Effect of annealing temperature on the structural and solar heat shielding performance of NiTiO3 nanopowder

Nickel titanate (NiTiO3) is a bimetallic oxide with potential applications in solar heat shielding coatings. Most prior researches have focused on the photocatalytic behavior of NiTiO3 but are limited to explore on reflective performance. In the paper, NiTiO3 ultrafine nanopowders were synthesized by the sol-gel method. Thermogravimetric and differential scanning calorimetry, X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, Raman spectroscopy, and UV-Vis-NIR-DR spectro-photometry were employed to investigate the structural and optical properties of samples at different treatment temperatures. The average crystal size of synthesized NiTiO3 powder in 500-900 °C regions was found to be 13.8 ± 0.02-80.2 ± 0.06 nm. Ultraviolet-visible (UV-vis) near infrared (NIR) diffuse reflectance spectra study showed that synthesized at 500 °C for 10 h NiTiO3 nanoparticles showed higher solar reflection of 40.5 ± 0.04% in the NIR region (700-2500 nm) than other temperature samples according to particular computational formulation with experimental results. The solar reflective ability in the NIR region of NiTiO3 powders was found to be decrease as treatment temperature increased. Temperature higher than 700 °C, results showed further crystallization of NiTiO3, due to Ni2+ ion d-d transitions (3A2g → 3Tlg(P)) and transfer of amorphous NiTiO3 structure to an ilmenite structure. These results indicate that when annealing temperature is increased the microstructure and crystal size of NiTiO3 powders are altered and the performance of optical reflection is changed.