Cationic Defect Engineering for Controlling the Infrared Absorption of Hexagonal Cesium Tungsten Bronze Nanoparticles

Abstract

Cesium tungsten bronzes (Cs0.32WO3) have attracted much attention as a near-infrared absorbing material. We report the successful synthesis of highly crystalline and high purity Cs0.32WO3 nanoparticles through a spray pyrolysis route. Careful analyses disclosed the presence of cationic defects, that is, a tungsten deficiency and insufficient Cs doping in the Cs0.32WO3 nanoparticles. These cationic defects can be controlled by facile heat treatment in a mildly reducing atmosphere. In particular, we clarify that the tungsten deficiency is a key factor among the cationic defects to obtain high near-infrared absorption properties. Furthermore, this study clearly demonstrates the precise tunability of the optical properties by means of the lattice constants of the Cs0.32WO3 crystal. The realized range of lattice constants is significantly wider than those previously reported. These findings should contribute to the engineering of Cs0.32WO3 structure and properties.

Cation Defect Mediated Phase Transition in Potassium Tungsten Bronze

“…The e-beam irradiation effects on the phase transitions were discussed. This work offers detailed information on the phase transformation mechanisms of K x WO 3 induced by cationic defects, which could also serve as a guidance for understanding the phase instability in other tungsten bronzes, e.g., Na x WO 3 , Cs x WO 3 , and others. ,,,, …”

“…For instance, by facile heat treatment in a mildly reducing atmosphere, the increasing ratio of W 5+ can improve the near-infrared absorption performance. 19,20 In addition, the different contents of K + could result in structural diversity, yielding a variety of novel properties such as a metal−insulator transition, 21,22 charge-density-wave transition, 23 and superconductivity. 24 It is thus of utmost importance to have a thorough knowledge of the influence of the cationic defects on the structure of K x WO 3 during heating, which unfortunately is far from well-developed.…”

“…Potassium tungsten bronze (K x WO 3 , 0.18 < x < 0.57), a non-stoichiometric compound with one-dimensional channels, exhibits high thermal stability and is a promising material for many technological applications at high temperatures, such as ion batteries, thermoelectric materials, , infrared shielding, gas sensing, electrocatalysis, and heat shielding. − In general, the performance is highly dependent on the two kinds of cationic defects, i.e., K and W vacancies, both of which are sensitive to thermal effects. For instance, by facile heat treatment in a mildly reducing atmosphere, the increasing ratio of W 5+ can improve the near-infrared absorption performance. , In addition, the different contents of K + could result in structural diversity, yielding a variety of novel properties such as a metal–insulator transition, , charge-density-wave transition, and superconductivity . It is thus of utmost importance to have a thorough knowledge of the influence of the cationic defects on the structure of K x WO 3 during heating, which unfortunately is far from well-developed.…”

Advances in Energy‐Efficient Plasmonic Electrochromic Smart Windows Based on Metal Oxide Nanocrystals

“…have proved that the changes of crystal shape and structure are the key factors affecting the NIR LSPR absorption of bronze phase tungsten oxide. [108][109][110][111][112][113][114][115][116] However, there has been little research into plasmonic EC applications. In contrast, oxygen vacancy self-doping is the most widely reported method to tailor the LSPR band of tungsten oxide NCs.…”

Improving the Crystallinity and Purity of Monodisperse Ag Fine Particles by Heating Colloidal Sprays In-Flight

“…Both gas and liquid phase methods can be used to produce fine particles. Gas phase techniques have several advantages, such as the formation of particles with high levels of crystallinity and superior purity, although aggregation and sintering of these particles can occur as a result of the high reaction temperature. − Therefore, a post-treatment consisting of dispersion or grinding is required. − In contrast, the liquid phase methods can produce highly dispersed fine particles with homogeneous morphologies and narrow particle size distributions. However, the crystallinity and purity of the products are relatively low compared with those prepared by high-temperature gas phase methods because of the low reaction temperature and the requirement to use high concentrations of additives such as dispersion agents. − A process for the synthesis of fine particles combining the advantages of gas and liquid phase methods (that is, forming highly dispersed, fine particles while maintaining a high degree of crystallinity and purity with a narrow particle size distribution) would be beneficial in the fields of powder technology and functional materials.…”