Hydrothermal synthesis is a method used to create materials, particularly crystals, by using high temperature and pressure in a water-based solution. This process occurs in a sealed container, known as an autoclave, where water acts as a solvent. The conditions allow for the dissolution of reactants and promote the growth of desired products, often resulting in high-quality crystals. This technique is commonly employed in the production of zeolites, nanomaterials, and various ceramics. It is favored for its ability to produce materials with specific properties and structures that are difficult to achieve through other synthesis methods.