Off-center
ion
An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by convent ...
s in
crystal
A crystal or crystalline solid is a solid material whose constituents (such as atoms, molecules, or ions) are arranged in a highly ordered microscopic structure, forming a crystal lattice that extends in all directions. In addition, macros ...
s are
substitutional impurity ions whose equilibrium position is shifted away from the regular
lattice
Lattice may refer to:
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* Latticework, an ornamental criss-crossed framework, an arrangement of crossing laths or other thin strips of material
* Lattice (music), an organized grid model of pitch ratios
* Lattice (pastry), an or ...
site. The magnitude of the shift typically ranges from 0.2 to 1.0 Å. There are two possible mechanisms that can cause impurity ion displacement. If the impurity ion is smaller than the regular ion (by 10% or more), the displacement arises because the repulsive forces between the impurity ion and its nearest neighbors stabilizing the ion at the regular site are strongly weakened. If the impurity ion is bigger than the regular ion, the displacement arises because of different covalency of the chemical bonds with the nearest neighbors for the impurity and regular ions.
Off-center position of
substitutional ions was first discovered in lithium-doped
KCl
KCL or KCl may refer to:
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* Potassium chloride (KCl), a metal halide salt
* Keycode lookup, keycode log, or keycode list
* Kirchhoff's current law, in physics
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Other uses
...
by two groups of American physicists in 1965.
Since these pioneer works crystals with off-center impurity ions have attracted continuous attention. The cause of such interest is that these crystals can be used as good model objects for the investigation of such key phenomena in
solid state physics
Solid-state physics is the study of rigid matter, or solids, through methods such as solid-state chemistry, quantum mechanics, crystallography, electromagnetism, and metallurgy. It is the largest branch of condensed matter physics. Solid-state p ...
as
quantum tunnelling
In physics, quantum tunnelling, barrier penetration, or simply tunnelling is a quantum mechanical phenomenon in which an object such as an electron or atom passes through a potential energy barrier that, according to classical mechanics, shoul ...
of atomic particles in solid state, cooperative properties of the system of local centers with internal degrees of freedom, and
ferroelectricity
In physics and materials science, ferroelectricity is a characteristic of certain materials that have a spontaneous electric polarization that can be reversed by the application of an external electric field. All ferroelectrics are also piezoel ...
.
References
{{reflist
External links
I.F. Ioffe Physical Technical Institute (St.-Petersburg, Russia) website.
Solid-state chemistry