Growth of Millimeter-Sized BaTaO2N Single Crystals by an NH3-Assisted BaCl2 Flux Method

Abstract

Perovskite-type oxynitrides have attracted considerable attention due to their excellent photocatalytic activity and dielectric properties, making them promising candidates for solar energy conversion and electronic applications. However, despite extensive efforts to synthesize perovskite-type oxynitrides in various forms, such as powders, sintered ceramics, films, epitaxial layers, and nanocrystals, the growth of large, high-quality single crystals has remained a significant challenge. In recent years, their single crystals have been studied to understand their fundamental properties. One of the central challenges in obtaining accurate properties is the growth of the larger perovskite-type oxynitride single crystals. In this work, millimeter-sized single crystals of BaTaO₂N are successfully grown by an ammonia (NH₃)-assisted BaCl₂ flux method for the first time. The growth mechanism of the single crystals is investigated by varying crystal growth conditions. Systematic studies reveal that the dual growth mechanism is driven by flux evaporation and controlled cooling of the non-aqueous solution. The as-grown crystals are comprehensively characterized, confirming their chemical composition, surface chemical states, and dielectric properties of the BaTaO₂N single crystals. The findings demonstrate a promising approach for the growth of single crystals of perovskite-type oxynitrides and pave the way for their integration into next-generation functional devices in the future.