Study on the microstructures and electrical properties of Bi0.5Ba0.5Fe0.5Ti0.49Nb0.01O3 thermistor ceramic

Abstract

The Bi0.5Ba0.5Fe0.5Ti0.49Nb0.01O3 thermistor has been prepared by the standard solid-state reaction method, and the microstructures, direct current resistivity, dielectric property, impedance and electric modulus were investigated by the X-ray diffraction, scanning electron microscopy, resistivity-temperature measurement and alternating current impedance spectroscopy. The results show that the material, with an average grain size of about 10 μm, still has cubic perovskite structure, and the lattice constant of the material becomes larger compared with that of the BaTiO3. The resistivity and thermistor contant B value of the material are about 107 Ω·cm and 7690 K, respectively, and the phase transition occurs twice (at 403 and 523 K), which are confirmed by the dielectric spectrum as a function of temperature. The complex impedance spectroscopy shows the non-ideal Debye type with two incomplete overlapping Cole-Cole semicircles corresponding to the grain and grain boundary resistance. The imaginary part of alternating current resistance as a function of frequency indicates there are two relaxation effects observable in the grain and grain boundary. The phase transition has little effect on the conduction property of bulk grain, but a great impact on that of the grain boundary.