Grain-boundary surface states of (Ba,Pb)TiO/sub 3/ positive temperature coefficient ceramics doped with different additives and its influence on electrical properties

The electrical properties of positive temperature coefficient of resistance (PTCR) ceramics of composition (Ba,Pb,La)TiO/sub 3/ prepared from commercial BaTiO/sub 3/ powders doped with different additives were studied. It was proposed here that different additives might have generated the corresponding number of possible surface states, such as, the segregation behavior of Mn ions (3d transition metal ions), oxygen adsorption reaction resulting from BN addition, the action of Ca replacing the Ti sites (Ca/sub Ti/") and the natural intrinsic defects (V/sub Ba/", V/sub Pb/"). In general, some experimental derivations were also offered that majority of the surface states, which possessed their individual surface energy level, possibly coexisted onto the grain surface. Utilizing the concept of the coexistence of different types of surface states in the energy band, a satisfactory point-to-point agreement was obtained between the measured result and calculated values for the resistivity curve. Our experimental results were analyzed based on the terms of the Heywang-Jonker model and have shown that the assumption of a Hewang barrier was a reasonable approach for our set of samples; however, the distribution and types of grain-boundary acceptor states classification were required.