234 research outputs found
The influence of transition metal solutes on dislocation core structure and values of Peierls stress and barrier in tungsten
Several transition metals were examined to evaluate their potential for
improving the ductility of tungsten. The dislocation core structure and Peierls
stress and barrier of screw dislocations in binary
tungsten-transition metal alloys (WTM) were investigated using
first principles electronic structure calculations. The periodic quadrupole
approach was applied to model the structure of dislocation. Alloying
with transition metals was modeled using the virtual crystal approximation and
the applicability of this approach was assessed by calculating the equilibrium
lattice parameter and elastic constants of the tungsten alloys. Reasonable
agreement was obtained with experimental data and with results obtained from
the conventional supercell approach. Increasing the concentration of a
transition metal from the VIIIA group, i.e. the elements in columns headed by
Fe, Co and Ni, leads to reduction of the elastic constant and
increase of elastic anisotropy A=. Alloying W with a group
VIIIA transition metal changes the structure of the dislocation core from
symmetric to asymmetric, similar to results obtained for WRe
alloys in the earlier work of Romaner {\it et al} (Phys. Rev. Lett. 104, 195503
(2010))\comments{\cite{WRECORE}}. In addition to a change in the core symmetry,
the values of the Peierls stress and barrier are reduced. The latter effect
could lead to increased ductility in a tungsten-based
alloy\comments{\cite{WRECORE}}. Our results demonstrate that alloying with any
of the transition metals from the VIIIA group should have similar effect as
alloying with Re.Comment: 12 pages, 8 figures, 3 table
Thickness dependence of the resistivity of Platinum group metal thin films
We report on the thin film resistivity of several platinum-group metals (Ru,
Pd, Ir, Pt). Platinum-group thin films show comparable or lower resistivities
than Cu for film thicknesses below about 5\,nm due to a weaker thickness
dependence of the resistivity. Based on experimentally determined mean linear
distances between grain boundaries as well as ab initio calculations of the
electron mean free path, the data for Ru, Ir, and Cu were modeled within the
semiclassical Mayadas--Shatzkes model [Phys. Rev. B 1, 1382 (1970)] to assess
the combined contributions of surface and grain boundary scattering to the
resistivity. For Ru, the modeling results indicated that surface scattering was
strongly dependent on the surrounding material with nearly specular scattering
at interfaces with SiO2 or air but with diffuse scattering at interfaces with
TaN. The dependence of the thin film resistivity on the mean free path is also
discussed within the Mayadas--Shatzkes model in consideration of the
experimental findings.Comment: 28 pages, 9 figure
Detection of Time-Reversal Symmetry Breaking in the Noncentrosymmetric Superconductor ReZr Using Muon-Spin Spectroscopy
We have investigated the superconducting state of the non-centrosymmetric compound ReZr using magnetization, heat capacity, and muon-spin relaxation/rotation (SR) measurements. ReZr has a superconducting transition temperature, T = 6.75±0.05 K. Transverse-field SR experiments, used to probe the superfluid density, suggest an -wave character for the superconducting gap. However, zero and longitudinal-field SR data reveal the presence of spontaneous static magnetic fields below indicating that time-reversal symmetry is broken in the superconducting state and an unconventional pairing mechanism. An analysis of the pairing symmetries identifies the ground states compatible with time-reversal symmetry breaking
2nd and 3rd Annual Conferences on Metallurgy, Physical Chemistry and Metal Physics of Superconductors
Effect of porosity on the volume changes experienced by Al-Cu compacts during liquid-phase sintering
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