Tuning the crystal chemistry and optical properties of MCuSi4O10(M = Ca, Sr, Ba) pigments via isovalent substitution and mechanochemical treatment

https://doi.org/10.1016/j.ceramint.2026.01.345

Copper layered silicates MCuSi₄O₁₀ (M = Ca, Sr, Ba) are promising inorganic pigments exhibiting intense blue color and high reflectance in the near-infrared (700–2500 nm) region. In this work, these compounds were synthesized via a flux method with subsequent mechanochemical activation. According to X-ray diffraction (XRPD) data, increasing the M²⁺ cation radius in the Ca→Sr→Ba series expands the unit cell due to longer average M−O bonds, distorting the tetrahedral-planar [CuO₄]^6- polyhedron. While mechanochemical treatment reduces agglomerate size, it does not change the unit cell parameters. Color coordinates in the CIELab space vary systematically with cation radius, whereas mechanochemical processing significantly increases lightness (L∗) and leads to color hue convergence. The highest integral solar reflectance (R∗, %) in the NIR was found for SrCuSi₄O₁₀ (76 %) and BaCuSi₄O₁₀ (75 %). The presence of an SiO₂ impurity phase detected by IR spectroscopy in CaCuSi₄O₁₀ explains its lower integral solar reflectance (56 %) compared to the other compounds. The obtained results form a holistic understanding of the influence of crystal chemical factors and mechanical processing on the optical properties of MCuSi₄O₁₀ and can serve as a basis for the rational design