Naval Surface Warfare Center

About: Naval Surface Warfare Center is a facility organization based out in Washington D.C., District of Columbia, United States. It is known for research contribution in the topics: Sonar & Radar. The organization has 2855 authors who have published 3697 publications receiving 83518 citations. The organization is also known as: NSWC.

Structural characterisation of the highly deintercalatedLixNi1.02O2 phases (with x ≤ 0.30)

Abstract: The full structural characterisation of the highly deintercalated LixNi1.02O2 (x ≤ 0.30) phases has been performed. The structure of the Li0.30Ni1.02O2 phase was refined by the Rietveld method. The cationic distribution was found to be identical to that of the pristine material. A study of the Li//LixNi1.02O2 system at high potential has shown the successive formation of two phases with O3 (AB CA BC) and O1 (AB) oxygen packing, respectively, near the NiO2 composition. Since slab gliding is at the origin of the O3 to O1 transition, layer displacement faults were observed in these two phases. For the O3 phase, as soon as all the lithium ions are removed from an interslab space, an O1-type fault occurs locally. In contrast, for the O1 phase, the presence of extra-nickel ions in the interslab space prevents slab gliding in the vicinity and, therefore, O3-type interslab spaces remain in the O1-type packing. The X-ray diffraction patterns were simulated using the DIFFaX program. It was shown that the stabilisation of the O1-type packing at the very end of the deintercalation process is due to a minimisation of the interactions between the p orbitals of the oxygen ions through the van der Waals gap. A two-phase domain is observed between Li0.30NiO2 and a composition close to NiO2 since, for very low lithium contents, the Ni3+/Ni4+ ordering (and the lithium/vacancy ordering) is no longer possible and the difference in size between the cations leads to the formation of constraints which destabilise the Ni3+ ions in a lattice where Ni4+ ions prevail. At the end of the deintercalation process, the NiO2 compound appears to be highly covalent, therefore, the steric effects prevail over the electrostatic repulsion effects, as in chalcogenides.

Structure, Bonding, and Catalytic Activity of Monodisperse, Transition-Metal-Substituted CeO2 Nanoparticles

Abstract: We present a simple and generalizable synthetic route toward phase-pure, monodisperse transition-metal-substituted ceria nanoparticles (M0.1Ce0.9O2–x, M = Mn, Fe, Co, Ni, Cu). The solution-based pyrolysis of a series of heterobimetallic Schiff base complexes ensures a rigorous control of the size, morphology and composition of 3 nm M0.1Ce0.9O2–x crystallites for CO oxidation catalysis and other applications. X-ray absorption spectroscopy confirms the dispersion of aliovalent (M3+ and M2+) transition metal ions into the ceria matrix without the formation of any bulk transition metal oxide phases, while steady-state CO oxidation catalysis reveals an order of magnitude increase in catalytic activity with copper substitution. Density functional calculations of model slabs of these compounds confirm the stabilization of M3+ and M2+ in the lattice of CeO2. These results highlight the role of the host CeO2 lattice in stabilizing high oxidation states of aliovalent transition metal dopants that ordinarily would b...

Magnetostriction of binary and ternary Fe–Ga alloys

Abstract: This article will review the development of the Fe–Ga (Galfenol) alloy system for magnetostriction applications including work on substitutional ternary alloying additions for magnetic property enhancement. A majority of the alloying addition research has focused on substitutional ternary elements in Bridgman grown single crystals with the intent of improving the magnetostrictive capability of the Galfenol system. Single crystals provide the ideal vehicle to assess the effectiveness of the addition on the magnetostrictive properties by eliminating grain boundary effects, orientation variations, and grain-to-grain interactions that occur when polycrystals respond to applied magnetic fields. In almost all cases, ternary additions of transition metal elements have decreased the magnetostriction values from the binary Fe–Ga alloy. Most of the ternary additions are known to stabilize the D03 chemical order and could be a primary contribution to the observed reduction in magnetostriction. In contrast, both Sn and Al are found to substitute chemically for Ga. For Sn additions, whose solubility is limited, no reduction in magnetostriction strains are observed when compared to the equivalent binary alloy composition. Aluminum additions, whose effect on the magnetoelastic coupling on Fe is similar to Ga, result in a rule of mixture relationship. The reviewed research suggests that phase stabilization of the disordered bcc structure is a key component to increase the magnetostriction of Fe–Ga alloys.