Sodium layer chiral distribution and spin structure of Na2Ni2TeO6 with a Ni honeycomb lattice

Abstract

The nature of Na ion distribution, diffusion path, and the spin structure of P 2-type Na2Ni2TeO6 with a Ni honeycomb network has been explored. The nuclear density distribution of Na ions reveals a 2D chiral pattern within Na layers without breaking the original 3D crystal symmetry, which has been achieved uniquely via an inverse Fourier transform (iFT)-assisted neutron diffraction technique. The Na diffusion pathway described by the calculated iso-surface of Na ion bond valence sum (BVS) map is found consistent to a chiral diffusion mechanism. The Na site occupancy and Ni 2+ spin ordering were examined in detail with the electron density mapping, neutron diffraction, magnetic susceptibility, specific heat, thermal conductivity and transport measurements. Signatures of both strong incommensurate (ICM) and weak commensurate (CM) antiferromagnetic (AFM) spin ordering were identified in the polycrystalline sample studied, and the CM-AFM spin ordering was confirmed by using a single crystal sample through the k-scan in the momentum space corresponding to the AFM peak of ( 1 2 , 0, 1).

Temperature-Dependent Na-Ion Conduction and Its Pathways in the Crystal Structure of the Layered Battery Material Na2Ni2TeO6

“…Ni, Te and O in the crystal structure [Fig. 8(b)] in agreement with the previous reports4,7 . Different Biso values for three crystallographic Na1, Na2, and Na3 sites may be expected, however, a trial refinement with individual Biso values resulted into a divergence.…”

“…One of the major challenges in Na-ion batteries is to design improved materials for better efficiency. In this regard, the family of Na based compounds Na2X2TeO6 (where X = Co, Ni, Zn, Mg, and Fe) has drawn good attention in recent years [4][5][6][7][8] . These compounds are reported to have significant Na conductivity at room temperature, suitable for application in a Na-ion battery 4 .…”

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

“…For instance, Na 2 M 2 TeO 6 (with M being Mg, Zn, Co or Ni) possess P2-type structures, the nomenclature arises from their repetitive two-honeycomb layers sequence in the unit cell with prismatic coordination of Na atoms with oxygen in the interlayer region. 24,34,60,71,173 Structures such as O3-type stackings can be found in Na 3 M 2 SbO 6 (here M = Zn, Ni, Mg or Cu) and Na 3 LiFeTeO 6 , whereas Na 3 Ni 2 SbO 6 and Na 3 Ni 2 BiO 6 reveal O1-type and P3-type stackings during the electrochemical extraction of alkali Na atoms. 58, [80][81][82][83]91,174 Note that the aforementioned oxide compositions are representative of the main stackings observed, and is by no means, an exhaustive summary.…”

Evidence of Unique Stacking and Related Topological Defects in the Honeycomb Layered Oxide: K2Ni2TeO6

“…[8,11,15,16,29,44,49] Figure 1 shows a compendium of the coordination adopted by A alkali atoms in a majority of honeycomb layered oxides reported so far. [5,8,11,15,31,[37][38][39][40][41][42][43][44][45][46][47][48][49][50][51][52][53][54] It is worthy to note that for the formation of prismatic coordination (P-type), interlayer distances wider than octahedrally coordinated (O-type) layered oxides are required. [35] Therefore, honeycomb layered oxides containing alkali atoms with larger ionic radii such as K or Rb typically result in P-type configurations.…”

“…adopted by representative honeycomb layered oxides reported so far. [5,8,11,15,31,[37][38][39][40][41][42][43][44][45][46][47][48][49][50][51][52][53][54] Note here that T, O and P denote the coordination of the alkali atoms (sandwiched between the honeycomb slabs) with the adjacent oxygen atoms of the honeycomb slab. In this case, the letters 'T', 'O' and 'P' denote tetrahedral (highlighted in green), octahedral (in orange) and prismatic (in red) coordination, respectively.…”