Thermochromic properties of pure NiTiO3 and its Cu- or Co-doped derivatives

Nickel titanate is a yellow-brown pigment which adopts the ilmenite crystal structure as corundum and hematite. Since Cr doped Al2O3 and Fe2O3 present a thermochromic behavior, NiTiO3 was also studied for its potential ability to change colour with temperature. Powders were synthesized via a modified Pechini method followed by a calcination step at 700 degrees C. The thermochromic properties in the 20 degrees C-400 degrees C temperature range were collected via the determination of the colorimetric L*a*b* parameters. Namely, the hue continuously shifts from yellow-brown to red-brown, with L*a*b* parameters moving from 60.4/19.2/58.5 to 42.9/30.5/43.1. This colour change is fully reversible even after several cycling. Temperature dependent UV-vis spectroscopy showed that the transparency window at 550-650 nm at room temperature shifts to 575-650 nm at 400 degrees C. This fully explains the observed colour change. Finally, the effects of Cu or Co doping on NiTiO3 optical and thermo-chromic properties were also investigated.

Automated summary

Nickel titanate is a yellow-brown pigment with a crystal structure similar to corundum and hematite. It has been found that nickel titanate can change its color with temperature, exhibiting thermochromic properties. The powders were synthesized using a modified Pechini method and then subjected to calcination at 700 degrees C. The thermochromic behavior in the temperature range of 20 degrees C to 400 degrees C was studied by determining the colorimetric L*a*b* parameters. The hue continuously shifts from yellow-brown to red-brown, with L*a*b* parameters changing from 60.4/19.2/58.5 to 42.9/30.5/43.1. It was also observed that the transparency window shifted from 550-650 nm at room temperature to 575-650 nm at 400 degrees C, explaining the color change. Additionally, the effects of Cu or Co doping on the optical and thermochromic properties of nickel titanate were investigated.