Two-Step Growth of Layered Perovskite Y ₂ Ti ₂ O ₅ S ₂ Yields Faceted Crystals with Controlled Size and Morphology

Understanding the growth process of photocatalytic materials is crucial for the rational design of crystals with a controlled morphology and enhanced performance. Y2Ti2O5S2 (YTOS) is a promising visible-light-responsive photocatalyst. However, the lack of understanding regarding its formation mechanism hinders the growth of high-quality YTOS crystals. Here, we report the solid-state synthesis and flux growth of YTOS via a two-step process to produce well-faceted, plate-like crystals with sizes ranging from 1 to 3 μm. This method enables the realization of distinct crystal morphologies compared with those obtained using conventional one-step solid-state and flux-growth techniques. Transmission electron microscopy reveals that the lateral facets of YTOS are primarily indexed to the (100) and (110) planes. In situ X-ray diffraction experiments show that Y2O2S forms as a key intermediate at temperatures above 600 °C. Density functional theory calculations further indicate that Y2O2S serves as a crucial precursor despite the thermodynamic proximity of Y2Ti2O7 in the Y–Ti–O–S space system. The proposed two-step growth method offers a new strategy for controlling the crystal growth of YTOS and insights into its formation mechanism, advancing the development of efficient photocatalysts for solar-driven applications.