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solid-state physics,study of the properties of bulk mattermatter,
anything that has mass and occupies space. Matter is sometimes called koinomatter (Gr. koinos=common) to distinguish it from antimatter, or matter composed of antiparticles.
..... Click the link for more information. rather than those of the individual particles that compose it. Solid-state physics is concerned with the properties exhibited by atoms and molecules because of their association and regular, periodic arrangement in crystalscrystal,
a solid body bounded by natural plane faces that are the external expression of a regular internal arrangement of constituent atoms, molecules, or ions. The formation of a crystal by a substance passing from a gas or liquid to a solid state, or going out of solution (by
..... Click the link for more information. . The descriptive side of the study of solids is crystallography. From a practical point of view, searches are made for new characteristics and behavior of various materials. The most spectacular discovery resulting from these searches has been the transistortransistor,
three-terminal, solid-state electronic device used for amplification and switching. It is the solid-state analog to the triode electron tube; the transistor has replaced the electron tube for virtually all common applications.
..... Click the link for more information. . From a theoretical point of view, attempts are made to predict and explain the nature of aggregates of atoms in terms of the basic laws of the quantum theoryquantum theory,
modern physical theory concerned with the emission and absorption of energy by matter and with the motion of material particles; the quantum theory and the theory of relativity together form the theoretical basis of modern physics.
..... Click the link for more information. and the well-understood properties of individual atoms. An important concern of solid-state physics is the mechanical and thermal behavior of solids; specific areas of study include the allowed vibration modes of crystals (see phononphonon
, quantum of vibrational energy. The atoms of any crystal are in a state of vibration, their average kinetic energy being measured by the absolute temperature of the crystal.
..... Click the link for more information. ), the transmission of vibrational energy (thermal conductivity), the amount of energy that must be absorbed to produce a given change in temperature (specific heatspecific heat,
ratio of the heat capacity of a substance to the heat capacity of a reference substance, usually water. Heat capacity is the amount of heat needed to change the temperature of a unit mass 1°.
..... Click the link for more information. ), and phase transitions such as the melting pointsmelting point,
temperature at which a substance changes its state from solid to liquid. Under standard atmospheric pressure different pure crystalline solids will each melt at a different specific temperature; thus melting point is a characteristic of a substance and can be used
..... Click the link for more information. of crystals. Although the crystalline, mechanical, thermal, and optical properties of solids are of great interest, it is the electrical properties that most clearly demarcate the various types of materials and which exhibit the greatest diversity of behavior. The single most important electrical characteristic of a solid is its electrical conductivity (the ease with which electric currents flow through it). See conductionconduction,
transfer of heat or electricity through a substance, resulting from a difference in temperature between different parts of the substance, in the case of heat, or from a difference in electric potential, in the case of electricity.
..... Click the link for more information. . Metals are highly conductive solids that offer little resistance to electric currents. Most solid nonmetals, on the other hand, are insulators (solids whose conductivity is nearly zero); they offer virtually infinite resistance to electric currents. A third class of solids possesses electrical conductivity that is neither very high nor very low; these solids are called semiconductorssemiconductor,
solid material whose electrical conductivity at room temperature is between that of a conductor and that of an insulator (see conduction; insulation). At high temperatures its conductivity approaches that of a metal, and at low temperatures it acts as an insulator.
..... Click the link for more information. . A principal triumph of quantum mechanics in solid-state physics is the explanation of these extreme variations of electrical conductivity in terms of the atomic structure of the three types of solids.
The study of the physical properties of solids, such as electrical, dielectric, elastic, and thermal properties, and their understanding in terms of fundamental physical laws. Most problems in solid-state physics would be called solid-state chemistry if studied by scientists with chemical training, and vice versa. Solid-state physics emphasizes the properties common to large classes of compounds rather than the dependence of properties upon compositions, the latter receiving greater emphasis in solid-state chemistry. In addition, solid-state chemistry tends to be more descriptive, while solid-state physics focuses upon quantitative relationships between properties and the underlying electronic structure.
Many of the scientists who study the physics of liquids identify with solid-state physics, and the term “condensed-matter physics” has been used by some researchers to replace “solid-state physics” as a division of physics. It includes noncrystalline solids such as glass as well as crystalline solids. See Amorphous solid
In solid-state physics it is generally assumed that the electronic states can be described as wavelike. The individual electronic states, called Bloch states, have energies which depend upon the wave number (a vector equal to the momentum divided by ℏ, which is Planck's constant divided by 2π), and the wave number is restricted to a domain called the Brillouin zone. This energy given as a function of the wave number is called the band structure. There are several curves, called bands, for each line in the Brillouin zone. See Brillouin zone
The total energy of a solid includes a sum of the energies of the occupied electronic states. Since the energy bands depend upon the positions of the atoms, so does the total energy, and the stable crystal structure is that which minimizes this energy. The theory has not proved adequate to really predict the crystal structure of various solids, but it is possible to predict the changes in energy under various distortions of the lattice. There are in fact three times as many independent distortions, called normal modes, as there are atoms in the solid. Each has a wave number, and the frequencies of the normal vibrational modes, as a function of wave number in the Brillouin zone, form vibrational bands in direct analogy with the electronic energy bands. These can be directly calculated from quantum theory or measured by using neutron or x-ray diffraction. See Crystal, Lattice vibrations, Neutron diffraction, X-ray diffraction