Improvement of near-infrared (NIR) reflectivity and black color tone by doping Zn into the CaMnTiO structure.

Inorganic black pigments with thermal barrier characteristics, CaMn TiZn O (0 ≤ ≤ 0.10), were synthesized using a conventional solid-state reaction method in order to improve the blackness without decreasing the near-infrared (NIR) reflectance of a CaMnTiO pigment, which was previously reported by our group. The composition was optimized to provide both high blackness and NIR reflection characteristics. As a result, the NIR solar reflectance value ( ) of CaMnTiZnO ( = 74.6%) became larger than that of CaMnTiO ( = 71.7%), and the black color tone of the former (* = 23.2, * = +2.81, * = +0.83, = 2.93) was improved in comparison with that of the latter (* = 24.4, * = +4.30, * = +2.72, = 5.09). This improvement is caused by the introduction of strain into the [MnO] octahedra and a decrease in the manganese ion concentration. The value of the CaMnTiZnO pigment was also larger than those of the commercially available pigments ( < 53.0%). Therefore, CaMnTiZnO has potential to be an inorganic black pigment for thermal shielding.