Abstract
AbstractTriniobium hydroxide heptaoxide, Nb3O7(OH), was prepared hydrothermally by treating niobic acid or triniobium chloride heptaoxide with 3.0 mol/dm3 sulfuric acid at 250–350°C and 15 MPa. The hydroxide oxide was isomorphous with the low‐pressure form of triniobium fluoride heptaoxide which is built up of 3 X ∞ blocks of the ReO3 structure with crystallographic shear in one dimension. When heated in air, Nb3O7(OH) dehydrated up to 460°C to give poorly crystallized Nb2O5, which, on further heating, changed slowly into a less ordered precursor of MNb2O5(1). Hydrothermal treatment of Nb3O7(OH) with pure water at 400–500°C afforded P and RNb2O5; the conversion of Nb3O7(OH) is explained in terms of the close structural relation among these three forms.
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