Influence of microstructure on the properties of Sr0.5Pb0.5TiO3 V-shaped PTCR

Lanthanum-doped Sr0.5Pb0.5TiO3 semiconducting ceramics were prepared by the solid state reaction technique with excess PbO additive. Samplesʹ resistivities rise about 5 orders of magnitude above the Curie temperature (Tc≈115 °C) and their negative temperature coefficient of resistivity (NTCR) increases with an increase of the sintering temperature. The crystalline structure, microstructure and compositional distribution were investigated using XRD, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) with X-ray energy dispersive analyses (EDAX), respectively. The distribution of Pb, Sr and Ti in the grain boundary layer has been shown to be similar to that in the grain interior. It is assumed that the PbO additive compensates Pb loss and keeps the Pb/Ti ratio stable in the grain boundary layers, which results in the low room temperature resistivity and weak NTCR effects.