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Herein, we report the details of the synthesis and crystal growth of a lead-free perovskite derivative Cs2TeI6 crystal, which reveals long-term environmental stability. The synthesis process is optimized to obtain pure Cs2TeI6 polycrystals, and to eliminate the formation of residual CsI resulting from high vapor pressure. Subsequently, the Cs2TeI6 single crystal with dimensions of Φ10 mm × 55 mm is grown by the vertical Bridgman method. The as-grown 0-D structural Cs2TeI6 crystal exhibits a high resistivity of 9.92 × 1011 Ω cm, and resulting mobilities of 4.03 ± 0.33 cm2 V−1 s−1 and 9.40 ± 0.45 cm2 V−1 s−1 for electrons and holes, respectively. The Au/Cs2TeI6/Au device shows a good response for optoelectronic and X-ray detection, with a relatively high X-ray sensitivity of 27.8 μC Gy−1 cm−2 and a low detection limit of 72.5 nGy s−1. [ABSTRACT FROM AUTHOR]