Insights into Ni₃TeO₆ calcination via in situ synchrotron X-ray diffraction

The versatility of metal tellurate chemistry enables the creation of unique structures with tailored properties, opening avenues for advancements in a wide range of applications. However, precise nanoengineering of Ni₃TeO₆, a ceramic Ni tellurate with a broad variety of properties, like electrical, magnetic, photocatalytic and multiferroic properties, demands a deep understanding of the synthesis process, which is strongly influenced by experimental parameters. This study delves into the formation mechanism of Ni₃TeO₆ nanoparticles during calcination of hydrothermally produced precursors, using in situ synchrotron X-ray diffraction, complemented by post-mortem TEM and XPS, and thermal analysis. The results reveal a reaction sequence involving dehydration and dehydroxylation of stoichiometric Ni/Te oxyhydroxide coordinated by Te. This oxyhydroxide can be schematically represented by a formula of (3Ni/Te)(OOH)₄·H₂O. Subsequently, preferential nucleation of Ni₃TeO₆ occurs. Further calcination after full crystallization of Ni₃TeO₆ leads to the formation of a different Ni tellurate (NiTeO₄) phase as an impurity. These findings clarify the reactions occurring during calcination of Ni/Te mixed precursors, which have frequently been inferred from empirical and post-mortem reports but not confirmed via comprehensive and in situ guided explorations.