Coprecipitation synthesis and negative thermal expansion of NbVO5

Abstract

We develop a coprecipitation synthesis route to prepare NbVO(5) with simple oxide Nb(2)O(5) and NH(4)VO(3) as starting materials. No metal alkoxide or organometallic substance was used in the process. Nano-crystal NbVO(5) was obtained by calcination of the coprecipitates at 550 °C for 2 h. DSC/TG and XRD investigations indicate that the target compound NbVO(5) 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 NbVO(5) 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 NbO(6) octahedra and VO(4) tetrahedra in the flexible framework structure. The present synthesis route is facile and easy to be extended to prepare analogues such as TaVO(5), etc.

Two Decades of Negative Thermal Expansion Research: Where Do We Stand?

“…NTE has also been reported in materials with the delafossite structure [152,153,154], A IV 2 O(PO 4 ) 2 (A = Zr, Hf, U, Th) [155,156,157,158,159], ReO 3 [160], NbOPO 4 [161,162,163], NbVO 5 [164], and TaVO 5 [165]. While not an oxide, strong NTE in ScF 3 , which adopts the simple ReO 3 structure, was reported by Greve et al in 2010 [166].…”

Control of Reaction Pathways for Rapid Synthesis of Negative Thermal Expansion Ceramic Zr2P2WO12 with Uniform Microstructure

“…Negative thermal expansion (NTE) materials have received wide attentions due to their potential applications in fine optical, electronic, aviation, and aerospace devices, etc . Zr 2 P 2 WO 12 (ZPW) is one of the interesting materials of A 2 W 3 O 12 family (A is a rare earth or a 3 valence transition metal) by replacing A with a 4 + cation and introducing two P to the W positions to retain the charge balance.…”

A mechanochemical route for the synthesis of VNbO5 and its structural re-investigation using structure solution from powder diffraction data

“…These systems display three endothermic signals, peaked at around 917, 990 and 1001 K. The firsts two peaks occurred at temperatures comparable with those observed in the DSC measurement reported by Wang et al, but with difference in the relative intensities. 13 These signals were ascribable to the formation of V4Nb18O55 and VNb9O25 + V2O5, respectively. The third peak (1001 K) could be related to the further transformation to VNb9O25 and V2O5 and it can be shifted at higher temperature due to the inhomogeneous particles size distribution.…”

“…The occurrence of such exothermic peak confirms that the amorphous substance obtained by extensive ball milling possesses chemical composition and viscosity regimes similar to those obtained after sol-gel and co-precipitation syntheses. 9,13 In these works the thermogram profiles exhibited, in fact, a characteristic crystallization temperature in the range 705 -745 K, which results in the formation of orthorhombic VNbO5.…”

“…12 Further approaches, recently reported in literature, involved sol-gel techniques with the use of organometallic reagents, metal alkoxides and organic precursors or, alternatively, co-precipitation methods. 9,13 However, the expensive and hazardous organometallic salt reagents used as metal sources, together with the formation of undesired by-products, limit significantly the extensive use of these synthesis routes.…”