Theory of the color change ofNaxWO3as a function of Na-charge doping

Abstract

We report theoretical investigations of the coloration of ${\text{WO}}_{3}$ upon charge insertion using sodium tungsten bronze $({\text{Na}}_{x}{\text{WO}}_{3})$ as a model system. Our results explain well the systematic color change of ${\text{Na}}_{x}{\text{WO}}_{3}$ from dark blue to violet, red-orange, and finally to golden yellow as sodium concentration $x$ increases from 0.3 to unity. Proper accounts for both the interband and the intraband contributions to the optical response are found to be very important for a detailed understanding of the coloration mechanism in this system.