Electrical properties of Sr xBa 1-xFe 0·6Sn 0·4O 3-ε NTC thermistors

Abstract

Polycrystalline thermistor ceramics with the stoichiometric formula, Sr xBa 1-xFe 0·6Sn 0·4O 3-ε (0·2 ≤ x ≤ 0·8), had been prepared by a standard solid state reaction route. X-ray diffraction analysis indicates that the ceramic system remains cubic perovskite structure with a very small lattice change. The electrical properties of Sr xBa 1-xFe 0·6Sn 0·4O 3-ε thermistors were studied using a digital thermometer over a wide range of 298-400 K. The thermistors showed an excellent negative temperature coefficient (NTC) thermistor behaviour. The values of resistivity at 298 K (ρ298), thermistor constant (B298/358) and activation energy (Ea) of the Sr xBa 1-xFe 0·6Sn 0·4O 3-ε thermistors, decreasing with the increase of Sr content, were in the range of 0·37-11·0 kΩ·cm, 2466-3703 K and 0·212-0·319 eV, respectively. For the thermistors with the compositions x = 0·2 and 0·4, the fitting equivalent circuit was composed of three RCPE elements corresponding to grain, grain boundary and ceramic-electrode interface, respectively. From the impedance plots, it was found that the fitting data showed good agreement with the experimental data. The extracted grain boundary resistance exhibited a NTC thermistor behaviour. © Indian Academy of Sciences.