3. Morphology of powders
3.1. EQUILIBRIUM AND GROWTH FORMS
Powders with grains of various shapes are obtained by molten salt synthesis, depending on the chemical composition and reaction conditions. The presence of a liquid phase promotes the facet formation as usually observed in the single-crystal growth from solution (Elwell & Scheel, 1975). Because the crystal structure determines the crystallographic faces (hkl) of the stable facets, the particle shape is to some extent determined by the chemical composition. Powder particles are formed in two stages in molten salt synthesis. They are the reaction and particle-growth stages, and the supersaturation is high during the reaction stage and almost zero during the particle-growth stage (see 2.2). Because the degree of supersaturation determines the growth rate of each crystallographic face, the particle shape is determined by the reaction conditions, such as the chemical species of the salt used, the reaction temperature and its duration, and the powder characteristics of the reactants.