Solid State Methods, Hydrothermal

The term ‘‘hydrothermal synthesis’’ is conventionally applied to heterogeneous reactions in aqueous media at temperatures above 100 °C and under autogenous pressures. The method mimics natural conditions for the formation of structurally complex mineral species under relatively mild conditions.¹ Consequently, the technique has been recognized for some time as offering convenient approaches to metastable compounds, low-temperature phases, and materials with elements in unusual oxidation states. Hydrothermal methods have been applied to the preparation of a variety of materials, including microporous phases, chemical sensors, conducting solids, ceramics, magnetic solids, and phosphors.² The applications of hydrothermal methods to crystallization processes,³ zeolite synthesis,⁴ the preparation of metastable oxide materials,⁵ and general preparative chemistry^1,6 have been reviewed.