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A first-principles approach was utilized to investigate the magnetoelectric coupling behaviour of two-dimensional BaTiO3 (001) ultrathin films with surface Ba vacancy under different strains. The total magnetic moment was suppressed when compressive strains were employed and had minimum values of 1.715 μB and 1.568 μB corresponding to uniaxial and biaxial strains, respectively; moreover, it exhibits an enhancement in the case of tensile strain. For shear strain, the magnetic moment fluctuated at ~1.78 μB. Furthermore, all partial magnetic moments and spontaneous polarization were functions of the strains except for the case of shear strain. Their conversion efficiency exhibited a regular varying tendency with increasing tensile strain. To explore electron spins, which can also be regulated, spin-orbit coupling calculations were carried out, showing that the changes in partial magnetic moments increased when the tensile strain was enhanced. Our study may pave a way for two-dimensional BaTiO3 to be applied in novel spin-based devices.

A first-principles approach is utilized to study the magnetoelectric coupling induced by Fe in two-dimensional BaTiO3(001) ultrathin film. It is observed that the Fe impurity increases the total magnetic moment but suppresses the spontaneous polarization. Furthermore, the total magnetic moment of Fe replacing Ti is influenced by the distance between dopants and decreases with reducing distance. A study of spin-orbit coupling under bi-axial compressive strain shows strong magnetoelectric coupling with Ti substitution and the configuration with neighbouring Fe is more readily adjusted than that with Fe distant from each other. Meanwhile, the replacement of Ba exhibits negligible interaction between spontaneous polarization and magnetic moment. Clearly, our current work may indicate that the careful substitution of Ti with Fe atoms can realize two-dimensional BaTiO3 behaving as a multiferroic material.

A first-principles approach is employed to study the influences of the metal species Al, Zr, Mo and Tc on the mechanical properties of U3Si2. When the Al, Zr, Mo and Tc atoms diffuse into the vacancy sites, they dissolve into the lattice, as confirmed by the solution energies. It is found that the compounds of U3Si2 with low amounts of Al, Zr, Mo, and Tc in the Si vacancies or Al, Zr, and Mo in the U vacancies can behave in the manner of ductility. However, in the cases where Al, Zr, Mo and Tc occupy the interstitial sites, all the compounds are demonstrated to be brittle. Furthermore, the stress-strain relationship for the U3Si1.9375Mo0.0625 system was calculated, which illustrates the enhanced ductility. The current results indicate that the substitution of Si by carefully selected metal atoms can enhance the performance of U3Si2.

The uranium silicide U3Si5 has been utilized as the second phase in the UN-U3Si5 composite fuel. However, there have thus far been few theoretical investigations on its microscopic structure and mechanical behaviors. In this work, the electronic structures, elastic mechanical properties, Debye temperature and defect formation energies of U3Si5 are systematically studied by density functional theory. The crystalline structure of U3Si5 is determined to be a defective β-USi2 with a distorted lattice, in good agreement with the experimental observations. The theoretical results indicate that the U3Si5 is a metallic and brittle material and the chemical bonds in U3Si5 are found similar with those of U3Si2. We have also calculated formation energies of different types of point defects: vacancies, interstitials, and Frenkel pairs in U3Si5. The smaller Si atoms exhibit lower defect formation energies than U atoms with an isolated Si or U atom as the reference. Besides, the silicon vacancies are not prone to cluster. The volumes of supercells with interstitial and Frenkel pair defects are found to increase but single vacancies cause an opposite trend. This work may provide theoretical insights into the behavior of uranium silicide materials under irradiation.

A first-principles approach is utilized to study the magnetoelectric coupling induced by Fe in two-dimensional BaTiO

Defect introduction is one of the most important motivations to produce highly efficient electrocatalyst in the field of water splitting. Here we report the visible-light enhanced photoelectrochemical performance derived from defect-rich ReS2 nanosheets with high activity towards hydrogen generation from water. After continuous pre-electrolysis under visible-light irradiation for about 2 h, the activated ReS2 nanosheets electrocatalyst performs highly enhanced catalytic activity, with an onset potential decreasing from 170 to 88 mV and a long stability over 10 h. It is worth noting that only a small overpotential of 116 mV is required to afford the current density of 10 mA cm−2, which is the highest activity to date for ReS2 electrocatalysts and much better than most transition-metal dichalcogenide materials electrocatalysts. Ex-situ transmission electron microscopy (TEM) and inductively coupled plasma emission spectrometer (ICP) examinations demonstrate that the performance improvement is attributed to the defect introduction during the visible-light assisted pre-electrolysis process involving the rhenium atoms vacancies on the basal planes and the lattice fringes of ReS2. Theoretical calculations further confirm that the abundant Re atoms vacancies with lower Gibbs free energy for H adsorption activate the inert basal plane as highly active sites for hydrogen evolution.

A first-principles approach is employed to study the influences of the metal species Al, Zr, Mo and Tc on the mechanical properties of U3Si2. When the Al, Zr, Mo and Tc atoms diffuse into the vacancy sites, they dissolve into the lattice, as confirmed by the solution energies. It is found that the compounds of U3Si2 with low amounts of Al, Zr, Mo, and Tc in the Si vacancies or Al, Zr, and Mo in the U vacancies can behave in the manner of ductility. However, in the cases where Al, Zr, Mo and Tc occupy the interstitial sites, all the compounds are demonstrated to be brittle. Furthermore, the stress-strain relationship for the U3Si1.9375Mo0.0625 system was calculated, which illustrates the enhanced ductility. The current results indicate that the substitution of Si by carefully selected metal atoms can enhance the performance of U3Si2.

In this work, the multiferroic property of Ba-deficient BaTiO3 (001) ultrathin film is studied employing the first-principles approach. The BaTiO3 (001) ultrathin film is more energetically stable and behaves as a semiconductor relative to the (111) and (101) configurations, confirmed from the surface grand potential and electronic density of states. The electronic structures show that the O vacancy can switch the (001) film from a semi-conductor into a metal, while the Ba defect has a slight influence on the band gap, at a concentration of ~2.13%. In Ba-deficient (001) film, the spontaneous polarization pattern is changed and a spontaneous polarization parallel to the surface is observed. Furthermore, a magnetic moment is induced, and it is found to be originated from the O atoms in the supercell. Our results suggest that a strong magnetoelectric coupling occurs because the magnetic moment exhibits a 43.66% drop when the spontaneous polarization increases from 12.84 &micro, C/cm2 to 23.99 &micro, C/cm2 in the deficient BaTiO3 with m = 2 under the bi-axial compress stress field.

A first-principles approach is employed to study the damage caused by gaseous species, He, Kr, and Xe atoms, on the structures of nuclear fuel U3Si. Formation energies suggest that a U vacancy is more readily generated than is an Si vacancy, and that gaseous atoms, He, Kr, and Xe, favor residing in vacancies compared with interstitial sites. By combining the trapping energies and formation energies of secondary vacancy defects, it can be determined that the number capacity of one U or Si vacancy to trap He atoms in U3Si is two or three, while it is only one with respect to Kr and Xe. When the number of trapped He (Kr and Xe) atoms is increased to four (two), the production of a secondary U vacancy is energetically favorable, and the formation of He (Kr and Xe) bubbles can be initiated. Additionally, when an Xe atom is trapped in an Si vacancy of β-U3Si, Xe bubble evolution is predominantly controlled by diffusion. From this work, one may gain new insight into the mechanism behind bubble formation in uranium silicide fuels.

Polarized Raman spectroscopy was employed to observe field-induced domain switching in BaTiO3-based multilayer ceramic capacitors (MLCCs). Un-polarized Raman intensities of vibration modes A1(TO2,TO3) are decreased with increasing the external field from 0 MV/m to 5 MV/m, which is caused by the decrease of c-domain volumes. This phenomenon can be visualized from the simulated image gained from the mapping results in cross polarization. It shows that the c-domains are switched to the direction of electric field (3.75 MV/m). We also found that the load to imprint Vickers indentation on the polished MLCCs surface can drive the domains out of the plane parallel to internal electrodes into in-plane textures. Meanwhile, the in-plane domains in the investigated area are switched to form a uniform orientation by the local introduced compressive stress. Due to the existence of cracks, the domains near cracks will re-orient and align with the direction of the relative tensile stress, resulting in a different orientation.

We study the electronic properties of CuAlO2 doped with S by the first principles calculations and find that the band gap of CuAlO2 is reduced after the doping. At the same time, the effective masses are also reduced and the density of states could cross the Fermi level. These results show that the conductivity of CuAlO2 could be enhanced by doping the impurities of S, which needs to be further studied.

A simple method to fabricate silica micro/nano-needle arrays (SNAs) is presented based on tube-etching mechanism. Using silica fibers as templates, highly aligned and free-standing needle arrays are created over large area by simple processes of polymer infiltration, cutting, chemical etching and polymer removal. Their sizes and orientations can be arbitrarily and precisely tuned by simply selecting fiber sizes and the cutting directions, respectively. This technique enables the needle arrays with special morphology to be fabricated in a greatly facile way, thereby offers them the potentials in various applications, such as optic, energy harvesting, sensors, etc. As a demonstration, the super hydrophobic property of PDMS treated SNAs is examined.

A first-principles method is employed to study the mechanism of screening depolarizing field in two-dimensional BaTiO3 nanosheets. The geometric structures and ferroelectric properties show that the low-dimensional BaTiO3 with thickness m = 3 is a freestanding ultrathin film. Therefore, the scale of BaTiO3 nanosheets is defined as m = 1 and 2. The stable domain period corresponding to m = 1, 2, and 3 is 2, 2, and 6, respectively. When m = 1 and 2, only the spontaneous polarizations perpendicular to the surfaces are observed, and they are ∼6 and 15 μC/cm2, respectively. This indicates that the depolarizing field still has an effect on spontaneous polarizations. The difference in macroscopic charge density distribution between ferroelectric and paraelectric phases reveals that a dipole is formed at the ferroelectric domain wall, which leads to a decrease in the depolarizing field in the direction [001]. As a consequence, the critical thickness disappears.

Radio-frequency magnetron sputtering was employed to grow BaTiO3 (BT) films on base metal Ni substrates. The dependence of electrical properties on thickness was investigated in the thickness range from 200 to 1160 nm from dielectric and alternating current (ac) impedance measurements. X-ray diffraction results show that a compressive stress is introduced due to the large difference in thermal expansion coefficients between BT and Ni, and it is reduced with increasing thickness. The capacitance density is reduced with increasing thickness, which is caused by a decrease in residual stress and grain size. Ac impedance spectra demonstrate that the electrical resistance of the BT film is attributed to electrode interfaces, grain boundaries and grains, and it is enhanced with increasing thickness. From impedance spectra analysis, the reduced oxygen vacancies in the vicinity of electrode interfaces and in each grain can be considered to be responsible for the enhanced resistance and reduced dielectric loss of the BT film with increasing thickness.