AbstractThe positron lifetime spectra in Y‐doped (Ba0.6Sr0.4)TiO3ceramics have been measured at room temperature for Y contents of 0–0.8 at. %. It was found from the experiments that with increasing Y content, the variation of the positron lifetime parameters is nonmonotonic, and the Y content corresponding to the knee is about 0.7 at. %, which is much larger than the La content corresponding to the knee in the La‐doped BaTiO2(TANG 1994a). The experimental results show that the Y ions substitute predominantly for Sr ions, and this substitution induces a large number of Sr vacancies; when the Y content increases to about 0.7 at. %, the Y ions begin to substitute for Ba ions, and then the associated defects (2 YBaV“SrSr) and (2 YSrV”BaBa) form