A complex oxide is a chemical compound that contains oxygen and at least two other elements (or oxygen and just one other element that's in at least two

oxidation states In chemistry, the oxidation state, or oxidation number, is the hypothetical charge of an atom if all of its bonds to different atoms were fully ionic. It describes the degree of oxidation (loss of electrons) of an atom in a chemical compound. Co ...

). Complex oxide materials are notable for their wide range of magnetic and electronic properties, such as

ferromagnetism Ferromagnetism is a property of certain materials (such as iron) which results in a large observed magnetic permeability, and in many cases a large magnetic coercivity allowing the material to form a permanent magnet. Ferromagnetic materials ...

ferroelectricity 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 piezoelectric and pyroelectric, with the add ...

, and

high-temperature superconductivity High-temperature superconductors (abbreviated high-c or HTS) are defined as materials that behave as superconductors at temperatures above , the boiling point of liquid nitrogen. The adjective "high temperature" is only in respect to previ ...

. These properties often come from their strongly correlated electrons in d or f orbitals.

Natural occurrence

Many

mineral In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid chemical compound with a fairly well-defined chemical composition and a specific crystal structure that occurs naturally in pure form.John P. Rafferty, ed. ( ...

s found in the ground are complex oxides. Commonly studied mineral crystal families include

spinels The spinels are any of a class of minerals of general formulation which crystallise in the cubic crystal system, cubic (isometric) crystal system, with the X anions (typically chalcogens, like oxygen and sulfur) arranged in a cubic close-packing, c ...

and

perovskites A perovskite is any material with a crystal structure following the formula ABX3, which was first discovered as the mineral called perovskite, which consists of calcium titanium oxide (CaTiO3). The mineral was first discovered in the Ural mou ...

Applications

Complex oxide materials are used in a variety of commercial applications.

Magnets

Magnet A magnet is a material or object that produces a magnetic field. This magnetic field is invisible but is responsible for the most notable property of a magnet: a force that pulls on other ferromagnetic materials, such as iron, steel, nickel, ...

s made of the complex oxide ferrite are commonly used in

transformer A transformer is a passive component that transfers electrical energy from one electrical circuit to another circuit, or multiple circuits. A varying current in any coil of the transformer produces a varying magnetic flux in the transformer' ...

cores and in

inductor An inductor, also called a coil, choke, or reactor, is a passive two-terminal electrical component that stores energy in a magnetic field when electric current flows through it. An inductor typically consists of an insulated wire wound into a c ...

s. Ferrites are ideal for these applications because they are magnetic, electrically insulating, and inexpensive.

Transducers and actuators

Piezoelectric Piezoelectricity (, ) is the electric charge that accumulates in certain solid materials—such as crystals, certain ceramics, and biological matter such as bone, DNA, and various proteins—in response to applied Stress (mechanics), mechanical s ...

transducers A transducer is a device that converts energy from one form to another. Usually a transducer converts a signal in one form of energy to a signal in another. Transducers are often employed at the boundaries of automation, measurement, and contro ...

and

actuators An actuator is a component of a machine that is responsible for moving and controlling a mechanism or system, for example by opening a valve. In simple terms, it is a "mover". An actuator requires a control device (controlled by control signal) an ...

are often made of the complex oxide PZT (

lead zirconate titanate Lead zirconate titanate is an inorganic compound with the chemical formula (0≤''x''≤1), commonly abbreviated as PZT. Also called lead zirconium titanate, it is a ceramic perovskite material that shows a marked piezoelectric effect, meaning t ...

). These transducers are used in applications such

ultrasound Ultrasound is sound waves with frequency, frequencies higher than the upper audible limit of human hearing range, hearing. Ultrasound is not different from "normal" (audible) sound in its physical properties, except that humans cannot hea ...

imaging and some

microphones A microphone, colloquially called a mic or mike (), is a transducer that converts sound into an electrical signal. Microphones are used in many applications such as telephones, hearing aids, public address systems for concert halls and public ...

. PZT is also sometimes used for

piezo ignition Piezo ignition is a type of ignition that is used in portable camping stoves, gas grills and some lighters. Piezo ignition uses the principle of piezoelectricity, which, in short, is the electric charge that accumulates in some materials in respo ...

lighter A lighter is a portable device which creates a flame, and can be used to ignite a variety of items, such as cigarettes, gas lighter, fireworks, candles or campfires. It consists of a metal or plastic container filled with a flammable liquid or c ...

s and gas grills.

Capacitors

Complex oxide materials are the dominant

dielectric In electromagnetism, a dielectric (or dielectric medium) is an electrical insulator that can be polarised by an applied electric field. When a dielectric material is placed in an electric field, electric charges do not flow through the mate ...

material in

ceramic capacitor A ceramic capacitor is a fixed-value capacitor where the ceramic material acts as the dielectric. It is constructed of two or more alternating layers of ceramic and a metal layer acting as the electrodes. The composition of the ceramic material de ...

s.
About one trillion ceramic capacitors are produced each year to be used in electronic equipment.

Fuel cells

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 often use complex oxide materials as their

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 ...

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 ...

s, and

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 ...

Gemstone jewelry

Spanish jewellery-Gold and emerald pendant at VAM-01

Many precious gemstones, such as

emerald Emerald is a gemstone and a variety of the mineral beryl (Be3Al2(SiO3)6) colored green by trace amounts of chromium or sometimes vanadium.Hurlbut, Cornelius S. Jr. and Kammerling, Robert C. (1991) ''Gemology'', John Wiley & Sons, New York, p ...

and

topaz Topaz is a silicate mineral of aluminium and fluorine with the chemical formula Al Si O( F, OH). It is used as a gemstone in jewelry and other adornments. Common topaz in its natural state is colorless, though trace element impurities can mak ...

, are complex oxide crystals. Historically, some complex oxide materials (such as

strontium titanate Strontium titanate is an oxide of strontium and titanium with the chemical formula Sr Ti O3. At room temperature, it is a centrosymmetric paraelectric material with a perovskite structure. At low temperatures it approaches a ferroelectric phase ...

yttrium aluminium garnet Yttrium aluminium garnet (YAG, Y3 Al5 O12) is a synthetic crystalline material of the garnet group. It is a cubic yttrium aluminium oxide phase, with other examples being YAlO3 (YAP) in a hexagonal or an orthorhombic, perovskite-like form, and ...

, and

gadolinium gallium garnet Gadolinium Gallium Garnet (GGG, ) is a synthetic crystalline material of the garnet group, with good mechanical, thermal, and optical properties. It is typically colorless. It has a cubic lattice, a density of 7.08 g/cm3 and its Mohs hardness is v ...

) were also synthesized as inexpensive

diamond simulant A diamond simulant, diamond imitation or imitation diamond is an object or material with gemological characteristics similar to those of a diamond. Simulants are distinct from synthetic diamonds, which are actual diamonds exhibiting the same mat ...

s, though after 1976 they were mostly eclipsed by

cubic zirconia Cubic zirconia (CZ) is the cubic crystalline form of zirconium dioxide (ZrO2). The synthesized material is hard and usually colorless, but may be made in a variety of different colors. It should not be confused with zircon, which is a zirconi ...

New electronic devices

As of 2015, there is research underway to commercialize complex oxides in new kinds of electronic devices, such as

ReRAM Resistive random-access memory (ReRAM or RRAM) is a type of non-volatile (NV) random-access (RAM) computer memory that works by changing the resistance across a dielectric solid-state material, often referred to as a memristor. ReRAM bears som ...

FeRAM Ferroelectric RAM (FeRAM, F-RAM or FRAM) is a random-access memory similar in construction to dynamic random-access memory, DRAM but using a ferroelectric layer instead of a dielectric layer to achieve non-volatility. FeRAM is one of a growing ...

, and

memristor A memristor (; a portmanteau of ''memory resistor'') is a non-linear two-terminal electrical component relating electric charge and magnetic flux linkage. It was described and named in 1971 by Leon Chua, completing a theoretical quartet of fu ...

s. Complex oxide materials are also being researched for their use in

spintronics Spintronics (a portmanteau meaning spin transport electronics), also known as spin electronics, is the study of the intrinsic spin of the electron and its associated magnetic moment, in addition to its fundamental electronic charge, in solid-sta ...

. Another potential application of complex oxide materials is superconducting power lines. A few companies have invested in pilot projects, but the technology is not widespread.

Commonly studied complex oxides

Lead zirconate titanate Lead zirconate titanate is an inorganic compound with the chemical formula (0≤''x''≤1), commonly abbreviated as PZT. Also called lead zirconium titanate, it is a ceramic perovskite material that shows a marked piezoelectric effect, meaning t ...

piezoelectric Piezoelectricity (, ) is the electric charge that accumulates in certain solid materials—such as crystals, certain ceramics, and biological matter such as bone, DNA, and various proteins—in response to applied Stress (mechanics), mechanical s ...

material) *

Lanthanum aluminate Lanthanum aluminate is an inorganic compound with the formula LaAlO3, often abbreviated as LAO. It is an optically transparent ceramic oxide with a distorted perovskite structure. Properties Crystalline LaAlO3 has a relatively high relative diel ...

(a high-dielectric insulator) *

Strontium titanate Strontium titanate is an oxide of strontium and titanium with the chemical formula Sr Ti O3. At room temperature, it is a centrosymmetric paraelectric material with a perovskite structure. At low temperatures it approaches a ferroelectric phase ...

(a high-dielectric

semiconductor A semiconductor is a material which has an electrical resistivity and conductivity, electrical conductivity value falling between that of a electrical conductor, conductor, such as copper, and an insulator (electricity), insulator, such as glas ...

) *

Lanthanum strontium manganite Lanthanum strontium manganite (LSM or LSMO) is an oxide ceramic material with the general formula La1−xSrxMnO3, where ''x'' describes the doping level. It has a Perovskite (structure), perovskite-based crystal structure, which has the general f ...

(a material exhibiting

colossal magnetoresistance Colossal magnetoresistance (CMR) is a property of some materials, mostly manganese-based perovskite oxides, that enables them to dramatically change their electrical resistance in the presence of a magnetic field. The magnetoresistance of conventio ...

) *

Barium titanate Barium titanate (BTO) is an inorganic compound with chemical formula BaTiO3. Barium titanate appears white as a powder and is transparent when prepared as large crystals. It is a Ferroelectricity, ferroelectric, Pyroelectricity, pyroelectric, and ...

multiferroic Multiferroics are defined as materials that exhibit more than one of the primary ferroic properties in the same phase: * ferromagnetism – a magnetisation that is switchable by an applied magnetic field * ferroelectricity – an electric polarisa ...

material) *

Bismuth ferrite Bismuth ferrite (BiFeO3, also commonly referred to as BFO in materials science) is an inorganic chemical compound with perovskite structure and one of the most promising multiferroic materials. The room-temperature phase of BiFeO3 is classed as ...

(a multiferroic material) *

Yttrium barium copper oxide Yttrium barium copper oxide (YBCO) is a family of crystalline chemical compounds that display high-temperature superconductivity; it includes the first material ever discovered to become superconducting above the boiling point of liquid nitrogen ...

high-temperature superconductor High-temperature superconductors (abbreviated high-c or HTS) are defined as materials that behave as superconductors at temperatures above , the boiling point of liquid nitrogen. The adjective "high temperature" is only in respect to previ ...

) *

Bismuth strontium calcium copper oxide Bismuth strontium calcium copper oxide (BSCCO, pronounced ''bisko''), is a type of cuprate superconductor having the generalized chemical formula Bi2 Sr2 Ca''n''−1 Cu''n'' O2''n''+4+''x'', with ''n'' = 2 being the most commonly stud ...

(a high-temperature superconductor)

References

{{reflist * * * *

External links

Materials science: Enter the oxides

Oxides Ferromagnetic materials Superconductivity

Natural occurrence

Applications

Magnets

Transducers and actuators

Capacitors

Fuel cells

Gemstone jewelry

New electronic devices

Commonly studied complex oxides

See also

References

External links