Classical and quantum conductivity

Classical and quantum mechanical views of conductivity have both described the movements of electrons in a metallic solid. The free electron gas that is present in metallic solids is the reason for an important property of all metals: conductivity. This article will discuss the theory of conduction, specifically the theory of classical conduction whose defects were explained by the quantum theory. The modifications that the quantum theory adds to classical conduction not only explain the flaws that arose in the classical theory, but add a new perspective on conduction that is a current subject of physics research.

The advent of quantum mechanics allowed a greater understanding of the physical properties of solids. Solids can be split into two groups: amorphous and crystalline. Amorphous solid structures occur when a liquid is cooled too rapidly for the crystalline structure to form, for example glass. In a crystalline structure, several different types of bonding are possible, including ionic, covalent, and metallic. These, along with the sizes of the atoms, determine the crystal's structure.

Ionic crystals can form in as many as fourteen different shapes. For example, in the face-centered cubic structure, the crystal’s unit cell is a cube, with the smaller of the two ions occupying the center of each face. In the body-centered cubic structure, eight of the larger ions form a cubic shape, while one of the smaller ions occupies its center. A hexagonal close-packed crystal structure is obtained by stacking identical spheres, and fitting these stacks into the triangular depressions of adjacent stacks.

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