Positive temperature coefficient of resistivity ceramics of 0.912(Ba1+xTiO3)-0.088(Bi0.5Na0.5TiO3) ( with x = -0.03 to 0.03) were prepared by using the mixed oxide route and sintered at 1340C for 4h. The products were predominantly single-phase, with a tetragonal structure and with grains which were 2 to 6μm in size and contained 90° ferroelectric domains. Samples with Ti/Ba > 1 contained second-phase Ba6Ti17O40. High-resolution and aberration-corrected Z-contrast high-angle annular dark-field scanning transmission electron microscopy suggested that the dopants, Bi and Na, occupied the Ba site of the perovskite lattice and revealed the presence of dissociated dislocations in x = -0.03 and x = 0.00 materials. The interval between two partial dislocations was 1.9 to 3.4nm, yielding stacking-fault energies of 363 to 649mJ/m2. The positive temperature coefficient of resistivity behavior increased with Ti/Ba content; reaching a maximum of six decades change in resistivity for x = -0.03. The anomalous increase in resistivity depended critically upon stoichiometry, increasing with the Ti/Ba ratio. This in turn was directly correlated with an increase in the amount of second-phase Ba6Ti17O40, an increase in the stacking-fault energy, and an increase in the tilt-angle of the grain boundaries.

(Ba1+xTiO3)-(Bi0.5Na0.5TiO3) Lead-Free, Positive Temperature Coefficient of Resistivity Ceramics: PTC Behavior and Atomic Level Microstructures. Y.Kaneko, F.Azough, T.Kida, K.Ito, T.Shimada, T.Minemura, B.Schaffer, R.Freer: Journal of the American Ceramic Society, 2012, 95[12], 3928-34