Barium titanate (BTO) is an

inorganic compound An inorganic compound is typically a chemical compound that lacks carbon–hydrogen bonds⁠that is, a compound that is not an organic compound. The study of inorganic compounds is a subfield of chemistry known as ''inorganic chemistry''. Inorgan ...

with

chemical formula A chemical formula is a way of presenting information about the chemical proportions of atoms that constitute a particular chemical compound or molecule, using chemical element symbols, numbers, and sometimes also other symbols, such as pare ...

BaTiO₃. It is the barium salt of metatitanic acid.

Barium Barium is a chemical element; it has symbol Ba and atomic number 56. It is the fifth element in group 2 and is a soft, silvery alkaline earth metal. Because of its high chemical reactivity, barium is never found in nature as a free element. Th ...

titanate appears white as a powder and is transparent when prepared as large crystals. It is a

ferroelectric 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 ...

, pyroelectric, and

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 ...

ceramic A ceramic is any of the various hard, brittle, heat-resistant, and corrosion-resistant materials made by shaping and then firing an inorganic, nonmetallic material, such as clay, at a high temperature. Common examples are earthenware, porcela ...

material that exhibits the photorefractive effect. It is used in

capacitor In electrical engineering, a capacitor is a device that stores electrical energy by accumulating electric charges on two closely spaced surfaces that are insulated from each other. The capacitor was originally known as the condenser, a term st ...

electromechanical Electromechanics combine processes and procedures drawn from electrical engineering and mechanical engineering. Electromechanics focus on the interaction of electrical and mechanical systems as a whole and how the two systems interact with each ...

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 nonlinear optics.

Structure

The solid exists in one of four polymorphs depending on temperature. From high to low temperature, these crystal symmetries of the four polymorphs are

cubic Cubic may refer to: Science and mathematics * Cube (algebra), "cubic" measurement * Cube, a three-dimensional solid object bounded by six square faces, facets or sides, with three meeting at each vertex ** Cubic crystal system, a crystal system w ...

tetragonal In crystallography, the tetragonal crystal system is one of the 7 crystal systems. Tetragonal crystal lattices result from stretching a cubic lattice along one of its lattice vectors, so that the Cube (geometry), cube becomes a rectangular Pri ...

orthorhombic In crystallography, the orthorhombic crystal system is one of the 7 crystal systems. Orthorhombic Lattice (group), lattices result from stretching a cubic crystal system, cubic lattice along two of its orthogonal pairs by two different factors, res ...

and

rhombohedral In geometry, a rhombohedron (also called a rhombic hexahedron or, inaccurately, a rhomboid) is a special case of a parallelepiped in which all six faces are congruent rhombus, rhombi. It can be used to define the rhombohedral lattice system, a Ho ...

crystal structure In crystallography, crystal structure is a description of ordered arrangement of atoms, ions, or molecules in a crystalline material. Ordered structures occur from intrinsic nature of constituent particles to form symmetric patterns that repeat ...

. All of these phases exhibit the

ferroelectric effect In physics and materials science, ferroelectricity is a characteristic of certain materials that have a Spontaneous process, spontaneous Polarization density, electric polarization that can be reversed by the application of an external electric f ...

apart from the cubic phase. The high temperature cubic phase is easiest to describe, as it consists of regular corner-sharing octahedral TiO₆ units that define a cube with O vertices and Ti-O-Ti edges. In the cubic phase, Ba²⁺ is located at the center of the cube, with a nominal

coordination number In chemistry, crystallography, and materials science, the coordination number, also called ligancy, of a central atom in a molecule or crystal is the number of atoms, molecules or ions bonded to it. The ion/molecule/atom surrounding the central ion ...

of 12. Lower symmetry phases are stabilized at lower temperatures and involve movement of the Ti⁴⁺ to off-center positions. The remarkable properties of this material arise from the cooperative behavior of the Ti⁴⁺ distortions. Above the melting point, the liquid has a remarkably different local structure to the solid forms, with the majority of Ti⁴⁺ coordinated to four oxygen, in tetrahedral TiO₄ units, which coexist with more highly coordinated units.

Production and handling properties

Barium titanate can be synthesized by the relatively simple sol–hydrothermal method. Barium titanate can also be manufactured by heating

barium carbonate Barium carbonate is the inorganic compound with the formula BaCO3. Like most alkaline earth metal carbonates, it is a white salt that is poorly soluble in water. It occurs as the mineral known as witherite. In a commercial sense, it is one of ...

and

titanium dioxide Titanium dioxide, also known as titanium(IV) oxide or titania , is the inorganic compound derived from titanium with the chemical formula . When used as a pigment, it is called titanium white, Pigment White 6 (PW6), or Colour Index Internationa ...

. The reaction proceeds via liquid phase sintering. Single crystals can be grown at around 1100 °C from molten

potassium fluoride Potassium fluoride is the chemical compound with the formula KF. After hydrogen fluoride, KF is the primary source of the fluoride ion for applications in manufacturing and in chemistry. It is an alkali halide salt and occurs naturally as the ...

. Other materials are often added as

dopants A dopant (also called a doping agent) is a small amount of a substance added to a material to alter its physical properties, such as electrical or optical properties. The amount of dopant is typically very low compared to the material being do ...

, e.g., Sr to form solid solutions with

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 ...

. Barium titanate reacts with

nitrogen trichloride Nitrogen trichloride, also known as trichloramine, is the chemical compound with the formula . This yellow, oily, and explosive liquid is most commonly encountered as a product of chemical reactions between ammonia-derivatives and chlorine (for ex ...

and produces a greenish or gray mixture; the

properties of the mixture are still present in this form. Much effort has been spent studying the relationship between particle morphology and its properties. Barium titanate is one of the few ceramic compounds known to exhibit

abnormal grain growth In materials science, abnormal or discontinuous grain growth, also referred to as exaggerated or secondary recrystallisation grain growth, is a grain growth phenomenon in which certain energetically favorable grains (crystallites) grow rapidly i ...

, in which large faceted grains grow in a matrix of finer grains, with profound implications on densification and physical properties. Fully dense nanocrystalline barium titanate has 40% higher

permittivity In electromagnetism, the absolute permittivity, often simply called permittivity and denoted by the Greek letter (epsilon), is a measure of the electric polarizability of a dielectric material. A material with high permittivity polarizes more ...

than the same material prepared in classic ways. The addition of inclusions of barium titanate to

tin Tin is a chemical element; it has symbol Sn () and atomic number 50. A silvery-colored metal, tin is soft enough to be cut with little force, and a bar of tin can be bent by hand with little effort. When bent, a bar of tin makes a sound, the ...

has been shown to produce a bulk material with a higher

viscoelastic In materials science and continuum mechanics, viscoelasticity is the property of materials that exhibit both Viscosity, viscous and Elasticity (physics), elastic characteristics when undergoing deformation (engineering), deformation. Viscous mate ...

stiffness Stiffness is the extent to which an object resists deformation in response to an applied force. The complementary concept is flexibility or pliability: the more flexible an object is, the less stiff it is. Calculations The stiffness, k, of a ...

than that of diamonds. Barium titanate goes through two phase transitions that change the crystal shape and volume. This phase change leads to composites where the barium titanates have a negative bulk modulus (

Young's modulus Young's modulus (or the Young modulus) is a mechanical property of solid materials that measures the tensile or compressive stiffness when the force is applied lengthwise. It is the modulus of elasticity for tension or axial compression. Youn ...

), meaning that when a force acts on the inclusions, there is displacement in the opposite direction, further stiffening the composite. Like many

oxide An oxide () is a chemical compound containing at least one oxygen atom and one other element in its chemical formula. "Oxide" itself is the dianion (anion bearing a net charge of −2) of oxygen, an O2− ion with oxygen in the oxidation st ...

s, barium titanate is insoluble in water but attacked by

sulfuric acid Sulfuric acid (American spelling and the preferred IUPAC name) or sulphuric acid (English in the Commonwealth of Nations, Commonwealth spelling), known in antiquity as oil of vitriol, is a mineral acid composed of the elements sulfur, oxygen, ...

. It is also soluble in concentrated

hydrochloric acid Hydrochloric acid, also known as muriatic acid or spirits of salt, is an aqueous solution of hydrogen chloride (HCl). It is a colorless solution with a distinctive pungency, pungent smell. It is classified as a acid strength, strong acid. It is ...

, and

hydrofluoric acid Hydrofluoric acid is a solution of hydrogen fluoride (HF) in water. Solutions of HF are colorless, acidic and highly corrosive. A common concentration is 49% (48–52%) but there are also stronger solutions (e.g. 70%) and pure HF has a boiling p ...

. Its bulk room-temperature

bandgap In solid-state physics and solid-state chemistry, a band gap, also called a bandgap or energy gap, is an energy range in a solid where no electronic states exist. In graphs of the electronic band structure of solids, the band gap refers to the ...

is 3.2 eV, but this increases to ~3.5 eV when the particle size is reduced from about 15 to 7 nm.

Uses

Barium titanate is a

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 ...

ceramic used in

s, with dielectric constant values as high as 7,000. Over a narrow temperature range, values as high as 15,000 are possible; most common ceramic and polymer materials are less than 10, while others, such as titanium dioxide (TiO₂), have values between 20 and 70. It is a

material used in

microphone 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 ...

s and other

s. The spontaneous polarization of barium titanate single crystals at room temperature range between 0.15C/m² in earlier studies, and 0.26C/m² in more recent publications, and its

Curie temperature In physics and materials science, the Curie temperature (''T''C), or Curie point, is the temperature above which certain materials lose their permanent magnetic properties, which can (in most cases) be replaced by induced magnetism. The Curie ...

is between 120 and 130 °C. The differences are related to the growth technique, with earlier flux grown crystals being less pure than current crystals grown with the

Czochralski process The Czochralski method, also Czochralski technique or Czochralski process, is a method of crystal growth used to obtain single crystals (monocrystals) of semiconductors (e.g. silicon, germanium and gallium arsenide), metals (e.g. palladium, plati ...

, which therefore have a larger spontaneous polarization and a higher Curie temperature. As a

material, it has been largely replaced by

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 ...

, also known as PZT. Polycrystalline barium titanate has a positive

temperature coefficient A temperature coefficient describes the relative change of a physical property that is associated with a given change in temperature. For a property ''R'' that changes when the temperature changes by ''dT'', the temperature coefficient α is def ...

of resistance, making it a useful material for

thermistor A thermistor is a semiconductor type of resistor in which the resistance is strongly dependent on temperature. The word ''thermistor'' is a portmanteau of ''thermal'' and ''resistor''. The varying resistance with temperature allows these devices ...

s and self-regulating electric heating systems. Barium titanate crystals find use in

nonlinear optics Nonlinear optics (NLO) is the branch of optics that describes the behaviour of light in Nonlinearity, nonlinear media, that is, media in which the polarization density P responds non-linearly to the electric field E of the light. The non-linearity ...

. The material has high beam-coupling gain, and can be operated at visible and near-infrared wavelengths. It has the highest reflectivity of the materials used for self-pumped

phase conjugation Phase conjugation is a physical transformation of a wave field where the resulting field has a reversed propagation direction but keeps its amplitudes and phases. Description It is distinguished from Time Reversal Signal Processing by the fact ...

(SPPC) applications. It can be used for continuous-wave four-wave mixing with milliwatt-range optical power. For photorefractive applications, barium titanate can be doped by various other elements, e.g.

iron Iron is a chemical element; it has symbol Fe () and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. It is, by mass, the most common element on Earth, forming much of Earth's o ...

Thin film A thin film is a layer of materials ranging from fractions of a nanometer ( monolayer) to several micrometers in thickness. The controlled synthesis of materials as thin films (a process referred to as deposition) is a fundamental step in many ...

s of barium titanate display electrooptic modulation to frequencies over 40 GHz. The pyroelectric and ferroelectric properties of barium titanate are used in some types of uncooled sensors for thermal cameras. Barium titanate is widely used in thermistors and positive temperature coefficient heating elements. For these applications, barium titanate is manufactured with

to give the material semiconductor properties. Specific applications include overcurrent protection for motors, ballasts for fluorescent lights, automobile cabin air heaters, and consumer space heaters. High-purity barium titanate powder is reported to be a key component of new barium titanate capacitor energy storage systems for use in electric vehicles. Due to their elevated

biocompatibility Biocompatibility is related to the behavior of biomaterials in various contexts. The term refers to the ability of a material to perform with an appropriate host response in a specific situation. The ambiguity of the term reflects the ongoin ...

, barium titanate

nanoparticle A nanoparticle or ultrafine particle is a particle of matter 1 to 100 nanometres (nm) in diameter. The term is sometimes used for larger particles, up to 500 nm, or fibers and tubes that are less than 100 nm in only two directions. At ...

s (BTNPs) have been recently employed as nanocarriers for

drug delivery Drug delivery involves various methods and technologies designed to transport pharmaceutical compounds to their target sites helping therapeutic effect. It involves principles related to drug preparation, route of administration, site-specif ...

. Magnetoelectric effect of giant strengths have been reported in thin films grown on barium titanate substrates.

Natural occurrence

Barioperovskite is a very rare natural analogue of BaTiO₃, found as microinclusions in benitoite.

References

External links