A facile one-step annealing route to prepare thermochromic W doped VO2(M) particles for smart windows

W doped VO2 is a promising thermochromic material for smart windows but its preparation process is usually complicated and time-consuming. In this work, W doped VO2 (V1-xWxO2) particles were synthesized via a novel and facile one-step annealing method where V2O5 and (NH4)(10)H-2(W2O7)(6) composite powders were used as precursor. The solid state reaction between the products (VO2 and WO3) was considered to promote the diffusion of W elements into VO2 lattice during the annealing process which was confirmed by the XPS and EDS results. As increasing the content of (NH4)(10)H-2(W2O7)(6), the phase transition temperature of V1-xWxO2 was significantly reduced from 62.7 degrees C to 46.7 degrees C, meanwhile the corresponding V1-xWxO2/WO3 composite based films showed a same trend in the solar modulation efficiency from 10.7% to 7.8%. In addition, these films exhibited satisfactory visible transmittance of 56%-62%. Especially, the film based on the sample with V/W molar ratio of 8:1 showed a good thermochromic performance (T-MIT = 55.6 degrees C, Delta T-sol = 9.7% and T-lum = 60.8%) for smart windows. Therefore, this method based on the traditional solid-based reaction could provide a new way for elements doping into VO2 to promote application of VO2 in smart windows due to its low cost, repeatability and scale production.