Phase component and conductivities of Co-doped BaTiO3 thermistors

BaTi1-x Co (x) O3-delta (0.01 a parts per thousand currency sign x a parts per thousand currency sign 0.4) ceramics were prepared by a wet chemical process polymerized with polyvinyl alcohol. The phases and related electrical properties of the ceramics were investigated. The phase component of the ceramics changes from a tetragonal phase to a hexagonal one with the Co concentration increase. A pure hexagonal phase formed in the ceramic with x = 0.2. The measurement of the temperature dependence of resistances revealed that the ceramic resistivities increase with temperature rising at the temperatures (T) lower than half of the related Debye temperature (I similar to(D)), and the ceramics show a negative temperature coefficient (NTC) effect at T > I similar to(D)/2. The material constants B (50/120) of the BaTi1-x Co (x) O3-I ' NTC thermistors were calculated to be 3,187, 2,968 and 2,648 K for x = 0.2, 0.3 and 0.4, respectively. Narrow-band conduction and non-adiabatic hopping models are proposed for the conduction mechanisms at T < I similar to(D)/2 and T > I similar to(D)/2, respectively.