Chapter 18: Electrical Properties

Electronic conduction in metals is explained through free electron and hole transport, where the density and mobility of charge carriers determine overall conductivity. The Fermi energy level defines the boundary of electron occupancy states, and thermal or photonic excitation generates mobile charge carriers. For metals, conductivity is limited by scattering events from lattice vibrations, impurities, and structural defects, principles unified by Matthiessen's rule. Semiconductors are classified into intrinsic materials like silicon and germanium and extrinsic types modified through doping, where donor impurities create n-type conduction through extra electrons and acceptor impurities produce p-type conduction through holes. The chapter traces temperature-dependent behavior through freeze-out, extrinsic, and intrinsic regimes, showing how carrier mobility decreases with increasing impurity concentration and thermal energy. The Hall effect provides experimental access to carrier type, concentration, and mobility. Practical semiconductor devices including p-n junction diodes function as rectifiers by conducting under forward bias and blocking under reverse bias, while transistors and metal-oxide-semiconductor field-effect transistors amplify and switch signals in microelectronic applications and flash memory systems. The text extends beyond semiconductors to cover ionic conduction in ceramic materials and electrical behavior in polymers, noting that conducting polymers achieve metallic conductivity when chemically doped, enabling battery and coating applications. Dielectric properties emerge from polarization mechanisms including electronic displacement, ionic displacement, and molecular orientation, with performance characterized by permittivity, dielectric constant, frequency response, loss, and breakdown strength. Ferroelectric materials like barium titanate display spontaneous polarization below their Curie temperature, while piezoelectric materials including lead zirconate titanate generate electrical charge under mechanical stress or deform under applied voltage, enabling applications in sensors, actuators, medical devices, and acoustic transducers.