Barium borate, also called barium diborate, barium boron oxide, barium metaborate, or (as an optical crystal) BBO (BaB2O4 or Ba(BO2)2) is an inorganic compound, a borate of barium. It is available as a hydrate or dehydrated. Barium borate monohydrate is prepared from the solution of barium sulphide and sodium tetraborate. Barium borate is resistant to moisture and ultraviolet radiation. It can act as UV stabiliser for polyvinyl chloride.