Spectroscopic analysis of Na2Ni2TeO6 and Na2(Ni2−xGax)TeO6 (x = 0 to 0.25) honeycomb compounds

Modern technology demands the continuous development of cost-effective functional devices based on low-dimensional quantum materials. Although theoretical predictions provide the best estimates of stacking order and stoichiometric composition, experimentally controlling superstructure fabrication and understanding the resulting complex outcomes remain challenges that ultimately affect device yield and performance. This work presents experimental spectroscopic investigations of Na 2 Ni 2 TeO 6 and of Na 2 (Ni 2−x Ga x )TeO 6 for x ranging from 0 to 0.25 as new cathode materials for all-solid-state sodium batteries. Such analysis is scarce in the literature for sodium nickel tellurite oxides. The proposed gallium incorporation has been predicted to enhance sodium electrical conductivity in the parent honeycomb compound. Complementary structural evaluations by X-ray diffraction and Rietveld analysis validate the phase purity and stoichiometry of the compounds, and confirm a slight expansion of the unit cell when gallium substitutes for nickel. The spectroscopic Raman and infrared (IR) absorption results, in addition to showing the dominance of vibrational lines from tellurium and nickel oxides, reveal detailed structural changes with gallium incorporation at nickel sites, as well as in the frameworks of these ordered growth sequences. The absence of magnon vibration in the IR spectra indicates that incorporating non-magnetic gallium modifies the short-range magnetic properties of Na 2 Ni 2 TeO 6 . Furthermore, high gallium amounts exceeding x = 0.20 induce the formation of the compound oxyhydroxide and oxide polymorphs. This spectroscopic analysis enables faster, easier, and more accurate identification of size-dependent structural modifications at the molecular level, providing insightful information for future device development.