Octahedral Distortion and Displacement-Type Ferroelectricity with Switchable Photovoltaic Effect in a 3d

Because of the half-filled t_{2g}-electron configuration, the BO_{6} octahedral distortion in a 3d^{3} perovskite system is usually very limited. In this Letter, a perovskitelike oxide Hg_{0.75}Pb_{0.25}MnO_{3} (HPMO) with a 3d^{3} Mn^{4+} state was synthesized by using high pressure and high temperature methods. This compound exhibits an unusually large octahedral distortion enhanced by approximately 2 orders of magnitude compared with that observed in other 3d^{3} perovskite systems like RCr^{3+}O_{3} (R=rare earth). Essentially different from centrosymmetric HgMnO_{3} and PbMnO_{3}, the A-site doped HPMO presents a polar crystal structure with the space group Ama2 and a substantial spontaneous electric polarization (26.5 µC/cm^{2} in theory) arising from the off-center displacements of A- and B-site ions. More interestingly, a prominent net photocurrent and switchable photovoltaic effect with a sustainable photoresponse were observed in the current polycrystalline HPMO. This Letter provides an exceptional d^{3} material system which shows unusually large octahedral distortion and displacement-type ferroelectricity violating the "d^{0}-ness" rule.

Flatband in a three-dimensional tungsten nitride compound.

Herein, the flatband of a W1N2 crystal is theoretically investigated. It is revealed that the flatband can be well-described by a tight-binding model of the N12 skeleton, where the dispersion of the flatband is governed by both the ppσ bonding strength (Vppσ) and the ppπ bonding strength (Vppπ) between the nearest-neighbor N atoms. It is also found that the proper strength of the ppπ bonding between neighboring N atoms plays a prime role in the formation of the flatband. In addition, when the compound is doped with holes, the electrons at the flatband are fully polarized, showing a ferromagnetic character. This behavior has a weak correlation with the on-site Coulomb interaction U. Moreover, several three-dimensional compounds possessing flatbands in the whole k space are predicted.

A machine learning based deep potential for seeking the low-lying candidates of Al clusters.

A Machine-Learning based Deep Potential (DP) model for Al clusters is developed through training with an extended database including ab initio data of both bulk and several clusters in only 6 CPU/h. This DP model has good performance in accurately predicting the low-lying candidates of Al clusters in a broad size range. Based on our developed DP model, the low-lying structures of 101 different sized Al clusters are extensively searched, among which the lowest-energy candidates of 69 sized clusters are updated. Our calculations demonstrate that machine-learning is indeed powerful in generating potentials to describe the interaction of atoms in complex materials.

Linear scaling algorithm for tight-binding molecular dynamics simulations.

The linear scaling or O(N) methods, which exhibit linear scaling with respect to the size of system, are a powerful tool for theoretically treating a huge system containing many atoms. We present a new linear scaling algorithm for large-scale tight-binding molecular dynamics simulations based on the divide-and-conquer approach, in which a system is divided into subsystems and each subsystem is calculated separately. Different from the common realization of the divide-and-conquer approach, our proposed method avoids building the density matrix or electronic density and gives a new strategy to access the physical properties of a large system. We apply this method to the tungsten metallic system and show that this method very effectively yields the same results including the atomic structures, the melting point, the formation energy of defects, and the electronic properties as those obtained from the exact diagonalization of tight-binding Hamiltonian matrix of a whole system. This method has the advantages of linear scaling complexity, less memory consumption, and high parallel efficiency, which make it to be used for the large-scale simulations.

Combination of edaravone and neural stem cell transplantation repairs injured spinal cord in rats.

This study sought to observe the effect of the combination of edaravone and neural stem cell (NSC) transplantation on the repair of complete spinal cord transection in rats. Eighty adult female Sprague-Dawley (SD) rats were used to establish the injury model of complete spinal cord transection at T9. Animals were divided randomly into four groups (N = 20 each): control, edaravone, transplantation, and edaravone + transplantation. The recovery of spinal function was evaluated with the Basso, Beattie, Bresnahan (BBB) rating scale on days 1, 3, and 7 each week after the surgery. After 8 weeks, the BBB scores of the control, edaravone, transplantation, and combination groups were 4.21 ± 0.11, 8.46 ± 0.1, 8.54 ± 0.13, and 11.21 ± 0.14, respectively. At 8 weeks after surgery, the spinal cord was collected; the survival and transportation of transplanted cells were observed with PKH-26 labeling, and the regeneration and distribution of spinal nerve fibers with fluorescent-gold (FG) retrograde tracing. Five rats died due to the injury. PKH-26-labeled NSCs had migrated into the spinal cord. A few intact nerve fibers and pyramidal neurons passed the injured area in the transplantation and combination groups. The numbers of PKH-26-labeled cells and FG-labeled nerve fibers were in the order: combination group > edaravone group and transplantation group > control group (P < 0.05 for each). Thus, edaravone can enhance the survival and differentiation of NSCs in injured areas; edaravone with NSC transplantation can improve the effectiveness of spinal cord injury repair in rats.

A study on oxidative stress in lead-exposed workers.

To explore the possible oxidative stress induced by lead, heparinized whole blood and urine of 66 secondary smelter lead workers (46 for Comet assay) and 28 controls were collected. The concentrations of blood lead (BPb) and urinary lead (UPb) and alpha-aminolevulinic acid (alpha-ALA), indices of lead exposure level of the body, were determined. Malondialdehyde (MDA) concentrations and superoxide dismutase (SOD) activity of plasma were also measured. Single-cell gel (SCG, Comet assay) was used to measure the DNA damage of peripheral blood cells. There was a positive correlation between the presence of Pb in blood and significant increases in MDA levels and SOD activity. Alcohol consumption and smoking with increased exposure to Pb was associated with enhanced DNA damage. A positive correlation was found between MDA and DNA damage.