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.