Synthesis of quaternary high entropy carbonate and UV-Vis-NIR optical properties

In this study, four-element high entropy carbonate solid solutions with Mg as the primary element and three equimolar transition metal elements (Co, Ni, Zn, Fe, Mn and Cu) were successfully prepared using the hydrothermal method. The crystal structure, microstructure, color properties, and reflectance of the synthetic materials were characterized using techniques such as X-ray diffraction (XRD), scanning electron microscopy (SEM), ultraviolet-visible-near-infrared (UV-Vis-NIR) spectrophotometry. The results indicate that the existence of Cu impacts the formation of solid solution phase, especially in combination with Fe, leading to the formation of a heterophase. By changing the combination of elements, the band gap of the high-entropy carbonate was adjusted from 2.09 eV to 5.56 eV. The colorimetric coordinates, according to CIE 1976 Lab, ranged from L 34.54 ∼ 89.80, a * -22.06 ∼ 5.41, and b * -1.75 ∼ 39.38, allowing for coverage from blue to red tones. The coexistence of Cu and Fe resulted in a deep reddish-brown color, which is likely related to charge transfer transitions. Additionally, different combinations of high-entropy carbonates showed significant differences in near-infrared reflectance, reaching up to 83% in the 780 nm to 2500 nm band range, indicating potential applications in high-reflective insulation materials.