Synthetic methodology and characterization often go hand in hand in the sense that not one but a series of reaction mixtures are prepared and subjected to heat treatment. Stoichiometry, a numerical relationship between the quantities of reactant and product, is typically varied systematically. It is important to find which stoichiometries will lead to new solid compounds or solid solutions between known ones. A prime method to characterize the reaction products is powder diffraction because many solid-state reactions will produce polycrystalline molds or powders. Powder diffraction aids in the identification of known phases in the mixture. If a pattern is found that is not known in the diffraction data libraries, an attempt can be made to index the pattern. The characterization of a material's properties is typically easier for a product with crystalline structures.