niobate

Niobate is a term used for compounds that contain niobium in oxyanion or oxide form, typically in the +5 oxidation state. The most common niobate species are the orthoniobate ion NbO4− and the metaniobate ion Nb2O7^4−, which form salts with alkali and alkaline-earth metals. Examples include potassium metaniobate K2Nb2O7 and sodium metaniobate Na2Nb2O7. Some niobates are solid-state oxides such as KNbO3 and NaNbO3, which are perovskite-related materials rather than simple ionic salts.

In terms of structure, orthoniobate NbO4− features a tetrahedral NbO4 unit, while metaniobate Nb2O7^4− consists of two NbO6 octahedra linked by shared oxygens to form a larger anionic framework. When incorporated into solid compounds, these anionic units build extended three-dimensional frameworks or layered structures, depending on the cation and synthesis conditions.

Synthesis of niobates is typically accomplished by high-temperature solid-state reactions between Nb2O5 and alkali sources such as Na2CO3 or K2CO3, often followed by washing and crystallization. Alternative approaches include hydrothermal, sol-gel, and other solution-based methods to yield crystalline alkali niobates or mixed-metal niobates.

Applications of niobate materials are diverse. Alkali niobates and related oxides are used in ceramics and as electro-optic and ferroelectric materials. KNbO3 is a well-known nonlinear optical crystal, while other niobates are explored as photocatalysts, gas sensors, and precursors for functional nanomaterials. The niobate family is sometimes discussed in relation to tantalates, which share similar structural motifs.