AC electrical conduction mechanisms and dielectrical studies of DD3 kaolin sintered at high temperature

In this study, DD3 kaolin, as a raw material, was thermally treated at a temperature ranging from 1000 °C to 1600 °C. The X-ray diffraction (XRD) patterns show the appearance of cristobalite and mullite phases at sintered temperature less than 1300 °C. Moreover, they revealed the formation of mullite at a higher temperature (1600 °C). The surface of mullite sample (DD3 at 1600 °C) is showed roughly with prismatic grains having an average size in the range of 32-42 nm. The FTIR spectrum is dominated by the stretching Si-O modes and Al-O at the wave number ranging from 443 to 1257 cm−1. The dielectric and electrical properties were investigated in a wide frequency (0.1-10 MHz) and at a temperature ranging from 0 to 200 °C. A strong dispersion of permittivity constants was observed at a low frequency, which can be attributed to interfacial Maxwell-Wagner-Sillar (MWS) relaxation. It is found that the ac conductivity depends on frequency and temperature with the Joncher power law A(T) ωs. Temperature analysis showed that the electron conductivity is controlled by both the small polaron tunneling (SPT) and the hopping correlated barrier (CBH) models.