Relationships between microstructure and electrical properties of liquid-phase sintered silicon carbide materials using impedance spectroscopy

A range of liquid-phase sintered silicon carbide (LPS SiC) materials were produced, using hot pressing and gas pressure sintering. The densified materials were further heat-treated at the sintering temperature, 1925 °C. The ac electrical properties were measured and impedance spectroscopy used between room temperature and 330 °C. The investigated LPS SiC materials could be classified into three groups, with different electrical properties, which could be related to the grain boundary phases present in the materials. The temperature dependence of the log of the dc conductivity of hot pressed (HP) and gas pressure sintered (GPS) materials, 1/T0.25, showed that the conduction mechanism in these LPS SiC materials was variable range hopping conduction of electrons between defect sites. This non-Arrhenius behaviour showed that SiC did not contribute to the impedance spectra, which could be shown to be due to the aluminates and silicates that are known to be present from XRD results.