Positive temperature coefficient of resistivity (PTCR) ceramics of 0.912(Ba 1+x TiO 3 )-0.088(Bi 0.5 Na 0.5 TiO 3 ) (BT-BNT) (x = À0.03 to 0.03) were prepared using the mixed oxide route and sintered at 1340°C for 4 h. Products were predominantly single phase with a tetragonal structure and grains in 2-6 lm size containing 90°ferroelectric domains. Samples with Ti/Ba > 1 contained second-phase Ba 6 Ti 17 O 40 . HRTEM and aberrationcorrected Z-contrast high angle annular dark field scanning transmission electron microscopy (HAADF-STEM) suggested that the dopants, Bi and Na, occupy the Ba site of the perovskite lattice, and revealed the presence of dissociated dislocations in x = À0.03 and x = 0.00 materials. The interval between two partial dislocations was 1.9-3.4 nm, yielding stacking fault energies of 363-649 mJ/m 2 . The PTCR behavior of the ceramics increased with Ti/Ba content, reaching a maximum of six decades change in resistivity for x = À0.03. The anomalous increase in resistivity depends critically on stoichiometry, increasing with the Ti/Ba ratio; this in turn is directly correlated with an increase in the amount of secondphase Ba 6 Ti 17 O 40 , an increase in the stacking fault energy, and an increase in the tilt angle of the grain boundaries.

LaAlO 3 -SrTiO 3 [(1-x) LAO-xSTO] ceramics were prepared by a conventional solid phase reaction method using high purity reagents. To investigate influence of the sintering atmosphere, the samples were sintered under oxygen partial pressures from 97.7% to 6.3%. The permittivity was rarely affected by the sintering atmosphere. However, Qf values of 0.6LAO-0.4STO and 0.5LAO-0.5STO were strongly affected by the atmosphere. Cathode luminescence examination showed that a low oxygen partial pressure introduced oxygen defects in these materials. It was confirmed by far infrared measurement that the oxygen defects barely affected the lattice vibration. The electrical conductivity of these two solid solutions was confirmed, and it was inferred that an oxygen defect introduced a conductive electron in their structures. The loss tangent calculated from the electrical conductivity was approximately in agreement with that obtained by microwave measurement in the 0.5LAO-0.5STO solid solution. The possibility that the induced electron may act like a small-radius polaron was shown by Ti XPS spectra. Further investigation is needed to clarify the character of the electron.