TRIPOTASSIUM NIONIUM OXIDE SILICATE K3NB3 O6SI2O7

Single crystals of tripotassium niobium oxide silicate, K3Nb3O6Si2O7, have been obtained by slow cooling from a melt. This compound crystall izes in the hexagonal system with space group P $($) over bar$$ 62c. T he framework, built up from Si2O7 ditetrahedra and a group of three co mer-linked NbO6 octahedra, is isotypic with that of Ba3NB6O12(Si2O7)(2 ). The filling of tunnels by K+ (or Ba2+) cations determines the space group to be P $($) over bar$$ 62c (or P $($) over bar$$ 62m).