Multiple phase formation in the binary system Nb2O5WO3

A number of high-temperature mixed oxides of niobium and tungsten, containing less than 10 mole percent WO3, have been examined by electron diffraction and microscopy. The unit cell dimensions and symmetries of three new phases found in this region have been determined. The structures proposed for them are based upon the ordered intergrowth of high temperature Nb2O5 and WNb12O33, leading to the ideal compositions WNb26O68, WNb40O103 and WNb68O173. Lattice images of suitably oriented fragments of these materials proved to be particularly useful in elucidating the structural relationships between them. The observations pose a number of questions concerning definitions in solid state chemistry.