Nonhexagonal Na Sublattice Reconstruction in the Super-Ionic Conductor Na₂Zn₂TeO₆: Insights from Ab Initio Molecular Dynamics

Abstract

In this work, we examine the distribution of Na+ ions in the interlayer of the super-ionic conductor Na2Zn2TeO6 by means of atomistic first-principle modeling based on density functional theory. This layered structure presents a variety of partially occupied interstitial Na sites forming a triangular prismatic coordination group with the neighboring O atoms. We examine the energetics of Na periodic arrangements, considering distinct occupation patterns of these interstitial sites. We then simulate high-temperature annealing of the system by means of ab initio molecular dynamics simulations, finding that the Na sublattice prefers a disordered distributions along the available interstitial sites rather than a honeycomb arrangement conformal to the periodicity of the Zn–Te layers. Suitable supercells are constructed, reproducing the arrangement patterns observed in the most favorable configurations obtained by simulated annealing. We report a structure with rhomboidal reconstruction of the Na sublattice as the most energetically favorable, and note that the associated occupation of the interstitial sites is compatible with experimental data. We also report the tendency for the formation of a pentagon–triangle reconstruction, predicted to become increasingly favorable as the system is compressed.

Honeycomb layered oxides: structure, energy storage, transport, topology and relevant insights

“…9. 15,59,90,173,[249][250][251][252][253][254][255]257,258 Experimentally, the measurement of ionic conductivity is conducted via linear response techniques with polarised electromagnetic fields such as electrochemical impedance spectroscopy (EIS). 259 EIS entails applying a low amplitude low frequency oscillating Fig.…”

“…9 Solid-state diffusive properties of typical cations sandwiched between honeycomb slabs of various layered oxides showing values of ionic conductivity attained in honeycomb layered oxides at room temperature and also at high temperature (300 1C). 59,90,173,[249][250][251][252][253][254][255] Honeycomb layered oxides based on tellurates generally tend to show high ionic conduction, owing to the partial occupancy of alkali atoms in distinct crystallographic sites that facilitate rapid hopping diffusion mechanism. Inset shows the plot of the dependency of (normalised) conductance s to (normalised) thermal energy k B T of the cations determined by linear response of the diffusion current to low amplitude, slowly oscillating voltage by electrochemical impedance spectroscopy (EIS).…”

“…412 Experimental and theoretical reports on the structures of these materials has already revealed some stacking disorders with honeycomb layered species such as Na 3 Ni 2 SbO 6 , Na 2 Zn 2 TeO 6 and Na 2 Ni 2 TeO 6 , associating them with emergent functionalities such as phase transitions, magnetic ground states and ionic diffusion. 60,170,253,413 Although defects have been known to have both prolific and detrimental effects on honeycomb layered oxides, they still remain vastly underexplored. Nonetheless, de novo computational and experimental techniques are expected to uncover new defect physics and chemistry that will expand their uses into multiple fields.…”

Unveiling Structural Disorders in Honeycomb Layered Oxide: Na2Ni2TeO6

“…In this context, theoretical and experimental studies to investigate the structural disorders particularly on the aforementioned O-type and P-type Na honeycomb layered oxides have been commissioned in an attempt to draw correlations between the atomic structure (microscopic details) with macroscopic manifestations such as electrochemical performance and phase transitions. [44][45][46] Recent studies utilising TEM on the O3-type Na3Ni2SbO6 have revealed the existence of disordered sequences in the arrangement of Ni and Sb atoms as a possible reason behind phase transitions and improved ion mobility. [44] Even though, P-type Na2M2TeO6 would make an ideal platform for investigating structural revolutions on pristine cathodes, crystallography studies on these materials lack rigour with literature limited only to theoretical computations and XRD analyses conducted on Na2M2TeO6.…”

“…[44] Even though, P-type Na2M2TeO6 would make an ideal platform for investigating structural revolutions on pristine cathodes, crystallography studies on these materials lack rigour with literature limited only to theoretical computations and XRD analyses conducted on Na2M2TeO6. [45][46][47] As such, information pertaining the local atomistic structures (TEM) and emergent attributes remain elusive.…”