Structural, electronic, and optical properties of CaCoSi2O6 and Ca2CoSi2O7 blue pigments: A combined experimental, DFT+U, and BSE study

Abstract

The exceptional characteristics of pigments, such as their high thermal stability, affordable production costs, and easy manufacturing procedures, are the reasons for their steady growth in industrial applications. On the other hand, the use of theoretical computations to forecast pigment color is a novel and significant area of study. In this study, CaCoSi2O6 (co-pyroxene) and Ca2CoSi2O7 (co-akermanite) pigments were synthesized using a conventional ceramic method. We studied the structural, magnetic, electronic, optical, and colorimetric properties of the pigments within experimental and theoretical approaches. The structural characteristics of the pigments were investigated by X-ray diffraction technique (XRD), Scanning Electron Microscope (SEM), UV–visible (UV–Vis) spectroscopy, and color measurement (CIE L*a*b*) colorimetry methods. Also, Hubbard Density Functional Theory (DFT + U) calculations were performed using 40 atoms of co-pyroxene and 24 atoms of co-akermanite. We employed the Bethe-Salpeter equation (BSE) method for studying the absorption spectrum and color of pigment samples. The theoretical energy gap values for the CaCoSi2O6 and Ca2CoSi2O7 structures were determined to be 4.2eV and 3.5eV, respectively. While the direct experimental band gap for CaCoSi2O6 and Ca2CoSi2O7 is about 4eV and 3.9eV, respectively. Comparing the outcomes, it can be inferred that the BSE method represents a valuable approach to predicting the absorption spectra and color features of pigment structures.