Computer simulation of ionic transport in silver iodide within carbon nanotubes

Structure and Ionic Transport Properties of AgI1–xBrx within Single-Wall Carbon Nanotubes from Molecular Dynamics Simulation

“…Additionally, in ref , TEM images for some AgI samples in CNTs with diameters between 15 and 17 Å were demonstrated that the authors attributed to asymmetric sphalerite-like γ-AgI nanowire fragments (and the phase diagram presented in the Supporting Information for ref suggested that in any CNT wider than 13 Å, sphalerite-like morphologies are basically possible). Those sphalerite-like structures show a periodicity along the tube with the period 4.55–4.7 Å, close to the value obtained for model AgI INTs within CNTs in our previous simulations and in the present work (approximately 4.9 Å). However, the ion arrangement in the fragments of γ-AgI is also quite different from a rolled-net nanotube.…”

“…One can suppose that higher ion mobility and lower activation energies in the latter as compared to the former are caused by some modification of the potential landscape that occurs when additional ions are placed in the tube center, without changing the general pattern of ionic motion in the superionic nanocrystalline aggregate as it was obtained from the simulations of AgI@SWNT (silver ions jumping between lattice sites, with a lot of defects in the lattice, high cooperativity, and significant local structure perturbations associated with the jumps). The “intermediate” values of E a given above also suggest that, while summary characteristics of cation disorder and mobility in the simulated superionic AgI 1– x Br x @SWNT are liquidlike (high values of Δ and D ), the ion binding in these systems is stronger than in “classical” superionics with a fully disordered sublattice, and the ionic motion can still be described in terms of lattice sites and jumps between them through formation and migration of Frenkel defectsin the same way as in “nanograined” AgI at temperatures corresponding to the diffuse superionic transition, but with relatively weakly bound ions (lower defect formation and migration activation energies than in pretransition β- or γ-AgI nanograins studied in ref ).…”

“…62,63 The simulations are performed using the DL_POLY software package, 64 following the same procedure and with the same basic parameters as in our previous works. 60,61 At the preliminary stage, the bulk phase of AgI 1−x Br x above the melting point is simulated, with standard periodic boundary conditions (PBC) imposed on the system and Ewald summation used for calculating the electrostatic energy. Then, filling of carbon SWNTs by AgI 1−x Br x is modeled: in the center of the MD cell representing equilibrated AgI 1−x Br x melt, a hole is created by removing an equal number of cations and anions, a carbon SWNT is placed in the hole, and the temperature T of the system is decreased to 500 K at zero pressure, either abruptly before filling (so that the tube is filled at the same time as the melt freezes) or after 300 ps of filling at 1000 K (in this case, the freezing occurs only after molten AgI 1−x Br x has already entered the tube).…”

Rock-salt and helix structures of silver iodides under ambient conditions

“…The rock-salt phase of silver iodides inside MWCNTs with inner diameters about 4–8 nm was further confirmed by the simulation results using a MD method [ 35 ], where a Parrinello–Rahman–Vashishta (PRV) model [ 36 ] was employed to describe the energies between the silver and iodine ions, the Lennard–Jones (LJ) potential [ 37 ] was employed to describe the energies between the carbon atoms and silver or iodine ions, and the Tersoff potential [ 38 ] was employed to describe the energies between carbon atoms within the carbon nanotubes. A rock-salt phase was obtained for silver iodides encapsulated inside carbon nanotubes with inner diameters of 5.4 nm after annealing and relaxing dynamics, as shown in Fig.…”

Stabilization of metastable structures from high pressure or high temperature to ambient conditions

“…The other is a helix structure of silver iodide in single-walled carbon nanotubes (SWCNTs) with inner diameters of about 1.4 nm. Three outer iodine radial arms and three inner silver radial arms construct this particular structure, instead of the previously predicted single-walled inorganic nanotubes [ 4 ]. This new structure, which has not been recorded on the phase diagram, was simulated as stable with the Vienna Ab-initio Simulation Package (VASP), and needs deep investigation into its properties and potential applications.…”