A Stable BaAl12-xNixO19-δ Sky-Blue Pigment with High NIR Reflectance for Cooling Ceramic Glazes

In this study, a series of BaAl 12- x Ni x O 19-δ ( x =0, 0.2, 0.4, 0.6, 0.8, 1.0) blue pigments were successfully synthesized via a solid-state reaction method. The results confirmed that Ni 2+ ions successfully substituted Al 3+ within the host lattice without altering the crystal structure. The synthesized pigments exhibited a distinct blue hue, attributed to the characteristic d-d transition in Ni 2+ ions. Additionally, the pigments demonstrated high NIR solar reflectance (ranging from 68.08% to 98.82%) within the wavelength range of 700-2500 nm, which is markedly superior to traditional cobalt blue (39%). In a practical thermal insulation test, a ceramic body coated with the BaAl 11.6 Ni 0.4 O 19-δ glaze showed a remarkable surface temperature reduction of 21.66% compared to an uncoated substrate. The combination of excellent color stability in glaze and superior NIR reflectance makes this BaAl 12- x Ni x O 19-δ system a highly promising candidate for use as a cool pigment in energy-efficient building materials, such as reflective coatings for roofs and walls.