Engineering the crystal structure of γ-[Li]-Ce2S3 red pigments for enhanced thermal stability

Abstract

The search for high thermal stability, environmentally-friendly, and low-cost red pigments for glazes remains a significant challenge in ceramic research. Here, we report a simple gas-solid reaction method to synthesis red inorganic pigments, namely γ-[Li]-Ce2S3. The effects of different molar ratio of lithium to cerium nLi/Ce (nLi/Ce ​= ​0.05, 0.10, 0.15, 0.20, 0.25, 0.30) on the phase composition, crystal structure, chromatic properties and thermal stability of pigments were systematically studied. The XRD and XPS characterization combined with Rietveled structural refinement showed that Li+ entered into the γ-Ce2S3 lattice structure to form γ-[Li]-Ce2S3 solid solutions. The two different nearest-neighbors Ce–S bond lengths in the γ-[Li]-Ce2S3 and the lattice parameters decreased with the content of nLi/Ce, while these values displayed a constant beyond nLi/Ce ​= ​0.20, indicating that the vacancies in the lattice were fully filled and Li+ no longer entered the lattice. The substitution of Li+ for Ce3+ and the elimination of the cationic vacancies in γ-[Li]-Ce2S3 led to an increase in the band gap from 1.95 to 2.00 ​eV, corresponding to a slight change in the red hue. Furthermore, from Raman spectra, a trace of cerium polysulfide as an impurity phase was found in the pigments, which was responsible for the observed dark red color of as-prepared γ-[Li]-Ce2S3. In addition, the thermal stability was evaluated by TG-DSC and the thermal stable temperature of γ-[Li]-Ce2S3 can be raised to 450 ​°C when nLi/Ce was equal to 0.20, showing that the stability of the pigments can be improved by adjusting the structural parameters.