Structural and transport properties for the superionic conductors AgI and RbAg 4 I 5 through molecular dynamic simulatio
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ORIGINAL PAPER
Structural and transport properties for the superionic conductors AgI and RbAg4 I5 through molecular dynamic simulation ˜ Lara D.2,3 · Garc´ıa Muriel Alvaro1 E. I. Vivas1 · Pena Received: 16 May 2020 / Revised: 16 October 2020 / Accepted: 21 October 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract AgI and RbAg4 I5 are the typical superionic conductors. In this work, molecular dynamics (MD) simulations were performed to obtain their structural (radial and pair distribution function) and dynamic transport properties (mean square displacements, MSD). For AgI, with bcc structure, a pairwise potential based on Coulomb–Buckingham potential, NVE (increasing T ), NP T (decreasing T ) ensembles, MD steps (MDS) of 0.175 × 105 , and the LAMMPS package were used. The temperature was increased 100 K above the melting temperature and when decreased. The MSD as a function of time of Ag-ions and I-ions shows the same behavior. For RbAg4 I5 , P41 32 as space group, a new interatomic potential, NVE ensemble, MDS = 105 , and the Moldy package at room temperature were used. The MSD of Rb-ions and I-ions shows a liquid-like behavior, and the Ag-ions are the highest mobility. Better results for the PDF and MSD were achieved, which is in good agreement with experimental data. Keywords Ag+ conductors · Modeling · Crystal structures
Introduction AgI and RbAg4 I5 are superionic conductors exhibiting high ionic conductivity, σAgI = 2.62 S/cm at T > Tt = 420 K [1] and σRbAg4 I5 = 0.21 S/cm at room temperature (RT) [2]. These superionic conductors show good potential in fuel cells and electrolyzers, electrochemical devices, supercapacitors, power device, and miniaturized sensors, among others [3–7]. From a structural point of view, the transition from β/γ AgI to α-AgI occurs at the transition temperature Tt . The Pe˜na Lara D.
[email protected] E. I. Vivas [email protected] Alvaro Garc´ıa Muriel alvaro [email protected] 1
Departamento de F´ısica, Universidad de Cartagena, SUE Caribe, Bolivar, Colombia
2
Departamento de F´ısica, Universidad del Valle, Cali, Colombia
3
Centro de Excelencia en Nuevos Materiales (CENM), Universidad del Valle, Cali, Colombia
α-AgI phase or high-temperature phase forms a bodycentered cubic structure and the unit cell containing one silver and one iodide ion. RbAg4 I5 undergoes a phase transition at critical temperature Tc = 209 K [8] from β/γ RbAg4 I5 to α-RbAg4 I5 . The unit cell of α-RbAg4 I5 contains 4 rubidium, 16 silver, and 20 iodide ions, with a lattice ˚ and space group P41 32 [9, 10]. parameter a = 11.15 A Many theoretical approaches to explain the superionic conductivity or the phase transition to the high-temperature phase have been proposed: the path probability method [11], cluster formation, and strong mobile–ion interaction within the clusters [12], through concerted migrations of multiple ions with low-energy barriers [13]. For a deeper understanding of this phase transition, it is customary to take a microscopic perspect
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