Polycrystalline silicon and zinc oxide ceramic are important electronic materials. The electrical properties which determine the applications of polycrystalline silicon in integrated circuits and solar cells and that of ZnO ceramic in varistors are due primarily to grain boundary effects in them. A large amount of information in this area has already been gathered in literature but the quantitative understanding of grain boundary effects in these materials is not yet complete. In this review the important aspects of grain boundaries and their effects on transport and photoelectric properties of polycrystalline silicon and on the I–V characteristic of ZnO varistors are discussed.

Conductivity (σ$_{ijk}$’s) measurement method is proposed to investigate dielectric relaxation in ternary polar–nonpolar mixture of N,N-dimethyl formamide (DMF)(j) with pyridine(k) or acetonitrile(k) dissolved in p-xylene (i) at various weight fractions (w$_{jk}$’s) and temperature under different bands (S, C, X and Ku) of microwave field applying Debye’s dielectric model. Ratio of slopes of imaginary σ$_{ijk}$″ vs. w$_{jk}$ with real σ$_{ijk}$′ vs. w$_{jk}$ of complex conductivity σ$_{ijk}$* as well as linear slope of σ$_{ijk}$″ vs. σ$_{ijk}$′ are used to predict τ$_{jk}$’s (relaxation time) and μ$_{jk}$’s (dipole moments). Variousmolecular associations are also identified from the meaningful interactions among polar–nonpolar molecules in terms of τ$_{jk}$ and μ$_{jk}$. Molecular dynamics or molecular environment surrounding the polar molecules DMF, pyridine or acetonitrileis extensively studied with the help of estimated thermodynamic energy parameters. The existence of Debye relaxation mechanism in polar–nonpolar mixture is authenticated by the estimated Debye factor. Microwave sensor development is also ascertained from various dielectric parameters like permittivity, conductivity and penetration depth under microwave field.