[en] Bi_2Te_3 single crystals were prepared by the solid-state reaction method. The effect of the vacuum on the growth of Bi_2Te_3 single crystals was studied with varying the oxygen content by controlling the air pressure in the silica tube. High quality Bi_2Te_3 single crystals have been obtained and there is no influence on the growth by an extremely small amount of oxygen in a high vacuum at 1.0 × 10"−"3 Pa. As the air pressure is increased at 1.0 × 10"−"2 Pa, oxygen only mainly impacts on the growth of the surface for the prepared samples. Micron-sized rod-like structure and flower-like clusters are observed on the surface. For the samples prepared at 1.0 × 10"−"1 Pa, x-ray diffraction data show that the yellow part on the surface is Bi_2TeO_5, while the Bi_2Te_3 single crystal is still the major phase as the inside part. More interestingly, various crystal morphologies are observed by scanning electron microscope for Bi_2Te_3 near the boundary between Bi_2Te_3 and Bi_2TeO_5. Possible growth mechanisms for Bi_2Te_3 with different morphologies are discussed in detail. (paper)