Electrical properties of hexagonal BaTi0.8Co0.2O3-δ ceramic with NTC effect

The structure and electrical properties of BaTi0.8Co0.2O3-δ ceramic prepared by a wet chemical process polymerized with polyvinyl alcohol were investigated. The crystal structure of BaTi0.8Co0.2O3-δ was determined to be a hexagonal phase. The measurements of temperature dependence of resistivity revealed that the ceramic has the characteristic of negative temperature coefficient (NTC) of resistivity. The electrical properties analysed by impedance and electrical modulus spectroscopies showed that the grains play a major role in electrical properties, compared with the grain boundaries. The co-existence of the overlapping and separation between the frequency dependence plots of the normalized imaginary part of impedance (Z''/Z''max) and electric modulus (M''/M''max) peaks is observed. The conduction mechanisms combining the hopping model and band conduction are proposed for the NTC effect in the BaTi0.8Co0.2O3-δ thermistor.