Study On Preparation And Properties Of M_xWO₃ Tungsten Bronzes

Tungsten bronze, which possessed rich electric transport properties and crystal structure, was widely applied in new generation battery, light-electric sensor and ions-sensitive electrode, etc. Recently, tungsten bronzes doped with alkali metal ions exhibited NIR （Near-Infrared Ray） shielding ability due to the effects of LSPR （Localized Surface Plasmon Resonance）, interface transition and small polaron. The tungsten bronzes doped with alkalis ions were potentially applied as heat insulating film.This paper aimed at synthesis of sodium tungsten bronze and flourine doped cesium tungsten bronze by a convenient and safe method and further improving the NIR shielding ability. The influences of raw materials, capping agent and annealing condition on the microstructure and performance were investigated. The microstructure and properties of tungsten bronzes were characterized by XRD, SEM, TEM, XPS and laser particle sizer analysis, while the NIR shielding ability of samples were determined by UV-Vis spectrometer and Vis-NIR spectrometer. Heat insulation ability of as-prepared tungsten bronzes were measured by self-made testing instrument.It was found, using Na₂CO₃, H₂WO₄ as raw material and oxalic acid or citric acid as capping agent, tungsten bronze or tungstates doped with sodium ions could not be gained directly by hydrothermal method. Using sodium tungstate Na₂WO₄ as raw material, Na0.17W03.085（H₂O）0.17 were obtained by hydrothermal reaction with citric acid. After annealing at 500 ℃ under N₂ atmosphere, Na0.17W0₃.08s（H₂O）0.17 was transformed to hexagonal ammonium tungsten bronze; while tetragonal sodium tungsten bronze Na0.1WO₃ was obtained after annealing at 700℃ and exhibited NIR shielding ability.Fluorine doped cesium tungsten bronze CsxWO₃-yFy was successfully prepared by hydrothermal method with hydrofluoric acid or sodium fluoride, of which addition of sodium fluoride could not raise over F=0.28 otherwise no precipitate would be found. Comparing with the undoped CsxWO₃ sample, F doped CsxWO₃ samples achieved higher visible transparency and NIR shielding ability. However, excessive HF acid addition resulted in the decrease of NIR shielding ability. The as-prepared CsxWO₃-yFy sample with F=0.45 showed the best transparent insulating ability, of which visible light transmittance and NIR shielding rate could reach 48% and 90% respectively. The properties of CsxWO₃-yFy could be further improved by annealing at suitable temperature for suitable time, of which the optimal annealing temperature and time are 500℃ and 30 mins, respectively.