Phase Segregation via Etching-Induced Cation Migration in CoSx-ZnS Nanoarchitectures for Solar Hydrogen Evolution

Low charge carrier mobility limits the development of highly efficient semiconductor-based photocatalysis. Heterointerface engineering is a promising approach to spatially separate the photoexcited charge carriers and thus enhance photocatalytic activity....

New insights in the mechanism of cation migration induced by cation-anion dynamic coupling in superionic conductors

Understanding the ion diffusion mechanism is one of the key preconditions for designing superionic conductors in solid state lithium batteries and many other energy devices. Besides single-cation vacancy/interstitial-assisted and multi-cation...

Polyol-Made Spinel Ferrite Nanoparticles—Local Structure and Operating Conditions: NiFe2O4 as a Case Study

We report the effect of a polyol-mediated annealing on nickel ferrite nanoparticles. By combining X-ray fluorescence spectroscopy, X-ray diffraction, and 57Fe Mössbauer spectrometry, we showed that whereas the as-prepared nanoparticles (NFO) are stoichiometric, the annealed ones (a-NFO) are not, since Ni0-based crystals precipitate. Nickel depletion from the spinel lattice and reduction in the polyol solvent are accompanied with an important cation migration. Indeed, thanks to Mössbauer hyperfine structure analysis, we evidenced that the cation distribution in NFO departs from the thermodynamically stable inverse spinel structure with a concentration of tetrahedrally coordinated Ni2+ of 20 wt-% (A sites). After annealing, and nickel demixing, originated very probably from the A sites of NFO lattice, the spinel phase accommodates with cation and anion vacancies, leading to the (Fe3+0.84□0.16)A[Ni2+0.80Fe3+1.16□0.04]BO4-0.20 formula, meaning that the applied polyol-mediated treatment is not so trivial.

Thermodilatometric Study of the Decay of Zeolite-Bearing Building Materials

Six zeolite-bearing rocks, often used as building materials, were analyzed by thermodilatometry, together with a rock not bearing zeolites and a plaster covering a containing wall made of zeolite-bearing dimension stones, up to 250 °C. The main results obtained were the following: (i) the zeolite-bearing rocks exhibited very small, if any, positive variation of ΔL/Lo (%) up to about 100 °C, whereas they more or less shrank in the temperature range 100–250 °C (final values ranging from −0.21 to −0.92%); (ii) the rock not bearing zeolites regularly expanded through the whole temperature range, attaining a final value of 0.19%; (iii) the plaster showed a thermodilatometric behavior strongly affected by its water content. Obtained results were interpreted based on plain thermal expansion, shrinkage by dehydration, cation migration and thermal collapse of the zeolitic structure. The decay of the zeolite-bearing building materials was essentially related to: (i) the large differences recorded in the thermodilatometric behavior of the various rocks and the plaster; (ii) the different minerogenetic processes that resulted in the deposition of the various zeolite-bearing rocks.

Addressing voltage decay in Li-rich cathodes by broadening the gap between metallic and anionic bands

Oxygen release and irreversible cation migration are the main causes of voltage fade in Li-rich transition metal oxide cathode. But their correlation is not very clear and voltage decay is still a bottleneck. Herein, we modulate the oxygen anionic redox chemistry by constructing Li2ZrO3 slabs into Li2MnO3 domain in Li1.21Ni0.28Mn0.51O2, which induces the lattice strain, tunes the chemical environment for redox-active oxygen and enlarges the gap between metallic and anionic bands. This modulation expands the region in which lattice oxygen contributes capacity by oxidation to oxygen holes and relieves the charge transfer from anionic band to antibonding metal–oxygen band under a deep delithiation. This restrains cation reduction, metal–oxygen bond fracture, and the formation of localized O2 molecule, which fundamentally inhibits lattice oxygen escape and cation migration. The modulated cathode demonstrates a low voltage decay rate (0.45 millivolt per cycle) and a long cyclic stability.

Stepwise dehydration of Cd-exchanged levyne: thermal stability and structural modifications

Zeolites show remarkable properties that can be tuned through cation exchange of their original extraframework content. In this respect, the response of the modified zeolite to the heating stimuli, in terms of structural modifications and thermal stability, can drastically change and is, therefore, an important factor to consider. In this study, the dehydration mechanism of a natural levyne previously exchanged with Cd2+ has been monitored in situ by single crystal X-ray diffraction. The initial dehydration trend between 50 and 175 °C is similar to that observed for the pristine material, levyne-Ca. The water loss is accompanied by extraframework cation migration within the zeolitic cavities and the unit-cell volume slightly contracts from 3503.8(1) to 3467.8(6) Å3. From 200 to 250 °C, a pronounced drop of the unit-cell volume (− 7%) is observed. The dehydrated structure at 250 °C corresponds to levyne B topology of natural levyne, characterized by the statistical rupture of the T–O–T bonds of the double six-ring membered cage. However, in contrast to levyne-Ca, the fraction of broken connections reached 50% instead of 37%, and no additional structural modifications were detected up to 350 °C. At 400 °C, diffraction data pointed to the onset of the structural collapse. At this temperature, the measured unit-cell volume was 8% smaller compared to that of the RT structure. The corresponding contracted structure did not rehydrate after exposure to humid conditions for 21 days.