Powders of various sizes from a few tens nanometers to a few tens micrometers can be obtained by the careful control of the preparation conditions. The particle shape can also be controlled. The size and shape of particles changes in the course of the stages of particle formation. In the reaction stage, two types of particles can be obtained. When the product particles are formed by the solution-precipitation and solution-diffusion processes, the particles have a growth form and a shape similar to that of one of the reactant particles, respectively. The dominant process is determined by the relative dissolution rate of the reactant particles into the molten salt, and the dissolution rate is determined by the solubility and particle size of the reactant. In the particle-growth stage, the particle size is increased and the particle shape approaches the equilibrium form. For the materials with low crystallographic symmetry, anisometric particles can be obtained. When anisometric particles are desired for materials with high symmetry, the topochemical micro-crystalline conversion can be applied.