A melt has greater volume than a silicate solid of the same composition. But this difference diminishes at high pressure, and the possibility that a melt sufficiently enriched in the heavy element iron might then become more dense than solids at the pressures in the interior of the Earth (and other terrestrial bodies) has long been a source of considerable speculation. The occurrence of such dense silicate melts in the Earth's lowermost mantle would carry important consequences for its physical and chemical evolution and could provide a unifying model for explaining a variety of observed features in the core-mantle boundary region. Recent theoretical calculations combined with estimates of iron partitioning between (Mg,Fe)SiO(3) perovskite and melt at shallower mantle conditions suggest that melt is more dense than solids at pressures in the Earth's deepest mantle, consistent with analysis of shockwave experiments. Here we extend measurements of iron partitioning over the entire mantle pressure range, and find a precipitous change at pressures greater than ∼76 GPa, resulting in strong iron enrichment in melts. Additional X-ray emission spectroscopy measurements on (Mg(0.95)Fe(0.05))SiO(3) glass indicate a spin collapse around 70 GPa, suggesting that the observed change in iron partitioning could be explained by a spin crossover of iron (from high-spin to low-spin) in silicate melt. These results imply that (Mg,Fe)SiO(3) liquid becomes more dense than coexisting solid at ∼1,800 km depth in the lower mantle. Soon after the Earth's formation, the heat dissipated by accretion and internal differentiation could have produced a dense melt layer up to ∼1,000 km in thickness underneath the solid mantle. We also infer that (Mg,Fe)SiO(3) perovskite is on the liquidus at deep mantle conditions, and predict that fractional crystallization of dense magma would have evolved towards an iron-rich and silicon-poor composition, consistent with seismic inferences of structures in the core-mantle boundary region.

We used a suite of transmission electron microscopy (TEM) and associated electron spectroscopy methods to examine the local structure and changes in the electronic structure of LinormalNi0.8normalCo0.15normalAl0.05normalO2 positive electrode material. We found a scattered rock-salt phase near grain surfaces and grain boundaries, where Ni3+ turned to Ni2+ , deduced from relative intensity ratios and fine structures of the L2,3 white-line peaks of the transition metals. The spatial distribution of the degraded phase throughout the secondary particle was found using a scanning TEM-electron energy loss spectroscopy spectral imaging technique and multivariate analysis. The degradation process and its relationship to the surface reactions with electrolytes is discussed based on the spatial-distribution map of the degraded phases.

Hematite (α-Fe2O3) is one of the most promising candidates as a photoanode materials for solar water splitting. Owing to the difficulty in suppressing the significant charge recombination, however, the photoelectrochemical (PEC) conversion efficiency of hematite is still far below the theoretical limit. Here we report thick hematite films (∼1500 nm) constructed by highly ordered and intimately attached hematite mesocrystals (MCs) for highly efficient PEC water oxidation. Due to the formation of abundant interfacial oxygen vacancies yielding a high carrier density of ∼1020 cm−3 and the resulting extremely large proportion of depletion regions with short depletion widths (<10 nm) in hierarchical structures, charge separation and collection efficiencies could be markedly improved. Moreover, it was found that long-lived charges are generated via excitation by shorter wavelength light (below ∼500 nm), thus enabling long-range hole transfer through the MC network to drive high efficiency of light-to-energy conversion under back illumination.

Single crystals of pure CT0 are grown from the vapour phase and the structure and morphology of these crystals is studied. By means of X-ray diffractron and TEM measurements five drfferent phases are observed. The observed phases are (from high to low tem~ratures) fee, rhom~hed~i, ideal hcp (c/a = I .63), deformed hcp (c/a= 1.82) and a monoclinic phase. The occurrence of these different phases and the phase transmons IS accounted for in a simple model. For the monoclinic structure a model for the stackmg of the orientationaily ordered molecules in the lattice IS proposed. For both the hcp and fee phases a Lennard-Jones type mteraction potential is used to calculate bond strengths, lattxe energies and the theoretical morphology.

The mechanism for capacity fade of lithium-ion batteries with LinormalNi0.8normalCo0.15normalAl0.05normalO2 as a positive electrode material associated with cycling at elevated temperatures was investigated by the combination of electrochemical and spectroscopic methods. The total capacity fade of the battery after charge/discharge cycle test at 80°C was found to be almost explained by the capacity fade of the positive electrode, which indicates that the degradation of the positive electrode is mainly responsible for capacity fade of the battery at this temperature. Quantitative analyses revealed a strong positive correlation between the capacity fade of the positive electrode and the amount of inactive Ni ions in the active material after the cycling test. It is concluded that the capacity fade is mainly caused by the formation of inactive Ni(II) and Ni(III), presumably associated with oxygen loss in the active materials, which act as obstacles to Li intercalation/deintercalation.