Ammonium Paratungstate as Doping Source to Enhance Phase Transition Powder

Vanadium dioxide (VO2) is a reversible first-order metal-insulator transition (MIT) at a critical temperature (Tc). It is generally believed that VO2 is a monoclinic structure (M), and presents semiconductive and relatively infrared transparent below Tc, whereas it transforms into tetragonal structure (R), and presents metallic and infrared reflection above Tc. These features make the VO2 suitable for the applications in intelligent energy windows coating, optical switching devices, optical data storage medium, electrodes for electrochromics, lithium batteries and supercapacitors, etc. Nevertheless, the high critical transition temperature of VO2 material (about 68 °C) limits its application.

VO2 doping with W (tungsten) is an efficacious way to overcome this disadvantage. a simple carbothermal reduction method has been presented by the simple direct mixture and calcination to prepare W-doped VO2 controllable phase transition powders, using ammonium paratungstate (APT) as the doping resource.

The experimental procedures are as follows: V2O5 (1–10 μm, purify >99%) were used as precursor, APT (purify >99%) as doping source, and C powders (<1 μm, purify >99%) as reducing agent, respectively. Firstly, amounts of APT, and C have been mixed by planetary milling with agate ball media for 6 h, in which the molar ratio of V2O5 to C for all samples was 2:1 and the molar ratios of APT were shown in Table 1. Secondly, the mixture were poured into a quartz crucible, and then the quartz crucibles have been transferred into the vacuum furnace with N2 protective atmosphere. The V1-xWxO2(x = 0, 0.01, 0.02, 0.03, 0.04, and 0.05) solid solution powders have been obtained after annealing at 850 °C for 2 h.

In conclusion, Tungsten doped vanadium dioxide phase transition powders have been produced using ammonium paratungstate as the doping resource, the method is a simple, high efficiency and low-cost approach. Results showed that the prepared pure VO2 was a monoclinic structure and the W-doped VO2 was a tetragonal structure. The phase transition temperature of VO2 decreased gradually with increasing W-doping content. Tc of VO2 decreased gradually with increasing W-doping content by about 24 °C per W at%. Therefore, the carbothermal reduction method is a simple, high efficiency and low-cost approach to synthesize VO2.

• < Prev
• Next >