Combined experimental and DFT study on high-temperature thermochromism of Co-doped LaCrO3 coating for thermal indicator

Noncontact temperature measurement using thermochromic materials is vital in the field of temperature indication, but the related mechanisms behind thermochromic behavior are diverse and high complexity, and the color-temperature correspondence is poorly explored. This paper systematically studied the thermochromic mechanisms and color-temperature correspondence in the cobalt-doped LaCrO3 coatings via experiment and density functional theory study. The coatings appear reversible thermochromism from green to black with temperature and composition, functions from room temperature to 700 degrees C. This thermochromism is attributed to the lattice expansion and bandgap reduction as the temperature increase, and a model of temperature effect bandgap was proposed. Meanwhile, the coating temperature can be inferred from the color change because the CIE chromaticity coordinate of the coating varies linearly with temperature, and the mean relative error of thermochromic measurements is 8.28%. Furthermore, the cobalt doped introduces impurity energy levels and enhances the interaction between photons and carriers, which reduce the bandgap and increase the absorption in the visible spectrum resulting in darker colors. This work provides a stable and efficient high-temperature thermochromic coating that has a wide thermochromic temperature range and clear color-temperature correspondence, which shows broad application prospects in the field of thermal indication at high temperatures.