Impurities in barium titanate posistor ceramics

The investigation of impurity centres in BaTiO3 ceramics doped with rare-ea rth ions Y, La, Lu, Sm, and Dy with concentration 0.1-0.5 at.% were carried out by ESR methods at 160K<480K. It was shown that the most intense ESR li nes belong to paramagnetic complex Fe3+-V-0 and Ti3+-Ln(3+) (Ln is rare-ear th ion, V-0 is oxygen vacancy). Exponential broadening of the ESR line of F e3+ V-0 centre in the tetragonal phase was observed. The origin of this bro adening is discussed. Analysis of the obtained results along with conductiv ity data made it possible to find the characteristic concentration n(c)appr oximate to 0.2-0.3 at.% of rare-earth ions: at n<n(c)or n>n(c) the rare-ear th ions. except Lu, are substituted for Ba2+ Ti4+ respectively. The role of this phenomenon as well as of the revealed paramagnetic centres in the app earance of positive temperature coefficient of resistivity is discussed.