Dielectric and impedance properties of sintered magnesium aluminum silicate glass-ceramic

Magnesium aluminum silicate (MgO–Al₂O₃–SiO₂, MAS) glass-ceramic was prepared via sintering route. X-ray diffraction (XRD) analysis indicates the formation of multiphase compound with magnesium silicate fluoride and cordierite as major phases. Dielectric studies of the compound shows a strong frequency dispersion of permittivity in the low frequency region followed by a nearly frequency-independent behavior in the high frequency region. The presence of alkali ions (K⁺) in MAS glass-ceramic results in higher dielectric constant and higher losses. Dielectric loss (tanδ) seems to be reduced at higher frequencies after reaching the instrumental saturation at 1 kHz. Electrical properties of the material have been studied using a complex impedance spectroscopy (CIS) technique in a wide temperature (30–500 ℃) and frequency (100 Hz–5 MHz) ranges. The complex impedance plots reveal the contribution of bulk as well as grain boundary effects in it. The bulk resistance, evaluated from complex impedance spectrum, has been observed to decrease with the rise in temperature, showing a typical negative temperature coefficient of resistance (NTCR) behavior. The smaller activation energy (E_a) of the compound within moderate temperature range suggests the presence of ions (K⁺ and F^-) and singly ionized oxygen vacancies in the conduction process. The nature of variation of the electrical conductivity, and the values of activation energy of different temperature regions, suggest that the conduction process is of mixed type.