Title: STUDY OF BATIO$_3$ CERAMICS DOPED WITH MN AND CE OR NB AND SR
Author(s): A.M.Slipenyuk, M.D.Glinchuk, I.P.Bykov, L.P.Yurchenko, V.A.Mikheev, O.A.Frenkel, V.D.Tkachenko, E.P.Garmash (Institute for Problems of Materials Science of the National Academy of Sciences of Ukraine, 3 Krjijanovskogo Str., 03680 Kiev-142, Ukraine)

ESR study of BaTiO$_3$ ferroelectrics doped with cerium or with niobium and strontium, both types of samples being doped with manganese, was performed at room temperature. In the samples of the first type the most intensive line with $g$-factor 1.9612 was shown to originate from paramagnetic center Ti$^{3+}$--Ce$^{3+}$. The small intensity line was related to Fe$^{3+}$--V$_{\mathrm{O}}$ center, which can be unavoidable impurity in BaTiO$_3$. In the samples doped with strontium, the six lines intensive spectrum, which corresponds to hyperfine structure of Mn$^{2+}$, was observed. The intensity of the spectrum was shown to decrease with strontium concentration increase. This effect was supposed to be related to the decrease of the grain sizes that results in migration of manganese and, possibly, niobium ions. The influence of these impurities, of their charge states and positions in crystalline lattice of BaTiO$_3$ on the PTCR effect is discussed.

Key words: BaTiO$_3$ ceramics, impurities, positive temperature coefficient of resistivity
PACS: 72.80.Sk, 76.30.Fc, 77.84.Dy