Ionic conductivity
Encyclopedia
Ionic conduction is the movement of an ion
from one site to another through defect
s in the crystal lattice
of a solid. Ionic conduction is one aspect of current.
In solids, ions typically occupy fixed positions in the crystal lattice and do not move. However, ionic conduction can occur, especially as the temperature increases.
Ionic conduction is one of the mechanisms by which microwave oven
s are believed to work. Microwaves cause ions dissolved in the microwaved sample to oscillate
, colliding with neighboring molecules or atoms. These collisions cause agitation or motion, or heat. This mechanism is "important when considering the heating behavior of ionic liquid
s" within a microwave.
Ionic conduction in solids has been a subject of interest since the beginning of the 19th century. Michael Faraday
established in 1839 that the laws of electrolysis
are also obeyed in ionic solids like lead(II) fluoride
and silver sulfide
.
has extraordinary high ionic conductivity. While measuring conductivity, they found that above 147 °C, AgI changes into a phase that has an ionic conductivity of ~ 1 –1 cm−1, similar to that of its liquid phase. As a result, the high temperature phase of AgI was the first superionic conductor ever discovered. The highly conductive phase of AgI is now known as -AgI. It was shown that a sublattice
cationic disorder takes place in -AgI. The liquid-like state of Ag+ ions, as proposed by Strock (1934, 1936) and later reinforced by others (Geller, 1977; Funke, 1976), consists of a cubic unit cell of iodide ions (I-), in which a total of 42 sites (6 octahedral, 12 tetragonal and 24 trigonal bipyramidal) are available for 2 Ag+ ions, as shown in the Figure 1. O' Keeffe and Hyde (1976) have argued that this phase transition
in AgI is dramatic and powerful, nothing less than the melting and have also shown that the entropy
change at the superionic transition is comparable to its value at the melting. Thus, in the -phase, I− ions form a body-centered cubic
lattice and the Ag+ ions are distributed in such a way that 42 crystallographic
equivalent interstices
are available for the two Ag+ ions.
Alpha phase crystals of various materials like , , , etc. were soon discovered (Tubandt, 1932). By the early 1930s, it was demonstrated that these fast ionically conducting
solids could be treated entirely the same as aqueous electrolyte
s from the viewpoint of chemical reaction
s and thermodynamics
, hence these materials were labeled solid electrolytes.
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...
from one site to another through defect
Crystallographic defect
Crystalline solids exhibit a periodic crystal structure. The positions of atoms or molecules occur on repeating fixed distances, determined by the unit cell parameters. However, the arrangement of atom or molecules in most crystalline materials is not perfect...
s in the crystal lattice
Crystal structure
In mineralogy and crystallography, crystal structure is a unique arrangement of atoms or molecules in a crystalline liquid or solid. A crystal structure is composed of a pattern, a set of atoms arranged in a particular way, and a lattice exhibiting long-range order and symmetry...
of a solid. Ionic conduction is one aspect of current.
In solids, ions typically occupy fixed positions in the crystal lattice and do not move. However, ionic conduction can occur, especially as the temperature increases.
Ionic conduction is one of the mechanisms by which microwave oven
Microwave oven
A microwave oven is a kitchen appliance that heats food by dielectric heating, using microwave radiation to heat polarized molecules within the food...
s are believed to work. Microwaves cause ions dissolved in the microwaved sample to oscillate
Oscillation
Oscillation is the repetitive variation, typically in time, of some measure about a central value or between two or more different states. Familiar examples include a swinging pendulum and AC power. The term vibration is sometimes used more narrowly to mean a mechanical oscillation but sometimes...
, colliding with neighboring molecules or atoms. These collisions cause agitation or motion, or heat. This mechanism is "important when considering the heating behavior of ionic liquid
Ionic liquid
An ionic liquid is a salt in the liquid state. In some contexts, the term has been restricted to salts whose melting point is below some arbitrary temperature, such as . While ordinary liquids such as water and gasoline are predominantly made of electrically neutral molecules, ILs are largely made...
s" within a microwave.
Ionic conduction in solids has been a subject of interest since the beginning of the 19th century. Michael Faraday
Michael Faraday
Michael Faraday, FRS was an English chemist and physicist who contributed to the fields of electromagnetism and electrochemistry....
established in 1839 that the laws of electrolysis
Electrolysis
In chemistry and manufacturing, electrolysis is a method of using a direct electric current to drive an otherwise non-spontaneous chemical reaction...
are also obeyed in ionic solids like lead(II) fluoride
Lead(II) fluoride
Lead fluoride is a chemical compound that is an odorless white solid.Conditions/substances to avoid are: strong oxidizers.-Uses:Lead fluoride is used:* in low melting glasses* in glass coatings to reflect infrared rays...
and silver sulfide
Silver sulfide
Silver sulfide, Ag2S, is the sulfide of silver. This dense black solid constitutes the tarnish that forms over time on silverware and other silver objects. Silver sulfide is insoluble in all solvents, but is degraded by strong acids. Silver sulfide features a covalent bond, as it is made up of...
.
Silver iodide
In 1921, Tubandt et al. found that silver iodideSilver iodide
Silver iodide is a yellow, inorganic, photosensitive iodide of silver used in photography, in medicine as an antiseptic, and in rainmaking for cloud seeding.-Crystal structure:...
has extraordinary high ionic conductivity. While measuring conductivity, they found that above 147 °C, AgI changes into a phase that has an ionic conductivity of ~ 1 –1 cm−1, similar to that of its liquid phase. As a result, the high temperature phase of AgI was the first superionic conductor ever discovered. The highly conductive phase of AgI is now known as -AgI. It was shown that a sublattice
Crystal structure
In mineralogy and crystallography, crystal structure is a unique arrangement of atoms or molecules in a crystalline liquid or solid. A crystal structure is composed of a pattern, a set of atoms arranged in a particular way, and a lattice exhibiting long-range order and symmetry...
cationic disorder takes place in -AgI. The liquid-like state of Ag+ ions, as proposed by Strock (1934, 1936) and later reinforced by others (Geller, 1977; Funke, 1976), consists of a cubic unit cell of iodide ions (I-), in which a total of 42 sites (6 octahedral, 12 tetragonal and 24 trigonal bipyramidal) are available for 2 Ag+ ions, as shown in the Figure 1. O' Keeffe and Hyde (1976) have argued that this phase transition
Phase transition
A phase transition is the transformation of a thermodynamic system from one phase or state of matter to another.A phase of a thermodynamic system and the states of matter have uniform physical properties....
in AgI is dramatic and powerful, nothing less than the melting and have also shown that the entropy
Entropy
Entropy is a thermodynamic property that can be used to determine the energy available for useful work in a thermodynamic process, such as in energy conversion devices, engines, or machines. Such devices can only be driven by convertible energy, and have a theoretical maximum efficiency when...
change at the superionic transition is comparable to its value at the melting. Thus, in the -phase, I− ions form a body-centered cubic
Cubic crystal system
In crystallography, the cubic crystal system is a crystal system where the unit cell is in the shape of a cube. This is one of the most common and simplest shapes found in crystals and minerals....
lattice and the Ag+ ions are distributed in such a way that 42 crystallographic
Crystallography
Crystallography is the experimental science of the arrangement of atoms in solids. The word "crystallography" derives from the Greek words crystallon = cold drop / frozen drop, with its meaning extending to all solids with some degree of transparency, and grapho = write.Before the development of...
equivalent interstices
Interstitial
An interstitial space or interstice is an empty space or gap between spaces full of structure or matter.In particular, interstitial may refer to:-Physical sciences:...
are available for the two Ag+ ions.
Alpha phase crystals of various materials like , , , etc. were soon discovered (Tubandt, 1932). By the early 1930s, it was demonstrated that these fast ionically conducting
Fast ion conductor
In solid-state ionics, fast ion conductors, also known as solid electrolytes and superionic conductors, are materials that act as solid state ion conductors and are used primarily in solid oxide fuel cells. As solid electrolytes they conduct due to the movement of ions through voids, or empty...
solids could be treated entirely the same as aqueous electrolyte
Electrolyte
In chemistry, an electrolyte is any substance containing free ions that make the substance electrically conductive. The most typical electrolyte is an ionic solution, but molten electrolytes and solid electrolytes are also possible....
s from the viewpoint of chemical reaction
Chemical reaction
A chemical reaction is a process that leads to the transformation of one set of chemical substances to another. Chemical reactions can be either spontaneous, requiring no input of energy, or non-spontaneous, typically following the input of some type of energy, such as heat, light or electricity...
s and thermodynamics
Thermodynamics
Thermodynamics is a physical science that studies the effects on material bodies, and on radiation in regions of space, of transfer of heat and of work done on or by the bodies or radiation...
, hence these materials were labeled solid electrolytes.