Xinggui Long

Defect behavior induced by helium cluster growth in titanium crystals

The growth of helium cluster in titanium crystals is simulated in great detailed approach using molecular dynamics. We observe that, as the helium cluster grows, defects around the cluster are formed and the local pressure increases. However, at certain point in the growth process, the defects are found to rapidly escape as a whole from the helium cluster, accompanied by the relief of local high pressure and the recovery of Ti crystal structure around the helium cluster.

Effects of carbon nanotubes on the dehydrogenation behavior of magnesium hydride at relatively low temperatures

Dehydrogenation in MgH2 was found to lead to a transition from an incubation stage controlled by nucleation to an accelerated stage controlled by the movement of the interface. Addition of carbon nanotubes destabilized Mg–H bonding and reduced the energy barrier for nucleation, which is mainly related to the electron affinity of their curved surface.

Progress of Helium Evolution in Aging Titanium Tritide Film

Abstract Helium release from titanium tritide films at room temperature have been studied. The evolution of lattice defects in long-aged titanium tritide films is also investigated by X-ray diffraction (XRD) over a period of about 1600 days (>4 years). And the thermal desorption (TD) has been used to investigate the 3He release from titanium tritide film with 3He/Ti atom ratio from 0.006 to 0.325. Results of XRD, TD and helium release were synthesized. A continuum-scale evolutionary model of helium for aging titanium tritide film is described which accounts for major features of the tritide experiment data. The combined stress-assisted-block loop punching growth for random bubble arrays and an average ligament stress criterion predicts an onset of inter-bubble fracture in good agreement with the He/Ti ratio observed for rapid He release.

First-principles study of electronic, dynamical and thermodynamic properties of γ-Li4SiO4

We have studied the structural, electronic and dynamic properties of γ-Li4SiO4 (lithium orthosilicate) using density functional theory (DFT) with the generalized gradient approximation (GGA). The crystal structure is fully relaxed. The electronic band structure and Density of States (DOS) calculations indicate that γ-Li4SiO4 is an insulator with an indirect band gap of 5.19 eV and it has a conduction band with the width of 5.92 eV and two valance bands with the width of 4.45 eV and 0.57 eV, respectively. In the partial DOS, Li and Si electronic densities increase more sharply than O atoms. Comparing with previous works, the phonon dispersion curves without negative frequencies are calculated along high symmetry points. By adding the Born effective charges in the phonon calculation, the LO–TO splittings are also calculated which indicate that γ-Li4SiO4 is polar and anisotropic. The optical modes of phonon frequencies at Γ point are assigned as Raman and Infrared-active modes. Additionally, the thermodynamic functions (entropy, internal energy, Helmholtz free energies and constant-volume specific heats) were determined by using the phonon DOS. The calculated results may provide useful guidance of γ-Li4SiO4 for future experimental studies in some degree.

Fabrication processing effects on the microstructure and morphology of erbium film

The effect of substrate temperature on the microstructure and the morphology of erbium film are systematically investigated using X-ray diffraction (XRD) and scanning electron microscopy (SEM). All the erbium films are grown by electron-beam vapor deposition (EBVD). A novel preparation method for observing the cross-section morphology of the erbium film is developed. The films deposited at 200 °C have (002) preferred orientation, and the films deposited at 450 °C have a mixed (100) and (101) texture, due to the different growth mechanisms of surface energy minimization and recrystallization, respectively. The peak positions and the full widths at half maximum (FWHMs) of erbium diffraction lines (100), (002), and (101) shift towards higher angles and decrease with the increasing substrate temperature in a largely uniform manner, respectively. Also, the lattice constants decrease with increasing temperature. The transition in the film stresses can be used to interpret the changes in peak positions, FWHMs, and lattice constants. The stress is compressive for the as-growth films, and is counteracted by the tensile stress formed during the process of temperature cooling to room temperature. The tensile stress mainly originates from the difference in the coefficients of thermal expansion of the substrate-film couple.