Factors Governing MgO(111) Faceting in the Thermal Decomposition of Oxide Precursors

Abstract

The preparation of metal oxide particles, such as MgO, NiO, and ZnO, exposing polar facets via the decomposition of suitable precursors in air, molten salts, ionic liquids, or other media has been reported; however, the main driving force(s) and factors that determine their morphology have largely remained elusive. For instance, the adsorption of ions within a molten medium on a growing oxide surface has been proposed to stabilize MgO{111} facets by the so-called molten salt route (MSR). In this article, we examine the thermal decomposition of MgO precursors to assess the influence of precursor decomposition pathways, including the physical state of the reaction intermediates and the possibility of dissolution–recrystallization processes in the formation of octahedral MgO particles. We found that solid-to-solid conversions and recrystallizations in molten nitrates or chlorides are usually incapable of producing well-defined MgO{111} facets, indicating that ion adsorption on MgO may not be the main morphol...