Flux growth of high entropy layered perovskite-type oxysulfide Gd2/3Y1/3Sm1/3Tb1/3Ho1/3Ti2O5S2 single crystals

Abstract

High-entropy materials represent a new class of materials that exhibit high configurational entropies and ensure the stabilisation of multiple component elements, while also exhibiting unique physical properties that permit their broad applications in fields such as energy storage, energy conversion, and catalysis. In this study, the flux growth of high-entropy layered perovskite-type oxysulfide (RE₂Ti₂O₅S₂, RE = rare-earth element) single crystals from a LiCl–CaCl₂ flux was performed for the preparation of novel hydrogen evolution photocatalysts. Initially, different combinations of rare-earth elements were investigated for substitution into the catalyst system. Subsequently, the effect of the configurational entropy was examined, and platy Gd_2−4xY_xSm_xTb_xHo_xTi₂O₅S₂ (x = 0.10–0.33) single crystals (∼1 μm size) were prepared. Transmission electron microscopy combined with energy-dispersive X-ray spectroscopy indicated that the elements were uniformly distributed within the crystals. Moreover, ultraviolet–visible spectroscopy showed that the incorporation of a high-entropy component appeared to have little effect on the electronic structure of Gd_2−4xY_xSm_xTb_xHo_xTi₂O₅S₂ (x = 0.10–0.33). This is the first report of a high-entropy layered perovskite-type oxysulfide single crystal where S_config = 1.5–1.6R. Overall, this study presents a new approach for the design of photocatalysts that are applicable to the energy and environmental fields.