Electric Charge Transport and Dielectric Properties of the Barium Titanate Ceramics Obtained by Spark-Plasma Sintering with Different Carbon Content
Barium titanate (BaTiO3) ceramics with a different content of carbon were synthesized by spark-plasma sintering (SPS) at the temperature of 1100 C in vacuum under pressure. The concentration and distribution of carbon impurity inside the samples is estimated by scanning electron microscopy (SEM). The resistivity vs temperature and electric field dependences of the SPS ceramics with different carbon concentration have been studied. It is shown that their conduction is determined by the variable range hopping mechanism and obeys the Mott law. The density of localized states and localization radius of the electron wave function are determined. The difference in low-temperature resistivity of the SPS ceramics is caused by carbon concentration and connected with it variation of the dielectric permittivity. The relative dielectric permittivity of the SPS ceramics is colossal and reaches the values of 10^5 - 10^6 order. The larger carbon concentration is, the smaller the permittivity and resistivity are within the Mott hopping conduction temperature range. In the range from 250 K to 408 K one observes that the dielectric permittivity strongly increases forming a maximum in all samples, which may be related to the phase transition. Along with this, resistivity manifests a simultaneous sharp decrease. The decrease of resistivity along with the characteristic dependence of resistivity vs dielectric permittivity in the Mott conduction temperature range, evidences the validity of Heywang model for the description of SPS ceramics conduction mechanisms. The resistivity strongly decreases with increasing frequency in the AC regime, which agrees both with models of hopping conduction and effects based on the Maxwell-Wagner model. The studied SPS BaTiO3 ceramics are attractive for applications in energy storage and sensorics.