3.6: Electronic Properties

Electronic band structure (or simply band structure) of a solid describes those ranges of energy that an electron within the solid may have (called energy bands, allowed bands, or simply bands) and ranges of energy that it may not have (called band gaps or forbidden bands). Band theory derives these bands and band gaps by examining the allowed quantum mechanical wave functions for an electron in a large, periodic lattice of atoms or molecules.

• 3.6.1: Ferroelectricity

  Ferroelectricity is a property observed in certain materials characterized by the presence of a spontaneous electric polarization without the presence of an electric field, much like how ferromagnetism is characterized by a spontaneous, permanent magnetic field. A subclass of piezoelectric and pyroelectric materials, ferroelectric materials are noncentrosymmetric crystals.

• 3.6.2: Hall Effect

  Hall Effect, deflection of conduction carriers by an external magnetic field, was discovered in 1879 by Edwin Hall.

• 3.6.3: Lattice Vibrations

  Almost all solids with the exception of amorphous solids and glasses have periodic arrays of atoms which form a crystal lattice. The existence of the periodic crystal lattice in solid materials provides a medium for characteristic vibrations. Between the lattice spacing, there are quantized vibrational modes called a phonon. The study of phonon is an important part of solid state physics.

• 3.6.4: Piezoelectricity

  Piezoelectricity is the effect of mechanical strain and electric fields on a material; mechanical strain on piezoelectric materials will produce a polarity in the material, and applying an electric field to a piezoelectric material will create strain within the material. When pressure is applied to a piezoelectric material, a dipole and net polarization are produced in the direction of the applied stress. Piezoelectricity has many application.

• 3.6.5: Resistivity

  Resistivity is the material property that pertains to how difficult it is for electrical current to flow through said material. Materials with high resistivity are known as insulators while materials with low resistivity are known as conductors. Spanning from 10-8 Ωm to 1020 Ωm, resistivity possess the largest range of values for any physical property. Resistivity is essential in many material applications including resistors, dielectrics, resistive heating, and superconducting.

• 3.6.6: Solving the Ultraviolet Catastrophe

  This is a very interesting story which first time lead people to believe that energies (associated with waves) are quantized rather than continuous. It all started with Black Body radiation when scientist attempted to explain the curve of frequency (or wavelength) vs intensity. Max Planck was first to explain the behavior in 1900, but no one accepted it; as there is no explanation for assuming energy corresponding to particular wavelength quantized rather than continuous.

• 3.6.7: Thermocouples

  This page provides a fundamental discussion of what a thermocouple is and how it works. A thermocouple is a temperature measuring device that can operate in a wide range of temperature. It is created by joining two dissimilar metal and/or semiconductor wires together. Thermocouples are inexpensive to make. However, they have limited accuracy.

• 3.6.8: Thermoelectrics

  Thermoelectrics (TEs) are materials that convert heat to electricity via the Seebeck effect. This unique ability of TEs is dependent upon electronic and thermal properties. The dimensionless figure of merit (zT) is used to quantify TE performance, and is related to the conversion efficiency (η). TEs optimizing energy conversion are currently used in radioisotope thermoelectric generators (RTGs) to generate electricity for spacecraft and other inaccessible power systems.