Effect of annealing temperature on the structural and solar heat shielding performance of NiTiO 3 nanopowder

Abstract Nickel titanate (NiTiO 3 ) is a bimetallic oxide with potential applications in solar heat shielding coatings. Most prior researches have focused on the photocatalytic behavior of NiTiO 3 but are limited to explore on reflective performance. In the paper, NiTiO 3 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 NiTiO 3 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 NiTiO 3 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 NiTiO 3 powders was found to be decrease as treatment temperature increased. Temperature higher than 700 °C, results showed further crystallization of NiTiO 3 , due to Ni 2+ ion d-d transitions ( 3 A 2g  →  3 T lg (P)) and transfer of amorphous NiTiO 3 structure to an ilmenite structure. These results indicate that when annealing temperature is increased the microstructure and crystal size of NiTiO 3 powders are altered and the performance of optical reflection is changed.