Temperature induced twinning in aragonite: transmission electron microscopy experiments and ab initio calculations

The microstructure of aragonite, one of the main bio-mineral and component of bio-inspired materials, was described in numerous investigations. Using transmission electron microscopy (TEM), for the first time we show the effect of temperature on aragonite microstructure. The local increase of (0.5 0.5 0) reflections intensities and appearance of satellite reflections in [11̅0] zone axis were observed above 350°C. We explain the appearance of satellite reflections by the generation and ordering of {110} twin boundaries and suggest new thermal mechanism of the twin boundaries generation. We check the viability of this mechanism by ab initio molecular dynamics (AIMD) simulations and generalized solid state nudge elastic band (g-SSNEB) calculations.

DFT Study on the Li Mobility in Li-Ion-Based Solid-State Electrolytes

ABSTRACTWe have investigated the diffusion mechanisms of Li-ion in amorphous lithium phosphite (LiPO3) with the addition of sulphur. By applying the nudge elastic band (NEB)1 method in crystal LiPO3 and Li3PO4, we have confirmed the ease in diffusion pathways for Li ions in LiPO3 which is quite consistent with the previous theoretical finding. From our diffusion study in 0.5 Li2O- 0.5 P2O5 and 0.4 Li2SO4 –0.6 (Li2O-P2O5) melts above 3000K investigated with ab-initio molecular dynamics (AIMD) has been confirmed by experiments at lower temperatures, we have demonstrated the benefit of S addition in increasing the Li+ mobility. We have also found that the Li2SO4 addition into the glass result in a characteristic shift in Li-ion vibration to a lower vibrational frequency. In addition, the presence of oxygen surrounding the diffusion pathways appears to be essential in assisting the Li+ mobility in both crystalline and amorphous structures.

Structural Shifting and Electronic Properties of Stone-Wales Defect in Armchair Edge (5,5) Carbon Nanotube

Stone Wales (SW) defect is one type of topological defect on the CNT, in this study we performed first principles calculations of SW defects in armchair edge (5,5) carbon nanotube (CNT) by the density functional theory (DFT). Two different defects were studied such as longitudinal and circumference types. Our calculation results show that a longitudinal SW defect is more stable than circumference SW defect. However barrier energy as parameter to control the SW defect in CNT was studied, in calculation we applied Nudge Elastic Band (NEB) method to find minimum energy path (MEP) and barrier energy for SW defect transitions. The result shows that barrier energy of circumference SW defect is lower than another one. We also found that in the case of circumference SW defect, armchair edge (5,5) CNT become semiconductor with the band gap of 0.0544 eV.