In chemistry, molybdenum bronze is a generic name for certain mixed oxides of molybdenum with the generic formula  where A may be hydrogen, an alkali metal cation (such as Li, Na, K), and Tl.  These compounds form deeply coloured plate-like crystals with a metallic sheen, hence their name.  These bronzes derive their metallic character from partially occupied 4d bands. The oxidation states in KMoO are K, O, and Mo.  MoO is an insulator, with an unfilled 4d band.
These compounds have been much studied since the 1980s due to their markedly anisotropic electrical properties, reflecting their layered structure.  The electrical resistivity can vary considerably depending on the direction, in some cases by 200:1 or more.  They are generally non-stoichiometric compounds.  Some are metals and some are semiconductors.