Solid-state synthesis, or the ceramic method, is commonly used to cause a chemical reaction from solid starting materials to form a new solid with a well-defined structure. End products include polycrystalline materials, single crystals, glasses, and thin-film materials that are widely used for energy and electronic applications.
Fine-grain metal compounds are combined, pelletized, and heated at a controlled temperature for a specific time period. Some metal compounds, such as metal oxides or salts, require extreme conditions, such as high temperatures and pressure, to initiate reactions in a molten flux or a rapidly condensing vapor phase. This process is often referred to as “shake and bake” or “heat and beat” chemistry.
The reaction rate in solid state synthesis is particularly important to characterize. Solid state reactions must go to completion, as techniques for purification of formed solids are severely limited. The rate of the solid-state reaction depends on the reaction conditions, including the structural properties, shape and surface area of the reactants, the diffusion rate, and the thermodynamic properties associated with the nucleation/reaction. The chemical and physical properties of the final materials are determined by the chemical precursors and preparation techniques.
Modern preparation techniques for solid state are not limited to variations on the ceramic method. In solid state metathesis, reactions of metal compounds are initiated by an energy source (e.g., flame, ball mill) and propagated by the heat released during the formation of products and byproducts. Sol-gel methods utilize a concentrated or colloidal solution (the ‘sol’), which is sequentially heated, dried, and aged to form gels, coatings, and nanomaterials. Solvothermal methods involve heating solutions in a pressurized, closed vessel at temperatures above the standard boiling point of the chosen organic solvent; if the solvent is water, this is called the hydrothermal method. Many synthetic methods where a solid material is formed, such as vapor-phase depositions, intercalation, single crystal growth, and nanomaterial syntheses, can be classified as solid state synthesis.