EVIDENCE OF 2 FERROELECTRIC PTCR COMPONENTS IN VALENCE-COMPENSATED CERAMIC SYSTEM BA1-XLAXTI1-XCOXO3

The electrical behaviour of valence-compensated ceramic system Ba1-xLa x Ti1-xCoxO3 has been studied as a function of temperature (300-600 K) and composition (x less than or equal to 0.20), using the method of i mpedance spectroscopy. The necessary equivalent circuit models that re present the data best have been obtained using impedance and modulus f ormalisms and grain and grain boundary contributions have been separat ed out. The compositions x = 0.20 and 0.10 show a negative temperature coefficient of resistance (NTCR) behaviour whereas a very small varia tion of the grain and grain boundary resistance with temperature is ob served for x = 0.05. A positive temperature coefficient of resistance (PTCR) behaviour having two ferroelectric components is observed for x = 0.01. These results reveal limitations in current theories of the P TCR effect.