Synthesis and characterization of novel yellow-green Cr, Zn-codoped Ba(Mg6Ti6)O19 pigments with high NIR reflectance

This work reports a series of yellow-green near-infrared (NIR) reflective pigments, Ba(Mg 6-x-y Zn y Ti 6-x Cr 2x )O 19 (x = 0–1.0, y = 0–2.5), with strong NIR reflectivity for solar thermal energy regulation. Comprehensive analyses were carried out to characterize the obtained pigments including X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, UV–Vis–NIR spectrophotometry, and CIE L*a*b* color measurement. Absorption spectra of Ba(Mg 6-x Ti 6-x Cr 2x )O 19 showed that the yellow-green absorption is attributed to the octahedrally coordinated Cr 3+ with d-d electron transitions of 4 A 2 (F)→ 4 T 1 (F) and 4 A 2 (F)→ 4 T 2 (F). However, their broad absorption peak centered at 1200 nm severely deteriorated the insulating properties of the pigments. Through substituting Mg with Zn, the obtained pigment Ba(Mg 2.5 Zn 2.5 Ti 5 Cr 2 )O 19 showed an excellent NIR solar reflectance (R* = 67 %) with color performances (L* = 61.98, a* = −18.72, b* = 22.23). EnergyPlus simulation results show that for a warm city (Haikou), the Ba(Mg 2.5 Zn 2.5 Ti 5 Cr 2 )O 19 coating for the external surface of a model house (TSR = 35 %, R* = 55 %) can reduce annual cooling energy consumption by 8 % of the house.