Structural, micro-structural, optical and dielectric behavior of mullite ceramics

Mullite ceramics of two different compositions Al0.60Si0.40O and Al0.75Si0.25O have been synthesized by pyrophoric method followed by reaction sintering at 1050 degrees C. The structural, micro-structural, optical, and dielectric characterization of mullite has been carried out through XRD, Raman, SEM, UV-Visible and dielectric studies. In this work, the synthesized mullite materials possess quite high dielectric constant value with negligible dielectric loss factor. The room temperature dielectric constant values for Al0.60Si0.40O and Al0.75Si0.25O stoichiometric mullites are found to be 110 and 2665 with a loss factor of 2.04 and 2.29 at 100 Hz frequency, which is comparatively high than the corresponding values of dielectric constants reported in previous literatures of mullite. The dielectric constant values for both the ceramics are very high (>104) for temperatures greater than 250 degrees C. The room temperature dielectric constant (6.03 and 5.08, at 1 MHz), dielectric loss (0.07 and 0.05, at 1 MHz), electrical conductivity (1.5 x 10-5 S/m and 8.1 x 10-6 S/m, at 300 degrees C) results for Al0.60Si0.40O and Al0.75Si0.25O prove these ceramics suitable for electronics-related applications. The Arrhenius type conductivity, non-Debye type relaxation mechanism is confirmed from AC conductivity, complex impedance, and modulus study of these ceramics. These ceramics possess high optical band gap values of 3.46 eV and 3.36 eV for Al0.60Si0.40O and Al0.75Si0.25O, respectively which is suitable for using as electronic circuit packaging material or as a dielectric substrate material for any kind of storage devices.