Revealing the effect of SrO addition on NH3-assisted SrCl2 flux growth of SrTaO2N single crystals

Abstract

Perovskite-type oxynitride SrTaO₂N is of significant interest because of its photocatalytic activity and dielectric properties. SrTaO₂N was previously investigated in the forms of powder, sintered bodies, and thin films. In spite of considerable attention, there are currently insufficient experimental data to understand its physical and chemical properties. Previously, we studied the crystal growth of SrTaO₂N by an NH₃-assisted SrCl₂ flux method and produced submillimeter-sized SrTaO₂N single crystals, which is the largest size among perovskite-type oxynitride single crystals reported so far. In this study, we involve strontium oxide (SrO) as a third component, and the effect of the SrO content on the crystal growth of SrTaO₂N is investigated. As the size of SrTaO₂N single crystals increases with the addition of SrO, a binary SrCl₂–SrO flux is found to be effective for the growth of SrTaO₂N single crystals. The structural, chemical, and surface characterization of SrTaO₂N single crystals, synthesized with and without the addition of SrO, was systematically compared. The deficiency of cations and anions is slightly compensated in the SrTaO₂N single crystals with the addition of SrO, and the improvement of surface states is observed due to the reduction of defective oxygen species. These findings demonstrate that alkaline-earth metal oxides and chlorides can be an effective binary flux in the morphological and size control of single crystals of perovskite-type oxynitrides under the flux growth conditions.