Physics, Solid-State

Crystals and Crystallography

The bulk of solid-state physics, viewed mostly as general theory, is extensively focused on crystals. Crystalline materials are solids with a highly organized atomic structure typically based on a regular repeated pattern. Most solids that are known happen to be crystalline. There are also some known liquid crystalline colloids of the nanoparticles. Much more progress has been effectively made in first decades of the 21st century to understand the behavior of these crystalline solids rather than that of the noncrystalline materials, since most of the concerned calculations are easier to perform on crystalline materials. Understanding the basic electrical properties of these solids is of pivotal importance to modern-day society and advancing technology.

Primarily, this phenomenon is because of the periodicity exhibited by the atoms in a crystal—its defining characteristic, which greatly facilitates mathematical modeling. Similarly, crystalline materials quite often have magnetic, electrical, mechanical, or optical properties which can be exploited for the purposes of engineering. The typical forces that exist between the constituent atoms in a crystal can take a variety of structural forms. For example, a crystal of sodium chloride (i.e., common salt) is basically made up of sodium and chloride ions, which are held together with many ionic bonds. Sodium chloride specifically crystallizes in the form of a cubic lattice, but with a very different unit cell. The structure of sodium chloride consists of exactly equal numbers of both sodium and chlorine ions, stringently placed at every alternate point of a very simple cubic lattice. In contrast, the noble gases (helium, neon, argon, krypton, xenon, and the radioactive radon) never undergo any of these typical types of bonding. In solid form, all the noble gases are actually held together with the Van der Waals forces acting between them, resulting from the total polarization of the surrounding electronic charge cloud on each of these atoms. The actual difference that exists between the types of solid typically result from the fundamental differences between their intimate bonding. Many properties of these solid [Page 728]materials are vastly affected by their crystal structure. This structure can be effectively investigated using a wide range of various crystallographic techniques including neutron diffraction, X-ray crystallography, and electron diffraction. Various diffraction techniques solely exploit the phenomenon of scattering of radiation from a large number of available sites. There are various diffraction techniques which are currently being employed that result in typical diffraction patterns. These typical patterns are gross records of the various diffracted beams produced. The sizes of individual crystals found inside a crystalline solid material do vary extensively depending on the type of material involved and the prevalent conditions when the material was formed. Most of the crystalline materials encountered in everyday life are by nature polycrystalline, with the individual crystals being microscopic in scale, but macroscopic single crystals can also be very easily produced either by natural (e.g., diamonds) or artificial methods.

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