Pressure-Induced Phase Transition and Compression Properties of HfO2 Nanocrystals.

Nanoparticles exhibit unique properties due to their surface effects and small size, and their behavior at high pressures has attracted widespread attention in recent years. Herein, a series of in situ high-pressure X-ray diffraction measurements with a synchrotron radiation source and Raman scattering have been performed on HfO2 nanocrystals (NC-HfO2) with different grain sizes using a symmetric diamond anvil cell at ambient temperature. The experimental data reveal that the structural stability, phase transition behavior, and equation of state for HfO2 have an interesting size effect under high pressure. NC-HfO2 quenched to normal pressure is characterized by transmission electron microscopy to determine the changing behavior of grain size during phase transition. We found that the rotation of the nanocrystalline HfO2 grains causes a large strain, resulting in the retention of part of an orthorhombic I (OI) phase in the sample quenched to atmospheric pressure. Furthermore, the physical mechanism of the phase transition of NC-HfO2 under high pressure can be well explained by the first-principles calculations. The calculations demonstrate that NC-HfO2 has a strong surface effect, that is, the surface energy and surface stress can stabilize the structures. These studies may offer new insights into the understanding of the physical behavior of nanocrystal materials under high pressure and provide practical guidance for their realization in industrial applications.

An Innovative Insight into Performance Degradation of NCM111 Cathode Induced by Suspension of Operation.

The lifespan of lithium-ion batteries varies enormously from fundamental study to practical applications. This big difference has been typically ascribed to the high degree of uncertainty in unpredictable and complicated operation conditions in real-life applications. Here, we report that the pause of the charging-discharging process, which is frequently operated in practice but rarely studied in academics, is an important reason for the performance degradation of the NCM111 cathode. It is found that the pause during cycling could trigger a remarkable drop in capacity, giving rise to ∼30% more capacity decay compared with the continuously cycled sample. In situ synchrotron X-ray diffraction analysis reveals that the harmful H1-H2 phase transition, which typically appears in the initial cycle but disappears in subsequent cycles, is reactivated by the pausing process. The anisotropic lattice strains that occur during the H1-H2 transition result in mechanical fractures that terminate with an inert NiO-type rock-salt phase on the surface of particles. The present study indicates that the discontinuous usage of rechargeable batteries is also a key factor for cycle life, which might provide a distinct perspective on the performance decay in practical applications.

Creating two-dimensional solid helium via diamond lattice confinement.

The universe abounds with solid helium in polymorphic forms. Therefore, exploring the allotropes of helium remains vital to our understanding of nature. However, it is challenging to produce, observe and utilize solid helium on the earth because high-pressure techniques are required to solidify helium. Here we report the discovery of room-temperature two-dimensional solid helium through the diamond lattice confinement effect. Controllable ion implantation enables the self-assembly of monolayer helium atoms between {100} diamond lattice planes. Using state-of-the-art integrated differential phase contrast microscopy, we decipher the buckled tetragonal arrangement of solid helium monolayers with an anisotropic nature compressed by the robust diamond lattice. These distinctive helium monolayers, in turn, produce substantial compressive strains to the surrounded diamond lattice, resulting in a large-scale bandgap narrowing up to ~2.2 electron volts. This approach opens up new avenues for steerable manipulation of solid helium for achieving intrinsic strain doping with profound applications.

Overview on the Amendments of Provisions for Drug Registration in China.

The revised Provisions for Drug Registration was promulgated by the State Administration for Market Regulation of China in March 2020 and came into force on July 1, 2020. This article describes the history of the drug registration management system in China, explains the background of the revision of the Provisions for Drug Registration in 2020, and introduces the main modifications of the Provisions for Drug Registration in 2020 in the aspects of registration classification, application for clinical trial on drug, application for drug marketing authorization, accelerated procedure for drug registration, working timeline, and supervision and administration. This article is intended to give a brief overview for those who wish to submit a drug registration application in China or for those who would like to get more acquainted with drug registration in China.

Achieving large uniform tensile elasticity in microfabricated diamond.

Diamond is not only the hardest material in nature, but is also an extreme electronic material with an ultrawide bandgap, exceptional carrier mobilities, and thermal conductivity. Straining diamond can push such extreme figures of merit for device applications. We microfabricated single-crystalline diamond bridge structures with ~1 micrometer length by ~100 nanometer width and achieved sample-wide uniform elastic strains under uniaxial tensile loading along the [100], [101], and [111] directions at room temperature. We also demonstrated deep elastic straining of diamond microbridge arrays. The ultralarge, highly controllable elastic strains can fundamentally change the bulk band structures of diamond, including a substantial calculated bandgap reduction as much as ~2 electron volts. Our demonstration highlights the immense application potential of deep elastic strain engineering for photonics, electronics, and quantum information technologies.