| VO2 is a typical thermochromic compound, the phase transition temperature is 68℃, With the increase of temperature, it has metal-to-semiconductor transition at 68℃. And its physical properties change, too. For example, electrical resistance has 4-5 magnitude abrupt changes, accompanied by abrupt changes in magnetic susceptibility, optical index of refraction transmissivity, and reflectivity and it has infrared screen function. The most important is that phase-transition temperature (Tc) of VO2 powders can be gone down to room temperature by doping. So VO2 can be used for a smart window material and energy saved material.This paper reports that hafnium-doped vanadium dioxide nanopowders were synthesized by Deposition-Thermolysis method with hafnium oxide (HfO2) used as a substitutional dopant. The characterization and analysis of terminal resultant were determined by XRD,XPS,EDX,TEM,TG-DTA and DSC. The properties of thermochromic VO2 nanopowders have been investigated by FT-IR and the four-probe method.The results show that VO2 particle size is about 25-30nm, However, when HfO2 was added into V2O5 (with Hf/V= 3.3 atom%), Tc of VO2 decreased markedly from 69.8℃to 35℃, which was close to room temperature. Discontinuity of resistance is up to 1.5 orders of magnitude. The product of Hf-doped showed the relatively large changes of the optical transmittance and reflectance during the phase transitions that are nearly 65%. The results indicated that HfO2 was found to be exceptionally effective as a dopant for reducing transition temperature. Such a low Tc is beneficial to the application and development of smart windows materials.
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