The positron lifetime spectra of Y-doped (Ba0.6Sr0.4)TiO3 ceramics were measured, at room temperature, for Y contents of up to 0.8at%. It was found that, with increasing Y content, the variation in the positron lifetime parameters was non-monotonic and the Y content which corresponded to the knee was equal to about 0.7at%. The results showed that the Y ions substituted predominantly for Sr ions, and that this substitution introduced a large number of Sr vacancies. When the Y content increased to about 0.7at%, the Y ions began to substitute for Ba ions and the associated defects, 2YBaVSr” and 2YSrVBa”, gradually formed.

C.Q.Tang, D.M.Zhang, Q.Z.Xue: Crystal Research and Technology, 1995, 30[6], 837-41