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.