P-type Sb2−xBixTe3 crystals with various chemical compositions (x = 0.40, 0.44, 0.47, 0.50, 0.53, 0.56 and 0.60) were fabricated by zone melting method. Transmission electron microscopy and energy dispersive X-ray microanalysis were performed to characterize the evolutions of defects on the sites of Bi, Te and Sb atoms in the lattice. Study of Sb2−xBixTe3 structure reveals the formation of Bi2Te3 in which native defects are a consequence of overstoichiometry of Bi atoms in Bi2Te3 single crystal. Thermoelectric properties, including Seebeck coefficient (α), electrical conductivity (σ), thermal conductivity (k), and Hall constant were measured at room temperature. In terms of thermoelectric properties, increasing Bi2Te3 content (x) decreased carrier (hole) concentration (and σ, as a result) and increased α. The maximum figure-of-merit (Z = α2σ/k) of 2.7×10−3 K−1 was obtained at about 300 K for 25%Bi2Te3 − 75%Sb2Te3 with 3 wt% excess Te recommended for thermoelectric properties modification. Added Te is considered not only as a dopant, but also to compensate the deficiency of Tellurium understoichiometry. The results compared with reports of several authors to evaluate the dependency of parameters on sites of the atoms. The novelty of this work is to present the sites of the atoms in the lattice of the ternary compounds and the effect of defects occurred due to the atomic sizes of the Bi, Sb and Te.