Cu-Au, Ag-Au, Cu-Ag, and Ni-Au intermetallics: First-principles study of temperature-composition phase diagrams and structures

Iamvasant

Applied Surface Science

et al. 2017

CrCuAgN PVD nanocomposite coatings were produced using pulsed DC unbalanced magnetron sputtering. This investigation focuses on the effects of post-coat annealing on the surface morphology, phase composition and nanostructure of such coatings. In coatings with nitrogen contents up to 16 at.%, chromium exists as metallic Cr with N in supersaturated solid solution, even after 300 o C and 500 o C post-coat annealing.Annealing at 300 o C did not obviously change the phase composition of both nitrogen-free and nitrogen-containing coatings; however, 500 o C annealing resulted in significant transformation of the nitrogen-containing coatings. The formation of Ag aggregates relates to the (Cu+Ag)/Cr atomic ratio (threshold around 0.2), whereas the formation of Cu aggregates relates to the (Cu+Ag+N)/Cr atomic ratio (threshold around 0.5). The primary annealing-induced changes were reduced solubility of Cu, Ag and N in Cr, and the composition altering from a mixed ultra-fine nanocrystalline and partly amorphous phase constitution to a coarser, but still largely nanocrystalline structure. It was also found that, with sufficient Cu content (> 12 at.%), annealing at a moderately high temperature (e.g. 500 o C) leads to transportation of both Cu and Ag (even at relatively low concentrations of Ag, ≤ 3 at.%) from inside the coating to the coating surface, which resulted in significant reductions in friction coefficient, by over 50% compared to that of the substrate (from 0.31 to 0.14 with a hemispherical diamond indenter, and from 0.83 to 0.40 with an alumina ball counterface, respectively). Results indicate that the addition of both Cu and Ag (in appropriate *Manuscript Click here to view linked References 2 concentrations) to nitrogen-containing chromium is a viable strategy for the development of 'self-replenishing' silver-containing thin film architectures for temperature-dependent solid lubrication requirements or antimicrobial coating applications.

Section: Edx Line Scan Analysissupporting

confidence: 51%

CrCuAgN PVD nanocomposite coatings: Effects of annealing on coating morphology and nanostructure

Iamvasant

Applied Surface Science

et al. 2017

Modelling Simul. Mater. Sci. Eng.

“…When relaxations are included the ECI become much longer range (the largest ECI is in fact in the fifth-neighbour shell). The introduction of longer-range interactions when relaxations are included has also been found in cluster expansions of the total energy [4,[48][49][50][51]. In addition, in the relaxed case the RMS error is almost constant after the fifthneighbour shell, even though it is about five times as large as the corresponding error in the unrelaxed case.…”

Section: Embedded-atom Methods Study Of Ni 3 Almentioning

confidence: 88%

Vibrational thermodynamics: coupling of chemical order and size effects

Morgan¹,

Walle²,

Ceder³

et al. 2000

Abstract. The effects of chemical order on the vibrational entropy have been studied using firstprinciples and semi-empirical potential methods. Pseudopotential calculations on the Pd 3 V system show that the vibrational entropy decreases by 0.07k B upon disordering in the high-temperature limit. The decrease in entropy contradicts what would be expected from simple bonding arguments, but can be explained by the influence of size effects on the vibrations. In addition, the embeddedatom method is used to study the effects of local environments on the entropic contributions of individual Ni and Al atoms in Ni 3 Al. It is found that increasing numbers of Al nearest neighbours decreases the vibrational entropy of an atom when relaxations are not included. When the system is relaxed, this effect disappears, and the local entropy is approximately uniform with increasing number of Al neighbours. These results are explained in terms of the large size mismatch between Ni and Al. In addition, a local cluster expansion is used to show how the relaxations increase the importance of long-range and multisite interactions.

“…59 While the formation of CuAu is favored by electronegativity arguments and its phase transitions resemble those of SbAs, the question remains why SbAs differs from GeTe. It may be that the vibrational and strain-related contributions to the formation energy are very important in SbAs, as they are in CuAu and NiPt, 60,61 and their effects should be investigated.…”

Section: B Crystal Chemistry and High-temperature Transformationmentioning

confidence: 99%

Chemical ordering rather than random alloying in SbAs

Shoemaker

Chasapis

et al. 2013

Phys. Rev. B

The semimetallic Group V elements display a wealth of correlated electron phenomena due to a small indirect band overlap that leads to relatively small, but equal, numbers of holes and electrons at the Fermi energy with high mobility. Their electronic bonding characteristics produce a unique crystal structure, the rhombohedral A7 structure, which accommodates lone pairs on each site. Here we show via single-crystal and synchrotron x-ray diffraction that SbAs is a compound and the A7 structure can display chemical ordering of Sb and As, which were previously thought to mix randomly. Formation of this compound arises due to differences in electronegativity that are common to IV-VI compounds of average group V such as GeTe, SnS, PbS, and PbTe, and also ordered intra-period compounds such as CuAu and NiPt. High-temperature diffraction studies reveal an order-disorder transition around 550 K in SbAs, which is in stark contrast to IV-VI compounds GeTe and SnTe that become cubic at elevated temperatures but do not disorder. Transport and infrared reflectivity measurements, along with first-principles calculations, confirm that SbAs is a semimetal, albeit with a direct band separation larger than that of Sb or As. Because even subtle substitutions in the semimetals, notably Bi1−xSbx, can open semiconducting energy gaps, a further investigation of the interplay between chemical ordering and electronic structure on the A7 lattice is warranted.