Systematic study on bulk properties, defect chemistry and Li-ion transport mechanisms of a Li3OCl fast-ion conductor.

The present work uses the ab initio molecular dynamics (AIMD) methodology to simulate ionic transport in amorphous and crystalline Na 2 Si 2 O 5 from 573 to 973 K. The results suggest that amorphous Na 2 Si 2 O 5 is primarily a Na + conductor with negligible O 2À and Si 4+ contributions to ionic conduction, whereas crystalline Na 2 Si 2 O 5 is virtually an electrical insulator. The favorable pathway for Na + transport in amorphous Na 2 Si 2 O is along the two-dimensional channels formed by the SiO 4 tetrahedral layers. The disrupted Na-O coulombic attraction by the long-range disorder in amorphous Na 2 Si 2 O 5 contributes to the enhanced Na + conduction.

The low-lying candidates of hydrated calcium ion clusters, [Ca(H(2)O)(n)](2+) with n = 1-20 and 27, have been extensively sought by using density functional theory (DFT) at BLYP/6-311+G(d,p) level. The results showed that the first hydration shell around the calcium ion was fully occupied by six water molecules, whereas the second hydration shell might be fully occupied with different numbers of water molecules. This just corresponds to different growth patterns of the hydrated calcium ion clusters. Furthermore, we revealed that the vibration entropy contributed to the free energy of an isomer significantly. As a result, the stability of some low-lying candidates at zero-temperature was not maintained at finite temperatures. Therefore, we suggested that, at finite temperatures, the realistic products of [Ca(H(2)O)(n)](2+) should be a mixture of the best candidate and some of metastable isomers for a given cluster size. For a cluster having second and/or third shell of water molecules, we found structural transitions between a low-lying structure and the lowest-energy structure undergoing much lower energy barriers. In addition, the IR spectra of the best candidates were predicted, in which the evolution of hydrogen-bond configurations with the cluster size was revealed.