnson, F. J. Pinski
Origin Of The 〈11/20〉 Atomic Short-Range Order In Au-Rich Au-Fe Alloys, M. F. Ling, J. B. Staunton, Duane D. Johnson, F. J. Pinski
Duane D. Johnson
We have calculated the atomic short-range order (ASRO) and paramagnetic susceptibility in high-temperature, chemically disordered Au75Fe25 and Au90Fe10, using a density-functional-based, electronic-structure method. For both alloys, we obtain 〈11/20〉-type ASRO, in excellent agreement with experiments performed on samples that have been fast quenched from high temperature. We also identify the underlying electronic mechanism responsible for this unusual ordering behavior. During annealing at high temperatures, we suggest that aligning local moments via an external magnetic field will produce interesting AuFe alloys with 〈100〉-type ASRO.
Van Hove Singularity Induced L11 Ordering In Cupt, J. F. Clark, F. J. Pinski, Duane D. Johnson, P. A. Sterne, J. B. Staunton, B. Ginatempo
Van Hove Singularity Induced L11 Ordering In Cupt, J. F. Clark, F. J. Pinski, Duane D. Johnson, P. A. Sterne, J. B. Staunton, B. Ginatempo
Duane D. Johnson
We describe an ordering mechanism that arises due to coupling between electronic states at van Hove singularities. This novel mechanism, which naturally leads to ordered structures with small unit cells, couples states near the Fermi energy which are localized at high-symmetry points in k space, in contrast to the conventional mechanism which relies on large parallel sheets of Fermi surface. Using first-principles calculations of the electronic structure of ordered and disordered alloys, we show that this mechanism drives the unusual short- and long-range order found in fcc CuPt.
Commensurate And Incommensurate Ordering Tendencies In The Ternary Fcc Cu-Ni-Zn System, J. D. Althoff, Duane D. Johnson, F. J. Pinski
Commensurate And Incommensurate Ordering Tendencies In The Ternary Fcc Cu-Ni-Zn System, J. D. Althoff, Duane D. Johnson, F. J. Pinski
Duane D. Johnson
We show that Fermi-surface (FS) nesting drives both the incommensurate and commensurate ordering tendencies of the fcc ternary Cu-Ni-Zn system. Surprisingly, commensurate order persists over a wide range of composition, despite its origins. For Cu2NiZn, we discuss how FS nesting and the other effects of alloying lead to ordering tendencies consistent with the experimentally observed order-disorder transformations. All calculations are based on a first-principles theory of the atomic short-range order in alloys with an arbitrary number of components.
Absolute Integrated Cross Sections For Some O2 Herzberg I Transitions Near 248–249 Nm, Zhen-Chuan Bao, Edward Yu, John R. Baker
Absolute Integrated Cross Sections For Some O2 Herzberg I Transitions Near 248–249 Nm, Zhen-Chuan Bao, Edward Yu, John R. Baker
Edward Yu
A frequency doubled tunable dye laser system with ∼0.4 cm−1 resolution was used to measure the integrated absorption cross sections of more than 20 rotational transitions in the O2 Herzberg I (A 3Σ+ u ←X 3Σ− g ) 8‐0 and 9‐0 vibrational bands near 248 nm and 249 nm. Oxygen pressures from 200 to 800 Torr and path lengths from 5 to 25 m were employed. The measured absorbances were fitted using a nonlinear least squares analysis and Beer’s Law to obtain absolute values for the individual transition integrated cross sections in good agreement with a recent spectral simulation and …