Flux growth of Sr2Ta2O7 crystals and subsequent nitridation to form SrTaO2N crystals

Abstract

Highly crystalline, idiomorphic Sr₂Ta₂O₇ and SrTaO₂N crystals were successfully grown by a SrCl₂ flux cooling method and followed by a nitriding treatment using NH₃ gas, respectively. The flux-grown Sr₂Ta₂O₇ crystals had a columnar structure with flat and well-developed {010}, {061}, and {150} faces. The lattice parameters of the Sr₂Ta₂O₇ crystals were determined to be a = 0.398, b = 2.716, and c = 0.570 nm. The TEM images indicated that the flux-grown Sr₂Ta₂O₇ crystals had a mature columnar structure with high crystallinity. The shapes and sizes of the SrTaO₂N crystals were in good agreement with the original Sr₂Ta₂O₇ crystals, and they consisted of numerous small crystals with approximate dimensions of 50 nm and high crystallinity. The lattice parameters of the SrTaO₂N crystals were a = 0.570 and c = 0.809 nm. The optical absorption edges of the Sr₂Ta₂O₇ and SrTaO₂N crystals were approximately 275 and 600 nm, respectively, and the band gaps were estimated to be located at 4.5 and 2.1 eV, respectively.