Evolution of the chemical surroundings of vacancy complexes in Sb-doped ([Sb]=2×1018 and 2×1019 cm−3) Si0.8Ge0.2 was studied with positron annihilation spectroscopy in Doppler broadening mode. The study was performed by annealing the samples both isochronally and isothermally. Defect evolution was observed at the temperature range 450–650 K. Both treatments were shown to induce changes in the chemical surroundings of the E-centers via introduction of Ge near the defects. Moreover, Sb was found to hinder these changes by stabilizing the E-centers and thus preventing them from finding Ge. The stable state reached after the anneals was found to differ from that measured from an as-grown sample. This difference was deemed to be the result of Ge gathering in small clusters during the annealing thus breaking the initially random Ge distribution.