Ni-rich Structure Research Articles

A comparative study of structural changes in lithium nickel cobalt manganese oxide as a function of Ni content during delithiation process

First-principles calculations and in-situ X-ray diffraction (XRD) experiment have been performed to investigate the structural changes and potential oxygen evolution in Li(Ni(y)Co(1−y)/2Mn(1−y)/2)O2 (y = 0.33, 0.56, and 0.78) and LiNiO2 cathode materials during electrochemical activities. They reveal that as the Ni content is increased, the change in lattice parameters becomes more significant during charging, which could induce the mechanical degradation in the cathode. Detailed analysis of delithiation process demonstrates the origin of the characteristic variations in the lattice parameters. Open-circuit voltage (OCV) calculations and charge–discharge experiments suggest that at the same voltage, more Li ions are extracted from Ni-rich structures, leading to further structural instability. Atomic charge analysis indicates that Ni mainly participates in charge compensation process in the practical range of delithiation, and then Co covers after further severe Li extraction. With increasing Ni content, the oxidation of oxygen, which is initially more oxidized, is accelerated during charging; this result explains the poorer oxygen stability observed in Ni-rich structures.

Morphological and compositional features of blue and yellow pigments used in Portuguese glazed ceramics by SEM/EDX – unravelling manufacturing differences

Morphological and compositional features regarding blue and yellow pigments used in glazed ceramics from Portugal are investigated by means of a SEM/EDX system. Fragments of samples produced in the main pottery-making centres between the XVI–XVIII centuries (Lisbon and Coimbra) were the objects of study. The main question to be answered is whether there are differences in the manufacturing procedures employed. For this purpose, two types of samples were analysed: faiences and wall-tiles (the famous “Azulejos”, in Portuguese). Differences between the manufacturing techniques of the two production centres were veritably found. The expected linkage between Fe–Co–Ni–As–Bi was challenging to investigate. Thus, Co was found in Fe- or Ni-rich structures, but with no structural connection to As or Bi. However, the As-needle-like structures were always identified in blue regions. One interesting finding related particularly to the blue pigment was the presence of SnO2 agglomerates throughout the whole glaze, which suggests its intentional addition for “lightening” the well known dark Co blue. Concerning the yellow pigment differences established in the crystal shape and size are indicative of different firing temperatures used.

Theoretical Determination of the Most Stable Structures of NimAgn Bimetallic Nanoalloys

The structure of the global total-energy minimum for all bimetallic NimAgn nanoalloys with m + n = N = 2−60 atoms has been identified theoretically by combining the embedded-atom model for the total-energy evaluation with the basin-hopping algorithm for global structure optimization. All global minima structures are found to be related to icosahedra and polyicosahedra, except for some Ni- or Ag-rich clusters for N = 38. Through a careful analysis of the total energy as a function of (m,n), various particularly stable structures can be identified. The results show in most cases that Ag-rich structures are more favored and stable compared with the Ni-rich structures. By analyzing the bond-order parameter and the radial distances, we can demonstrate the existence of core−shell structures with a partial segregation of Ag to the surface of the Ni−Ag clusters.

Cell-constrained melt-quench simulation of d-AlCoNi: Ni-rich versus Co-rich structures

Complex crystalline ground state structures may be obtained by direct (simulated) quenches from the melt for systems of up to a few hundred atoms, given the constraint of a fixed unit cell, coupled with use of (i) replica-exchange Monte Carlo, and (ii) realistic empirical interaction pair potentials. We applied this procedure to decagonal approximants of Al72Co8Ni20 and Al73Co27, obtaining the best energies seen to date for d-AlCoNi models (respectively +20 meV/atom and +9 meV/atom above the tie-plane of competing phases). We elucidated the reasons why different decagonal structures are associated with the Ni-rich and Co-rich compositions. We found a cell doubling to c = 8 Å due to layer puckering not only in the Co-rich structure, but (locally) in the nominally c = 4 Å Ni-rich structure.

電析Ｎｉ‐Ｐ合金めっきの熱処理による皮膜構造変化と硬さとの関係

Electroplated Ni-P films with a range of P contents were prepared an electroplating method based on a Watt type bath. Vicker's hardness of each specimen was measured after annealing at 200-800°C. The hardening mechanisms for the Ni-5wt%P and Ni-11wt%P films were studied in detail by X-ray diffraction, scanning electron microscopy and transmission electron microscopy. Hardness of the Ni-5wt%P film increased gradually at annealing temperatures up to 400°C and then decreased at higher annealing temperatures. The hardness of the Ni-11wt%P films, on the other hand, showed no increase at annealing temperatures up to 300°C, and a sudden increase at 400°C, with no further change at higher annealing temperatures.The mechanisms of hardening were different for the two films. As-plated Ni-11wt%P film had an amorphous structure, while hardened specimens exhibited the two phase structure of Ni3P-Ni with an Ni3P matrix, and its hardening is attributed to the formation of Ni3P. As-plated 5wt%P film had an f. c. c structure, and the specimens annealed at 400°C showed little structural change except for a gradual increase in the lattice parameter as annealing time increased, indicating that oversaturated P is excluded from the Ni lattice. Given that no Ni3P precipitates were observed, it was concluded that segregation of P to the grain boundaries was the mechanism of hardening. The softening of this film at 800°C was considered to be due to the formation of an Ni-rich structure containing the Ni3P phase.