Molecular dynamics calculations reveal mechanism for cesium desorption in cesium-doped tungsten bronze

Capable of absorbing near infrared light (NIR) and transmitting visible light, cesium-doped tungsten bronze (CWO) nanoparticles are becoming increasingly popular as NIR shielding material for window glass, saving energy otherwise required for cooling building and car interiors. Hot and humid environments, however, can bleach CWO particles and degrade their ability to prevent infrared light from passing through the windows.

A recent article uses first principles computer modeling to better understand how such bleaching occurs. Yoshio et al. report their findings on the desorption of cesium from CWO in the presence of water. Using accelerated molecular dynamics calculations to trace cesium atoms detaching from Cs_0.33WO₃ nanoparticles, the group constructed the material’s potential-pH diagram and identified key features of the reaction mechanism.

The findings point to ways to prevent such bleaching from occurring, said Satoshi Yoshio, an author on the paper.

“The phenomenon of degradation has been rarely targeted by first principles calculations thus far,” Yoshio said. “The application of first-principles molecular dynamics, as well as the combined analysis of the potential-pH diagram for environmental equilibrium are considered novel in this work.”

While their initial calculations suggested the detachment reaction was reversible, which contradicts experimental observations, they were able to use the potential-pH diagram to factor in the oxidation of detached (WO₃)⁻ molecules and resolved the paradox. Their final derived atomistic mechanism agrees with observed experimental results.

The group proposed that steric hindrance effects of anion substitutions with large ions on the surface of glass could act as a countermeasure to suppress the cesium desorption. They hope to apply similar procedures to elucidate the surface reaction mechanisms of other functional nanoparticles.

Source: “Cesium desorption mechanism in Cs_0.33WO₃ by first-principles molecular dynamics calculations,” by Satoshi Yoshio, Kenji Adachi, and Momoji Kubo, Journal of Applied Physics (2019). The article can be accessed at https://doi.org/10.1063/1.5097416 .