Om Parkash

Electronic ceramics are technological materials having a vast variety of applications such as actuators and sensors, computer memories, electrically controlled microwave tuning devices for RADAR, etc. and are playing key role in electronics industry today. An electronic ceramic component can be visualised as grain-grain boundary-electrode system. Impedance spectroscopy is being widely used to separate out contributions of these to the overall property of a ceramic. This involves equivalent circuit models. To facilitate development of suitable equivalent circuit models and obtain values of the components, some most useful circuits with their simulated behaviour are presented. Steps highly useful in the modelling process are summarised. The procedure of impedance spectroscopy is illustrated by analysing the impedance data of the ceramic system BaFexTi1-xO3 (x = 0.05) containing two phases.

Polymer ceramic composites are widely used for embedded capacitor application. In the present work PVDF has been used as a matrix and CCTO and LaCCTO have been used as reinforcement. Extrusion process has been used for the synthesis of composites. X-ray diffraction (XRD) patterns confirm the formation of single phase CCTO, and LaCCTO in its pure as well as composite state. It is found that La doping in CCTO considerably increases the dielectric constant and reduces the dielectric loss. A similar trend is observed in the composites with the increasing content of CCTO and LaCCTO.

PVDF has been reinforced with different amount of CaCu3Ti4-5x/4NbxO12 with powder prepared by solid state ceramic method. Composites were prepared by melt extrusion method. Phase composition was studied using powder X-ray diffraction (XRD). Microstructural, dielectric, and mechanical properties have also been studied. These composites have Young’s modulus more than that of pure PVDF. Two dielectric relaxations, one at low frequency and the other at high frequency, have been observed in these composites. Dielectric relaxation at low frequencies is of Maxwell-Wagner type while the one observed at high frequency is due to hopping of electrons among different valent states of transition metal ions. Nature of dielectric relaxation has been analysed using H-N function.

A series of ceria‐based nanocomposites consisting of lanthanum and strontium codoped ceria with composition Ce_0.89La_0.07Sr_0.04O_1.925 (CL7S4) and eutectic mixture of carbonates Li₂CO₃‐Na₂CO₃ (LNCO) have been prepared by mixing nanosize powders of CL7S4 and LNCO. Samples have been characterized using differential thermal analysis, X‐ray diffraction, scanning electron microscopy combined with energy‐dispersive spectroscopy, thermal expansion, and impedance spectroscopy. A sharp increase in ionic conductivity is observed in all the composite specimens corresponding to superionic transition. Sample containing 35 wt% of carbonate shows the maximum conductivity (2.56 × 10⁻¹ S/cm at 500°C) with activation energy of conduction, E_a 0.23 eV.