Synthesis of Ba_1−xSr_xYSi₂O₅N and Discussion based on Structure Analysis and DFT Calculation

Abstract

　Cation substitution for inorganic solid materials is a practical approach to control their functions. Here, synthesis, structure analysis, density functional theory (DFT) calculation of novel oxynitrides Ba_1−xSr_xYSi₂O₅N, and investigation of their photoluminescence properties with Eu²⁺- or Ce³⁺-activator were conducted. Single crystal and powder X-ray analyses revealed that Ba_1−xSr_xYSi₂O₅N were formed at x ≤ 0.75 and they were isotypic while the synthesis of SrYSi₂O₅N (x = 1) was not achieved by any synthesis conditions examined. Based on phonon calculation, it was concluded that the synthesis of SrYSi₂O₅N with the isostructure to BaYSi₂O₅N was impossible due to the thermodynamical unstability. Substitution of Ba with Sr decreased the average bond length of AE-(O,N) (AE = Ba and Sr) and increased distortion of AE sites. On the other hand, coordination environments of Y sites were rarely affected by the substitution. As a result, redshift and broadening of emission spectra for Eu-doped samples were observed, whereas there was almost no spectral change in Ce-doped samples.