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 state In chemistry, the oxidation state, or oxidation number, is the hypothetical Electrical charge, charge of an atom if all of its Chemical bond, bonds to other atoms are fully Ionic bond, ionic. It describes the degree of oxidation (loss of electrons ...

s). 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) that results in a significant, observable magnetic permeability, and in many cases, a significant magnetic coercivity, allowing the material to form a permanent magnet. Ferromagne ...

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 ...

, and

high-temperature superconductivity High-temperature superconductivity (high-c or HTS) is superconductivity in materials with a critical temperature (the temperature below which the material behaves as a superconductor) above , the boiling point of liquid nitrogen. They are "high- ...

. 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 substance with a fairly well-defined chemical composition and a specific crystal structure that occurs naturally in pure form.John P. Rafferty, ed. (2011): Mi ...

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

perovskites A perovskite is a crystalline material of formula ABX3 with a crystal structure similar to that of Perovskite, the mineral perovskite, this latter consisting of calcium titanium oxide (CaTiO3). The mineral was first discovered in the Ural Moun ...

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

cores and in

inductor An inductor, also called a coil, choke, or reactor, is a Passivity (engineering), passive two-terminal electronic component, electrical component that stores energy in a magnetic field when an electric current flows through it. An inductor typic ...

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 ...

transducer A transducer is a device that Energy transformation, 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, M ...

s and

actuator An actuator is a machine element, component of a machine that produces force, torque, or Displacement (geometry), displacement, when an electrical, Pneumatics, pneumatic or Hydraulic fluid, hydraulic input is supplied to it in a system (called an ...

s are often made of the complex oxide PZT (

lead zirconate titanate Lead zirconate titanate, also called lead zirconium titanate and commonly abbreviated as PZT, is an inorganic compound with the chemical formula . It is a ceramic perovskite material that shows a marked piezoelectric effect, meaning that the comp ...

). These transducers are used in applications such

ultrasound Ultrasound is sound with frequency, frequencies greater than 20 Hertz, kilohertz. This frequency is the approximate upper audible hearing range, limit of human hearing in healthy young adults. The physical principles of acoustic waves apply ...

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 publi ...

. 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 is the electric charge that accumulates in some materials in response to m ...

lighter A lighter is a portable device which uses mechanical or electrical means to create a controlled flame, and can be used to ignite a variety of flammable items, such as cigarettes, butane gas, fireworks, candles, or campfires. A lighter typic ...

s and gas grills.

Capacitors

Complex oxide materials are the dominant

dielectric In electromagnetism, a dielectric (or dielectric medium) is an Insulator (electricity), electrical insulator that can be Polarisability, polarised by an applied electric field. When a dielectric material is placed in an electric field, electric ...

material in ceramic capacitors.
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 Electrochemistry, 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 cera ...

s often use complex oxide materials as their

electrolyte An electrolyte is a substance that conducts electricity through the movement of ions, but not through the movement of electrons. This includes most soluble Salt (chemistry), salts, acids, and Base (chemistry), bases, dissolved in a polar solven ...

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

s, and

cathode A cathode is the electrode from which a conventional current leaves a polarized electrical device such as a lead-acid battery. This definition can be recalled by using the mnemonic ''CCD'' for ''Cathode Current Departs''. Conventional curren ...

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 ...

and

topaz Topaz is a silicate mineral made of aluminium, aluminum and fluorine with the chemical formula aluminium, Alsilicon, Sioxygen, O(fluorine, F, hydroxide, OH). It is used as a gemstone in jewelry and other adornments. Common topaz in its natural ...

, 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 strontium, Srtitanium, Tioxygen, O3. At room temperature, it is a centrosymmetric paraelectricity, paraelectric material with a Perovskite (structure), perovskite st ...

yttrium aluminium garnet Yttrium aluminium garnet (YAG, Yttrium, Y3Aluminium, Al5Oxygen, O12) is a synthetic crystalline material of the garnet group. It is a Crystal system, cubic yttrium aluminium oxide phase, with other examples being YAlO3 (YAP) in a Crystal system, ...

, and gadolinium gallium garnet) were also synthesized as inexpensive

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

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 zirc ...

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 memory, random-access (RAM) computer memory that works by changing the resistance across a dielectric solid-state material, often referred to as a memrist ...

, FeRAM, 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 ...

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-st ...

. 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

Barium titanate Barium titanate (BTO) is an inorganic compound with chemical formula BaTiO3. It is the barium salt of metatitanic acid. Barium titanate appears white as a powder and is transparent when prepared as large crystals. It is a Ferroelectricity, ferroe ...

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 polari ...

material) * Bismuth ferrite (a multiferroic material) * Bismuth strontium calcium copper oxide (a high-temperature superconductor) *

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 die ...

(a high-dielectric insulator) * Lanthanum strontium manganite (a material exhibiting colossal magnetoresistance) *

Lead zirconate titanate Lead zirconate titanate, also called lead zirconium titanate and commonly abbreviated as PZT, is an inorganic compound with the chemical formula . It is a ceramic perovskite material that shows a marked piezoelectric effect, meaning that the comp ...

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) *

Strontium titanate Strontium titanate is an oxide of strontium and titanium with the chemical formula strontium, Srtitanium, Tioxygen, O3. At room temperature, it is a centrosymmetric paraelectricity, paraelectric material with a Perovskite (structure), perovskite st ...

(a high-dielectric

semiconductor A semiconductor is a material with electrical conductivity between that of a conductor and an insulator. Its conductivity can be modified by adding impurities (" doping") to its crystal structure. When two regions with different doping level ...

) *

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 superconductivity (high-c or HTS) is superconductivity in materials with a critical temperature (the temperature below which the material behaves as a superconductor) above , the boiling point of liquid nitrogen. They are "high- ...

)

References

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External links

Materials science: Enter the oxides
Nature. (subscription required)
Condensed-matter physics: Complex oxides on fire

Complex oxides: A tale of two enemies

Oxide interfaces
Ferromagnetic materials Superconductivity