We report the evolution of superconductivity and the phase diagram of the KxFe2-ySe2-zTez (z = 0-0.6) crystals grown by a one-step synthesis. The one-step synthesis is much simpler than a conventional process to grow the KxFe2-ySe2 system. No structural transition is observed in any crystals, while lattice parameters exhibit a systematic expansion with increasing Te content. The T c exhibits a gradual decrease with increasing Te content from K at z = 0 to K at z = 0.5, followed by a sudden suppression of superconductivity at z = 0.6. Upon approaching a Te concentration of 0.6, the shielding volume fraction decreases and eventually drops to zero. Simultaneously, hump positions in the ρ-T curve shift to lower temperatures. These results suggest that isovalent substitution of Te for Se in KxFe2-ySe2 crystals suppresses the superconductivity in this system.
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