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<middle dot>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.