Abstract: Liquid-phase sintering method was used to prepare BaTiO₃ powders and the structure and electrical properties of (1-x)BaTiO₃+(x)La_2/3Sr_1/3MnO₃ (LSMO) composites were investigated. The results of X-ray diffraction showed that the prepared BaTiO₃ powders were pure and fine, indicating that sintering temperature was effectively lowered when the NaCl sintering aid was added. X-ray diffraction patterns of \linebreak\noindent (1-x)BaTiO₃+(x)La_2/3Sr_1/3MnO₃ (LSMO) composites showed that LSMO and BaTiO₃ phases were coexistent and no other phases were detected. The impedance spectra showed that the resistance of grain boundaries for LSMO-doped samples was suppressed. The resistivity-temperature measurements showed that room-temperature resistivity of the composites was lowered from insulator for pure BaTiO₃ ceramic to 10³Ω•m for the x=0.3 sample. The sample of x≤0.2 showed the positive temperature coefficient (PTC) effect whereas the x=0.3 sample exhibited PTC effect at temperatures below 68 ℃ and then negative temperature coefficient (NTC) effect at temperatures above 68 ℃. The related mechanism has been elucidated.

Key words: Positive temperature coefficient, Composite, Impedance spectra, Resistivity