Recent Research Highlights

Niobium tungsten oxides are currently probed as promising candidates for applications as electrochemical and thermoelectric materials. The manifold structural chemistry in the pseudo-binary system Nb₂O₅/WO₃, however, has puzzled solid state chemists and crystallographers since the early 1960s. Based on the ReO₃ type with corner-sharing octahedra MO₃ (M = Nb,W), various octahedral frameworks cover oxygen:metal ratios in the range 2.5 = O/ΣM = 3.0, i.e. from Nb₂O₅ (left) to WO₃ (right, see scheme). The review begins with an overview about synthesis and structures of the existing phases comprising structures of the block-type and related to the tetragonal tungsten bronzes. Derivatives of a certain phase can be prepared by the substitution of Nb⁵⁺ according to Nb⁵⁺ = M⁴⁺ + W⁶⁺ leading to isostructural solid solution series. Aspects of the structural characterization by X-ray diffraction and by various electron microscopy methods are discussed before the listing of physical properties and potential applications closes this overview.

The Complex Crystal Chemistry of Niobium Tungsten Oxides
F. Krumeich, Chem. Mater. 2022, 34, 911-934  DOI