Chaoying Wang

Multi-scale simulation of lithium diffusion in the presence of a 30° partial dislocation and stacking fault in Si

The multi-scale simulation method is employed to investigate how defects affect the performances of Li-ion batteries (LIBs). The stable positions, binding energies and dynamics properties of Li impurity in Si with a 30° partial dislocation and stacking fault (SF) have been studied in comparison with the ideal crystal. It is found that the most table position is the tetrahedral (Td) site and the diffusion barrier is 0.63 eV in bulk Si. In the 30° partial dislocation core and SF region, the most stable positions are at the centers of the octagons (Oct-A and Oct-B) and pentahedron (site S), respectively. In addition, Li dopant may tend to congregate in these defects. The motion of Li along the dislocation core are carried out by the transport among the Oct-A (Oct-B) sites with the barrier of 1.93 eV (1.12 eV). In the SF region, the diffusion barrier of Li is 0.91 eV. These two types of defects may retard the fast migration of Li dopant that is finally trapped by them. Thus, the presence of the 30° partial di...

Phase stability, electronic structure and optical properties of BiInO3 under strain

We use density functional calculations to elucidate the effects of compressive and tensile strain on the structural, ferroelectric, electronic, and optical properties of BiInO3. Compared to tensile strain, compressive strain results in larger changes to the related physical properties of BiInO3. At a compressive strain about 6.3%, BiInO3 undergoes a first-order phase transition from ferroelectric state to paraelectric state. In the case of tensile strain, BiInO3 can retain its ferroelectricity, and while in its ferroelectric state, become unstable. The ferroelectric polarization and band gap of BiInO3 can be tuned by strain. The optical dielectric function under strain was also investigated. Based on the calculated energy band structures, the transitions peaks of dielectric function are discussed in detail. The change of energy band structures also indicated that the first-order phase transition in BiInO3 occurs under compressive strain. Our results suggest that BiInO3 should be one of the most promising candidates for replacing the widely used ferroelectric and piezoelectric material PbTiO3, and solve the environmental issues associated with the toxicity of lead.

Multi-scale simulation of the stability and diffusion of lithium in the presence of a 90° partial dislocation in silicon

The stable positions, binding energies, and dynamic properties of Li impurity in the presence of a 90° partial dislocation in Si have been studied by using the multi-scale simulation method. The corresponding results are compared with the defect-free Si crystal in order to reflect how the dislocation defect affects the performances of Li-ion batteries (LIBs) at the atomic level. It is found that the inserted Li atom in the dislocation core and nearest regions is more stable, since the binding energies are 0.13 eV to 0.52 eV larger than the bulk Si. Moreover, it is easier for Li atom to diffuse into those defect areas and harder to diffuse out. Thus, Li dopant may tend to congregate in the dislocation core and nearest regions. On the other side, the 90° partial dislocation can glide in the {111} plane accompanied by the diffusion of Li impurity along the pentagon ring of core. In addition, the spacious heptagon ring of dislocation core can lower the migration barrier of Li atom from 0.63 eV to 0.34 eV, whi...

Strain-induced improvements on piezoelectric and nonlinear optical properties of BiAlO3

Using density functional theory, we calculate the effect of compressive and tensile strain on the electronic, piezoelectric, and nonlinear optical properties of BiAlO3. Our results show that applying strain effectively reduces the band gap of BiAlO3. Analysis of the piezoelectric constant shows that the tensile strain can significantly enhance the piezoelectricity of BiAlO3, while the change in the second harmonic generation (SHG) tensor under applied strain indicates that the nonlinear optical properties of BiAlO3 can also be effectively modulated by applying strain. Moreover, the SHG tensors d 12 and d 31 of strain-free BiAlO3 are even higher than that of LiNbO3. The noncentrosymmetric distortion of BiAlO3 resulting from its BiO12 cuboctahedron structure is the reason for its excellent SHG properties. However, compressive strain changes the main source of SHG from the BiO12 cuboctahedron to the AlO6 octahedron.

DIFFUSION OF LITHIUM IN SILICON AFFECTED BY 60° MISFIT-DISLOCATION

In this paper, the diffusion dynamics of Li atom in bulk Si with misfit (60°) dislocation has been investigated with the multi-scale simulation method. The results demonstrate that the dislocation core may confine the Li atom diffusion along the dislocation line, with its much larger binding energy and relatively smaller diffusion barrier compared to that in bulk Si. The reconstructions occurred in the dislocation core may open a low barrier route for the Li atoms entering into the core.

Strong increase in superconducting Tc for Nb2InC under compressive strain

Using first-principles, we investigate strain effects on the phonon spectrum, heat capacity CV, Debye temperature θD, and electron-phonon coupling of Nb2InC. It finds that its heat capacity increases and Debye temperature decreases as strain increases. Analysis of the phonon spectrum and Eliashberg spectral function shows that the superconductivity of Nb2InC mainly originates from C vibrations parallel to and Nb vibrations perpendicular to the Nb2InC layers. A significant enhancement of the superconducting transition temperature Tc up to 25.98 K is observed at η = −10% due to an increase of In atomic vibrations under strain. These results provide a means of tuning the superconducting properties of Nb2InC.