Coprecipitation synthesis and negative thermal expansion of NbVO5

Abstract

We develop a coprecipitation synthesis route to prepare NbVO₅ with simple oxide Nb₂O₅ and NH₄VO₃ as starting materials. No metal alkoxide or organometallic substance was used in the process. Nano-crystal NbVO₅ was obtained by calcination of the coprecipitates at 550 °C for 2 h. DSC/TG and XRD investigations indicate that the target compound NbVO₅ is completely formed up to 504.5 °C and is thermally stable below 658 °C. Rietveld XRD refinements give an orthorhombic structure with space group Pnma and lattice parameters, a = 11.8453(2), b = 5.5126(3) and c = 6.9212(2) Å, respectively. In particular, HTXRD determinations show a negative thermal expansion in NbVO₅ with a TEC of −6.63 × 10⁻⁶ °C⁻¹ in the temperature range of RT–600 °C. This fact is ascribed to the tilting of NbO₆ octahedra and VO₄ tetrahedra in the flexible framework structure. The present synthesis route is facile and easy to be extended to prepare analogues such as TaVO₅, etc.