A study on the properties of (Y, Mn) co-doped Sr0.5Pb0.5TiO3 thermistors

(Y, Mn) co-doped Sr0.5Pb0.5TiO3 ceramics were fabricated by solid state reaction method. The samples' room temperature resistivities increase and their negative temperature coefficient of resistance (NTCR)-positive temperature coefficient of resistance (PTCR) composite effects become strong with increasing Mn concentration. The investigations of scanning electron microscope and complex impedance spectra show that Mn addition confines the grain growth and increases the grain boundary resistance. In addition, electron paramagnetic resonance spectra confirm that the Mn impurities are in forms of high valence below the Curie temperature (Tc) and divalent Mn2+ cations appear above Tc. It is assumed that partial Mn cations can trap the electrons and be reduced to divalent Mn2+ cations during phase transition, which benefits to improving the PTCR effect of (Sr. Pb)TiO3-based thermistors. And the NTCR effect below Tc should be closely related to the acceptor defects in the grain boundary layers. (C) 2002 Elsevier Science B.V. All rights reserved.