Polymorphs of layered honeycomb oxide Li₂Ni₂TeO₆: Their magnetism and battery cathode properties

Layered transition-metal oxides with the formula A₂M₂TeO₆ (A = alkali or other monovalent cation, M = transition metal) form a versatile family of honeycomb compounds with diverse structural and functional properties. Among them, Li₂Ni₂TeO₆ is notable for its reduced alkali ionic radius compared to related systems, which influences both its stability and functional behavior. In this work, we carried out a structural study of Li₂Ni₂TeO₆ synthesized via solid-state reaction and ion-exchange methods and characterized the resulting phases using powder X-ray diffraction. Rietveld refinements show that the solid-state route produces an orthorhombic Fddd phase with stacking disorder, while the ion-exchange pathway stabilizes a Cmca phase that accommodates both O2 and P3-type stackings. This polymorphism is relevant to functional properties, as layered nickel tellurates are of interest for rechargeable battery applications. Our ongoing studies aim to understand how different space-group symmetries affect the magnetic behavior of Ni²⁺ and to evaluate Li₂Ni₂TeO₆ as a battery cathode material.