The atom is a basic unit of matter that consists of a dense central nucleus surrounded by a cloud of negatively charged electrons. The atomic nucleus contains a mix of positively charged protons and electrically neutral neutrons...
s and ion
An ion is an atom or molecule in which the total number of electrons is not equal to the total number of protons, giving it a net positive or negative electrical charge. The name was given by physicist Michael Faraday for the substances that allow a current to pass between electrodes in a...
s, which are bonded with each other with considerable interatomic forces, are not motionless. Due to the consistent vibrating movements, they are permanently deviating from their equilibrium position. Elastic wave
In physics, a wave is a disturbance that travels through space and time, accompanied by the transfer of energy.Waves travel and the wave motion transfers energy from one point to another, often with no permanent displacement of the particles of the medium—that is, with little or no associated mass...
s of different lengths, frequencies, and amplitudes run through crystalline solids at all times. The typical order of the atomic vibrations frequencies is 1013
Hz, and that of the amplitudes is 10-11
The process of the atomic vibrations is important for materials of different classes: for metallic, covalent, ionic crystals, semiconductors, intermetallic compounds, interstitial phases. The amplitude-frequency characteristics of the vibrating spectrum of an alloy can be varied, for example by alloying, to produce a well-directed effect on the properties of the materials.
The phenomena of atomic vibrations reflecting the interaction of micro-particles with each other depend on the deep properties of the medium. The vibrational amplitude and the vibrational
spectrum are determined by interatomic bonds.
The basic tool for the measurement of the mean-square amplitude of vibrations is the X-ray
X-radiation is a form of electromagnetic radiation. X-rays have a wavelength in the range of 0.01 to 10 nanometers, corresponding to frequencies in the range 30 petahertz to 30 exahertz and energies in the range 120 eV to 120 keV. They are shorter in wavelength than UV rays and longer than gamma...
diffraction. The heat vibrational motion of atoms, affecting the atom displacements, results in a weakining of diffracted lines (reflections). By measuring the intensity of the same reflections at two temperatures (for example, at a room and a high temperature) one can calculate mean-square amplitudes of the atom vibrations.
Correct data about the frequency spectrum is provided with the help of the technique of the neutron
The neutron is a subatomic hadron particle which has the symbol or , no net electric charge and a mass slightly larger than that of a proton. With the exception of hydrogen, nuclei of atoms consist of protons and neutrons, which are therefore collectively referred to as nucleons. The number of...
scattering by solids.