Solid-state ionics is the study of ionic-electronic mixed conductor and fully ionic conductors ( solid electrolytes) and their uses. Some materials that fall into this category include inorganic crystalline and polycrystalline solids, ceramics, glasses, polymers, and composites. Solid-state ionic devices, such as

solid oxide fuel cell A solid oxide fuel cell (or SOFC) is an electrochemical conversion device that produces electricity directly from oxidizing a fuel. Fuel cells are characterized by their electrolyte material; the SOFC has a solid oxide or ceramic electrolyte. A ...

s, can be much more reliable and long-lasting, especially under harsh conditions, than comparable devices with fluid electrolytes. The field of solid-state ionics was first developed in Europe, starting with the work of

Michael Faraday Michael Faraday (; 22 September 1791 – 25 August 1867) was an English scientist who contributed to the study of electromagnetism and electrochemistry. His main discoveries include the principles underlying electromagnetic inducti ...

on solid electrolytes Ag₂S and PbF₂ in 1834. Fundamental contributions were later made by

Walther Nernst Walther Hermann Nernst (; 25 June 1864 – 18 November 1941) was a German chemist known for his work in thermodynamics, physical chemistry, electrochemistry, and solid state physics. His formulation of the Nernst heat theorem helped pave the wa ...

, who derived the

Nernst equation In electrochemistry, the Nernst equation is a Thermodynamics#Chemical thermodynamics, chemical thermodynamical relationship that permits the calculation of the reduction potential of a reaction (half-cell or electrochemical cell, full cell reacti ...

and detected ionic conduction in heterovalently doped

zirconia Zirconium dioxide (), sometimes known as zirconia (not to be confused with zircon), is a white crystalline oxide of zirconium. Its most naturally occurring form, with a monoclinic crystalline structure, is the mineral baddeleyite. A dopant stabi ...

, which he applied in his

Nernst lamp The Nernst lamp was an early form of incandescent lamp. Construction Nernst lamps did not use a glowing tungsten filament. Instead, they used a ceramic rod that was heated to incandescence. Because the rod (unlike tungsten wire) would not ...

. Another major step forward was the characterization of

silver iodide Silver iodide is an inorganic compound with the formula Ag I. The compound is a bright yellow solid, but samples almost always contain impurities of metallic silver that give a gray coloration. The silver contamination arises because AgI is hig ...

in 1914. Around 1930, the concept of point defects was established by

Yakov Frenkel __NOTOC__ Yakov Il'ich Frenkel (russian: Яков Ильич Френкель; 10 February 1894 – 23 January 1952) was a Soviet physicist renowned for his works in the field of condensed matter physics. He is also known as Jacov Frenkel, frequ ...

Walter Schottky Walter Hans Schottky (23 July 1886 – 4 March 1976) was a German physicist who played a major early role in developing the theory of electron and ion emission phenomena, invented the screen-grid vacuum tube in 1915 while working at Siemens, ...

and

Carl Wagner Carl Wilhelm Wagner (May 25, 1901 – December 10, 1977) was a German Physical chemist. He is best known for his pioneering work on Solid-state chemistry, where his work on oxidation rate theory, counter diffusion of ions and defect chemistry ...

, including the development of point-defect

thermodynamics Thermodynamics is a branch of physics that deals with heat, work, and temperature, and their relation to energy, entropy, and the physical properties of matter and radiation. The behavior of these quantities is governed by the four laws of the ...

by Schottky and Wagner; this helped explain ionic and electronic transport in ionic crystals, ion-conducting glasses, polymer electrolytes and nanocomposites. In the late 20th and early 21st centuries, solid-state ionics focused on the synthesis and characterization of novel solid electrolytes and their applications in solid state battery systems,

fuel cell A fuel cell is an electrochemical cell that converts the chemical energy of a fuel (often hydrogen) and an oxidizing agent (often oxygen) into electricity through a pair of redox reactions. Fuel cells are different from most batteries in requ ...

s and sensors. The term ''solid state ionics'' was coined in 1967 by Takehiko Takahashi, but did not become widely used until the 1980s, with the emergence of the journal ''

Solid State Ionics Solid-state ionics is the study of ionic-electronic mixed conductor and fully ionic conductors ( solid electrolytes) and their uses. Some materials that fall into this category include inorganic crystalline and polycrystalline solids, ceramics, g ...

''. The first international conference on this topic was held in 1972 in

Belgirate Belgirate is a ''comune'' (municipality) in the Province of Verbano-Cusio-Ossola in the Italian region of Piedmont, located about northeast of Turin and about south of Verbania. Belgirate borders the following municipalities: Besozzo, Brebbia, ...

, Italy, under the name "Fast Ion Transport in Solids, Solid State Batteries and Devices".

History

Foundations

In the early 1830s, Michael Faraday laid the foundations of electrochemistry and solid-state ionics by discovering the motion of ions in liquid and solid electrolytes. Earlier, around 1800,

Alessandro Volta Alessandro Giuseppe Antonio Anastasio Volta (, ; 18 February 1745 – 5 March 1827) was an Italian physicist, chemist and lay Catholic who was a pioneer of electricity and power who is credited as the inventor of the electric battery and the ...

used a liquid electrolyte in his

voltaic pile upright=1.2, Schematic diagram of a copper–zinc voltaic pile. The copper and zinc discs were separated by cardboard or felt spacers soaked in salt water (the electrolyte). Volta's original piles contained an additional zinc disk at the bottom, ...

, the first electrochemical battery, but failed to realize that ions are involved in the process. Meanwhile, in his work on decomposition of solutions by electric current, Faraday used not only the ideas of

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 conve ...

cation 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 ...

anion 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 ...

electrode An electrode is an electrical conductor used to make contact with a nonmetallic part of a circuit (e.g. a semiconductor, an electrolyte, a vacuum or air). Electrodes are essential parts of batteries that can consist of a variety of materials de ...

anode An anode is an electrode of a polarized electrical device through which conventional current enters the device. This contrasts with a cathode, an electrode of the device through which conventional current leaves the device. A common mnemonic is ...

cathode A cathode is the electrode from which a conventional current leaves a polarized electrical device. This definition can be recalled by using the mnemonic ''CCD'' for ''Cathode Current Departs''. A conventional current describes the direction in whi ...

electrolyte An electrolyte is a medium containing ions that is electrically conducting through the movement of those ions, but not conducting electrons. This includes most soluble salts, acids, and bases dissolved in a polar solvent, such as water. Upon dis ...

and

electrolysis In chemistry and manufacturing, electrolysis is a technique that uses direct electric current (DC) to drive an otherwise non-spontaneous chemical reaction. Electrolysis is commercially important as a stage in the separation of elements from n ...

, but even the present-day terms for them.See and other OED pages for the etymology of these terms Faraday associated electric current in an electrolyte with the motion of ions, and discovered that ions can exchange their charges with an electrode while they were transformed into elements by electrolysis. He quantified those processes by two laws of electrolysis. The first law (1832) stated that the mass of a product at the electrode, Δm, increases linearly with the amount of charge passed through the electrolyte, Δq. The second law (1833) established the proportionality between Δm and the “electrochemical equivalent” and defined the

Faraday constant In physical chemistry, the Faraday constant, denoted by the symbol and sometimes stylized as ℱ, is the electric charge per mole of elementary charges. It is named after the English scientist Michael Faraday. Since the 2019 redefinition of S ...

F as F = (Δq/Δm)(M/z), where M is the molar mass and z is the charge of the ion. In 1834, Faraday discovered ionic conductivity in heated solid electrolytes Ag₂S and PbF₂. In PbF₂, the conductivity increase upon heating was not sudden, but spread over a hundred degrees Celsius. Such behavior, called Faraday transition, is observed in the cation conductors Na₂S and Li₄SiO₄ and anion conductors PbF₂, CaF₂, SrF₂, SrCl₂ and LaF₃. Later in 1891,

Johann Wilhelm Hittorf Johann Wilhelm Hittorf (27 March 1824 – 28 November 1914) was a German physicist who was born in Bonn and died in Münster, Germany. Hittorf was the first to compute the electricity-carrying capacity of charged atoms and molecules (ions), an ...

reported on the

ion transport number In chemistry, ion transport number, also called the transference number, is the fraction of the total electric current carried in an electrolyte by a given ionic species : :t_i = \frac Differences in transport number arise from differences in el ...

s in electrochemical cells, and in the early 20th century those numbers were determined for solid electrolytes.

First theories and applications

The

stimulated a series of improved batteries, such as the

Daniell cell The Daniell cell is a type of electrochemical cell invented in 1836 by John Frederic Daniell, a British chemist and meteorologist, and consists of a copper pot filled with a copper (II) sulfate solution, in which is immersed an unglazed earthenw ...

and

lead acid battery Lead is a chemical element with the symbol Pb (from the Latin ) and atomic number 82. It is a heavy metal that is denser than most common materials. Lead is soft and malleable, and also has a relatively low melting point. When freshly cut, le ...

. Their operation was largely understood in the late 1800s from the theories by

Wilhelm Ostwald Friedrich Wilhelm Ostwald (; 4 April 1932) was a Baltic German chemist and German philosophy, philosopher. Ostwald is credited with being one of the founders of the field of physical chemistry, with Jacobus Henricus van 't Hoff, Walther Nernst, ...

and

. In 1894 Ostwald explained the energy conversion in a fuel cell and stressed that its efficiency was not limited by

. Ostwald, together with Jacobus Henricus van 't Hoff, and

Svante Arrhenius Svante August Arrhenius ( , ; 19 February 1859 – 2 October 1927) was a Swedes, Swedish scientist. Originally a physicist, but often referred to as a chemist, Arrhenius was one of the founders of the science of physical chemistry. He received ...

, was a founding father of electrochemistry and chemical ionic theory, and received a Nobel prize in chemistry in 1909. His work was continued by Walther Nernst, who derived the

and described ionic conduction in heterovalently doped

, which he used in his

. Nernst was inspired by the dissociation theory of Arrhenius published in 1887, which relied on ions in solution. In 1889 he realized the similarity between electrochemical and chemical equilibria, and formulated his famous equation that correctly predicted the output voltage of various electrochemical cells based on liquid electrolytes from the thermodynamic properties of their components. Besides his theoretical work, in 1897 Nernst patented the first lamp that used a solid electrolyte. Contrary to the existing carbon-filament lamps, Nernst lamp could operate in air and was twice more efficient as its emission spectrum was closer to that of daylight. AEG, a lighting company in Berlin, bought the Nernst’s patent for one million

German gold mark The German mark (german: Goldmark ; sign: ℳ) was the currency of the German Empire, which spanned from 1871 to 1918. The mark was paired with the minor unit of the pfennig (₰); 100 pfennigs were equivalent to 1 mark. The mark was on the g ...

s, which was a fortune at the time, and used 800 of Nernst lamps to illuminate their booth at the world’s fair

Exposition Universelle (1900) The Exposition Universelle of 1900, better known in English as the 1900 Paris Exposition, was a world's fair held in Paris, France, from 14 April to 12 November 1900, to celebrate the achievements of the past century and to accelerate developmen ...

Ionic conductivity in silver halides

Among several solid electrolytes described in the 19th and early 20th century, α-AgI, the high-temperature crystalline form of silver iodide, is widely regarded as the most important one. Its electrical conduction was characterized by Carl Tubandt and E. Lorenz in 1914. Their comparative study of AgI, AgCl and AgBr demonstrated that α-AgI, is thermally stable and highly conductive between 147 and 555 °C; the conductivity weakly increased with temperature in this range and then dropped upon melting. This behavior was fully reversible and excluded non-equilibrium effects. Tubandt and Lorenz described other materials with a similar behavior, such as α-CuI, α-CuBr, β-CuBr, and high-temperature phases of Ag₂S, Ag₂Se and Ag₂Te. They associated the conductivity with cations in silver and cuprous halides and with ions and electrons in silver chalcogenides.

Point defects in ionic crystals

In 1926,

suggested that in an ionic crystal like AgI, in thermodynamic equilibrium, a small fraction of the cations, α, are displaced from their regular lattice sites into interstitial positions. He related α with the

Gibbs energy In thermodynamics, the Gibbs free energy (or Gibbs energy; symbol G) is a thermodynamic potential that can be used to calculate the maximum amount of work (physics), work that may be performed by a closed system, thermodynamically closed system a ...

for the formation of one mol of Frenkel pairs, ΔG, as α = exp(-ΔG/2RT), where T is temperature and R is the

gas constant The molar gas constant (also known as the gas constant, universal gas constant, or ideal gas constant) is denoted by the symbol or . It is the molar equivalent to the Boltzmann constant, expressed in units of energy per temperature increment per ...

; for a typical value of ΔG = 100 kJ/mol, α ~ 1 at 100 °C and ~6 at 400 °C. This idea naturally explained the presence of an appreciable fraction of mobile ions in otherwise defect-free ionic crystals, and thus the ionic conductivity in them. Frenkel’s idea was expanded by

and

in their 1929 theory, which described the equilibrium thermodynamics of point defects in ionic crystals. In particular, Wagner and Schottky related the deviations from

stoichiometry Stoichiometry refers to the relationship between the quantities of reactants and products before, during, and following chemical reactions. Stoichiometry is founded on the law of conservation of mass where the total mass of the reactants equal ...

in those crystals with the

chemical potential In thermodynamics, the chemical potential of a species is the energy that can be absorbed or released due to a change of the particle number of the given species, e.g. in a chemical reaction or phase transition. The chemical potential of a species ...

s of the crystal components, and explained the phenomenon of mixed electronic and ionic conduction. Wagner and Schottky considered four extreme cases of point-defect disorder in a stoichiometric binary ionic crystal of type AB: # Pairs of interstitial cations A⁺ and lattice vacancies (Frenkel defects) #Pairs of interstitial anions B⁻ and lattice vacancies (anti-Frenkel defects) #Pairs of interstitial cations A⁺ and interstitial anions B⁻ with no vacancies # Pairs of A and B-type lattice vacancies with no interstitials (Schottky disorder). Type-3 disorder does not occur in practice, and type 2 is observed only in rare cases when anions are smaller than cations, while both types 1 and 4 are common and show the same exp(-ΔG/2RT) temperature dependence. Later in 1933, Wagner suggested that in metal oxides an excess of metal would result in extra electrons, while a deficit of metal would produce electron holes, i.e., that atomic non-stoichiometry would result in a mixed ionic-electronic conduction.

Other types of disorder

Ionic glasses

The studies of crystalline ionic conductors where excess ions were provided by point defect continued through 1950s, and the specific mechanism of conduction was established for each compound depending on its ionic structure. The emergence of glassy and polymeric electrolytes in the late 1970s provided new ionic conduction mechanisms. A relatively wide range of conductivites was attained in glasses, wherein mobile ions were dynamically decoupled from the matrix. It was found that the conductivity could be increased by doping a glass with certain salts, or by using a glass mixture. The conductivity values could be as high as 0.03 S/cm at room temperature, with activation energies as low as 20 kJ/mol. Compared to crystals, glasses have

isotropic Isotropy is uniformity in all orientations; it is derived . Precise definitions depend on the subject area. Exceptions, or inequalities, are frequently indicated by the prefix ' or ', hence ''anisotropy''. ''Anisotropy'' is also used to describe ...

properties, continuously tunable composition and good workability; they lack the detrimental

grain boundaries In materials science, a grain boundary is the interface between two grains, or crystallites, in a polycrystalline material. Grain boundaries are two-dimensional crystallographic defect, defects in the crystal structure, and tend to decrease the ...

and can be molded into any shape, but understanding their ionic transport was complicated by the lack of long-range order. Historically, an evidence for ionic conductivity was provided back in the 1880s, when German scientists noticed that a well-calibrated thermometer made of Thuringian glass would show −0.5 °C instead of 0 °C when placed in ice shortly after immersion in boiling water, and recover only after several months. In 1883, they reduced this effect 10 times by replacing a mixture of sodium and potassium in the glass by either sodium or potassium. This finding helped

Otto Schott Friedrich Otto Schott (1851–1935) was a German chemist, glass technologist, and the inventor of borosilicate glass. Schott systematically investigated the relationship between the chemical composition of the glass and its properties. In this wa ...

develop the first accurate lithium-based thermometer. More systematic studies on ionic conductivity in glass appeared in 1884, but received broad attention only a century later. Several universal laws have been empirically formulated for ionic glasses and extended to other ionic conductors, such as the frequency dependence of electrical conductivity σ(ν) – σ(0) ~ ν^p, where the exponent p depends on the material, but not on temperature, at least below ~100 K. This behavior is a fingerprint of activated hopping conduction among nearby sites.

Polymer electrolytes

In 1975, Peter V. Wright, a polymer chemist from Sheffield (UK), produced the first polymer electrolyte, which contained sodium and potassium salts in a

polyethylene oxide Polyethylene glycol (PEG; ) is a polyether compound derived from petroleum with many applications, from industrial manufacturing to medicine. PEG is also known as polyethylene oxide (PEO) or polyoxyethylene (POE), depending on its molecular we ...

(PEO) matrix. Later another type of polymer electrolytes,

polyelectrolyte Polyelectrolytes are polymers whose repeating units bear an electrolyte group. Ion#Anions and cations, Polycations and polyanions are polyelectrolytes. These groups dissociation (chemistry), dissociate in aqueous solutions (water), making the pol ...

, was put forward, where ions moved through an electrically charged, rather than neutral, polymer matrix. Polymer electrolytes showed lower conductivities than glasses, but they were cheaper, much more flexible and could be easier machined and shaped into various forms. While ionic glasses are typically operated below, polymer conductors are typically heated above their

glass transition The glass–liquid transition, or glass transition, is the gradual and reversible transition in amorphous materials (or in amorphous regions within semicrystalline materials) from a hard and relatively brittle "glassy" state into a viscous or rubb ...

temperatures. Consequently, both the electric field and mechanical deformation decay on a similar time scale in polymers, but not in glasses. Between 1983 and 2001 it was believed that the amorphous fraction is responsible for ionic conductivity, i.e., that (nearly) complete structural disorder is essential for the fast ionic transport in polymers. However, a number of crystalline polymers have been described in 2001 and later with ionic conductivity as high as 0.01 S/cm 30 °C and activation energy of only 0.24 eV.

Nanostructures

In the 1970s–80s, it was realized that nanosized systems may affect ionic conductivity, opening a new field of

nanoionics Nanoionics is the study and application of phenomena, properties, effects, methods and mechanisms of processes connected with fast ion transport (FIT) in all-solid-state nanoscale systems. The topics of interest include fundamental properties of ...

. In 1973, it was reported that ionic conductivity of

lithium iodide Lithium iodide, or LiI, is a compound of lithium and iodine. When exposed to air, it becomes yellow in color, due to the oxidation of iodide to iodine. It crystallizes in the NaCl motif. It can participate in various hydrates.Wietelmann, Ulrich an ...

(LiI) crystals could be increased 50 times by adding to it a fine powder of ‘’insulating’’ material (alumina). This effect was reproduced in the 1980s in Ag- and Tl-halides doped with alumina nanoparticles. Similarly, addition of insulating nanoparticles helped increase the conductivity of ionic polymers. These unexpected results were explained by charge separation at the matrix-nanoparticle interface that provided additional conductive channels to the matrix, and the small size of the filler particles was required to increase the area of this interface. Similar charge-separation effects were observed for grain boundaries in crystalline ionic conductors.

Applications

By 1971, solid-state cells and batteries based on

rubidium silver iodide Rubidium silver iodide is a ternary compound, ternary inorganic compound with the formula RbAg4I5. Its conductivity involves the movement of silver ions within the crystal lattice. It was discovered while searching for chemicals which had the Ionic ...

(RbAg₄I₅) have been designed and tested in a wide range of temperatures and discharge currents. Despite the relatively high conductivity of RbAg₄I₅, they have never been commercialized due to a low overall energy content per unit weight (ca. 5 W·h/kg). On the contrary, LiI, which had a conductivity of only ca. 1 S/cm at room temperature, found a wide-scale application in batteries for

artificial pacemaker An artificial cardiac pacemaker (or artificial pacemaker, so as not to be confused with the natural cardiac pacemaker) or pacemaker is a medical device that generates electrical impulses delivered by electrodes to the chambers of the heart eith ...

s. The first such device, based on undoped LiI, was implanted into a human in March 1972 in

Ferrara Ferrara (, ; egl, Fràra ) is a city and ''comune'' in Emilia-Romagna, northern Italy, capital of the Province of Ferrara. it had 132,009 inhabitants. It is situated northeast of Bologna, on the Po di Volano, a branch channel of the main stream ...

, Italy. Later models used as electrolyte a film of LiI, which was doped with alumina nanoparticles to increase its conductivity. LiI was formed in an ''in situ'' chemical reaction between the Li anode and iodine-poly( 2-vinylpyridine) cathode, and therefore was self-healed from erosion and cracks during the operation. Sodium-sulfur cells, based on ceramic β-Al₂O₃ electrolyte sandwiched between molten-sodium anode and molten-sulfur cathode showed high energy densities and were considered for car batteries in the 1990s, but disregarded due to the brittleness of alumina, which resulted in cracks and critical failure due to reaction between molten sodium and sulfur. Replacement of β-Al₂O₃ with

NASICON NASICON is an acronym for sodium (Na) Super Ionic CONductor, which usually refers to a family of solids with the chemical formula Na1+xZr2SixP3−xO12, 0 < x < 3. In a broader sense, it is also used for similar compounds where Na, Zr and/or Si ...

did not save this application because it did not solve the cracking problem, and because NASICON reacted with the molten sodium.

Yttria-stabilized zirconia Yttria-stabilized zirconia (YSZ) is a ceramic in which the cubic crystal structure of zirconium dioxide is made stable at room temperature by an addition of yttrium oxide. These oxides are commonly called "zirconia" ( Zr O2) and "yttria" ( Y2 O3 ...

is used as a solid electrolyte in oxygen sensors in cars, generating voltage that depends on the ratio of oxygen and exhaust gas and providing electronic feedback to the fuel injector. Such sensors are also installed at many metallurgical and glass-making factories. Similar sensors of CO₂, chlorine and other gases based on solid silver halide electrolytes have been proposed in the 1980s–1990s. Since mid-1980s, a Li-based solid electrolyte is used to separate the

electrochromic Electrochromism is a phenomenon in which a material displays changes in color or opacity in response to an electrical stimulus. In this way, a smart window made of an electrochromic material can block specific wavelengths of ultraviolet, vis ...

film (typically WO₃) and ion-storing film (typically LiCoO₂) in the

smart glass Smart glass or switchable glass (also called a smart window or switchable window) is a glass or glazing whose light transmission properties dynamically alter to control the passage of solar irradiation into buildings. In general, the glass chan ...

, a window whose transparency is controlled by external voltage. Solid-state ionic conductors are essential components of

lithium-ion batteries A lithium-ion or Li-ion battery is a type of rechargeable battery which uses the reversible reduction of lithium ions to store energy. It is the predominant battery type used in portable consumer electronics and electric vehicles. It also se ...

proton exchange membrane fuel cell A proton is a stable subatomic particle, symbol , H+, or 1H+ with a positive electric charge of +1 ''e'' elementary charge. Its mass is slightly less than that of a neutron and 1,836 times the mass of an electron (the proton–electron mass ...

s (PEMFCs),

supercapacitor A supercapacitor (SC), also called an ultracapacitor, is a high-capacity capacitor, with a capacitance value much higher than other capacitors but with lower voltage limits. It bridges the gap between electrolytic capacitors and rechargeable ba ...

s, a novel class of electrochemical energy storage devices, and

s, devices that produces electricity from oxidizing a fuel.

Nafion Nafion is a brand name for a sulfonated tetrafluoroethylene based fluoropolymer-copolymer discovered in the late 1960s by Dr. Walther Grot of DuPont. Nafion is a brand of the Chemours company. It is the first of a class of synthetic polymers with ...

, a flexible

fluoropolymer A fluoropolymer is a fluorocarbon-based polymer with multiple carbon–fluorine bonds. It is characterized by a high resistance to solvents, acids, and bases. The best known fluoropolymer is polytetrafluoroethylene under the brand name "Teflon ...

copolymer In polymer chemistry, a copolymer is a polymer derived from more than one species of monomer. The polymerization of monomers into copolymers is called copolymerization. Copolymers obtained from the copolymerization of two monomer species are some ...

discovered in the late 1960s, is widely used as a polymer electrolyte in PEMFCs.

References

{{Reflist, 35em, refs= {{cite book , last = Chowdari , first = B. V. R. , title = Proceedings of the 9th Asian Conference on Solid State Ionics the science and technology of ions in motion: Jeju Island, South Korea, 6–11 June 2004 , publisher = World Scientific , location = Singapore River Edge, NJ , year = 2004 , isbn = 9789812702586 Faraday, M. (1839) ''Experimental Researches in Electricity'', Art. 1339, Taylor and Francis, London. {{cite book, last=O’Keeffe, first=M., year=1976, page=101, title=Superionic Conductors, editor1-last=Mahan, editor1-first=G. D., editor2-last=Roth, editor2-first=W. L., publisher=Plenum Press, location=New York, doi=10.1007/978-1-4615-8789-7_9, isbn=978-1-4615-8791-0 Nernst, W. (1926) ''Theoretische Chemie'', Enke, Stuttgart {{cite journal, author=Hittorf, J.W. , journal = Z. Phys. Chem. , volume=10 , year=1892, pages= 593 Schottky, W.; Ulich, H. and Wagner, C. (1929) ''Thermodynamik'', Springer, Berlin. {{cite journal, author1=Wagner, C. , author2=Schottky, W. , journal = Z. Phys. Chem. B , volume=11 , year=1930, pages= 163, title=Theorie der geordneten Mischphasen, trans-title=Theory of arranged mixed phases {{cite journal, author=Wagner C , year=1933 , journal = Z. Phys. Chem. B , volume=22 , pages=181–194, title=Theorie der geordneten Mischphasen. III. Felordnungserscheinungen in polaren Verbindungen als Grundlage für Ionen- und Elektronenleitung , doi=10.1515/zpch-1933-2213 , s2cid=202044725 , trans-title=Theory of arranged mixed phases. III. Disarranged phenomena in polar compounds as basis for ionic and electronic conduction {{cite journal, author1=Tubandt, C. , author2=Lorenz, E. , journal = Z. Phys. Chem. B , volume=24 , year=1914, pages= 513–543, title= Molekularzustand und elektrisches Leitvermögen kristallisierter Salze, doi=10.1515/zpch-1914-8737 , s2cid=99214772 {{cite journal, author=Arrhenius, S. , journal = Z. Phys. Chem., volume= 1, year=1887, pages= 631–648, title=Über die Dissociation der in Wasser gelösten Stoffe, doi=10.1515/zpch-1887-0164, s2cid = 102373219, url = https://zenodo.org/record/1448928 Nernst, W. (1899) pp. 192 and 367 in ''Mutter Erde'', Spemann, Berlin, vol. 2. Tubandt, C. (1932) in: ''Handbuch der Experimentalphysik XII'', part 1, W. Wien and F. Harms (eds.), Akadem. Verlagsges., Leipzig. Weber R. (1883) Berliner Akad. Wiss. II 1233 Owens B. B. (1971) ''Advances in Electrochemistry and Electrochemical Engineering''. vol 8. P. Delahay and C. W. Tobias (eds.). New York: Wiley-Interscience. p. 1. {{ISBN, 0471875260. {{cite book, last=Yamamoto, first=O., year=1995, url=https://books.google.com/books?id=o_OEVwO2ne0C, title=Solid State Electrochemistry, editor-last=Bruce, editor-first=P. G., location=Cambridge, publisher=Cambridge University Press, isbn=0521599490, page=292 {{cite book, last1=Owens, first1=B. B., last2=Oxley, first2=J. E., last3=Sammels, first3=A. F., year=1977, title=Solid Electrolytes, editor-last=Geller, editor-first=S., location=Berlin, publisher=Springer, doi=10.1007/3540083383_4, isbn=978-3-540-08338-2, pag
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url=https://archive.org/details/solidelectrolyte0021unse/page/67 Fischer W. A. and Janke D. (1975) ''Metallurgische Elektrochemie''. Berlin: Springer. Electrochemistry