Barium titanate

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Barium titanate
BaTiO3ceramics.JPG
Polycrystalline BaTiO3 in plastic
Identifiers
3D model (JSmol)
ChemSpider
ECHA InfoCard 100.031.783
EC Number
  • 234-975-0
PubChem CID
RTECS number
  • XR1437333
UNII
Properties
BaTiO3
Molar mass 233.192 g
Appearancewhite crystals
Odor odorless
Density 6.02 g/cm3, solid
Melting point 1,625 °C (2,957 °F; 1,898 K)
insoluble
Solubility slightly soluble in dilute mineral acids; dissolves in concentrated hydrofluoric acid
Band gap 3.2 eV (300 K, single crystal) [1]
no2.412; ne=2.360 [2]
Structure
Tetragonal, tP5
P4mm, No. 99
Hazards
GHS pictograms GHS-pictogram-exclam.svg
GHS Signal word Warning
H302, H332
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
X mark.svgN  verify  (what is  Yes check.svgYX mark.svgN ?)
Infobox references

Barium titanate 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 ferroelectric ceramic material that exhibits the photorefractive effect and piezoelectric properties. It is used in capacitors, electromechanical transducers and nonlinear optics.

Contents

Structure

Structure of cubic BaTiO3. The red spheres are oxide centres, blue are Ti cations, and the green spheres are Ba . Perovskite.jpg
Structure of cubic BaTiO3. The red spheres are oxide centres, blue are Ti cations, and the green spheres are Ba .

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, tetragonal, orthorhombic, and rhombohedral crystal structure. All of these phases exhibit the ferroelectric effect 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 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. [3]

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. [4]

Production and handling properties

Scanning Electron Microscopy (SEM) images showing particles of BaTiO3. The different morphologies depend on the synthesis conditions (precipitation, hydrothermal and solvothermal synthesis): size and shape can be varied by changing the concentration of precursors, the reaction temperature and the time. Color (if added) helps to emphasize the grayscale levels. In general, the synthesis of Barium titanate by precipitation from aqueous solution allows to produce particles with spherical shape with size that can be tailored from a few nanometers to several hundred nanometers by decreasing the concentration of reactants. At very low concentration the particles have the tendency to develop a dendritic-like morphology, as reported in the images. Oxides particles.jpg
Scanning Electron Microscopy (SEM) images showing particles of BaTiO3. The different morphologies depend on the synthesis conditions (precipitation, hydrothermal and solvothermal synthesis): size and shape can be varied by changing the concentration of precursors, the reaction temperature and the time. Color (if added) helps to emphasize the grayscale levels. In general, the synthesis of Barium titanate by precipitation from aqueous solution allows to produce particles with spherical shape with size that can be tailored from a few nanometers to several hundred nanometers by decreasing the concentration of reactants. At very low concentration the particles have the tendency to develop a dendritic-like morphology, as reported in the images.

Barium titanate can be synthesized by the relatively simple sol–hydrothermal method. [5] Barium titanate can also be manufactured by heating barium carbonate and titanium dioxide. The reaction proceeds via liquid phase sintering. Single crystals can be grown at around 1100 °C from molten potassium fluoride. [6] Other materials are often added as dopants, e.g., Sr to giveform solid solutions with strontium titanate. It reacts with nitrogen trichloride and produces a greenish or gray mixture; the ferroelectric properties of the mixture are still present in this form.

Much effort has been spent studying the relationship between particle morphology and its properties. Fully dense nanocrystalline barium titanate has 40% higher permittivity than the same material prepared in classic ways. [7] The addition of inclusions of barium titanate to tin has been shown to produce a bulk material with a higher viscoelastic stiffness 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), meaning that when a force acts on the inclusions, there is displacement in the opposite direction, further stiffening the composite. [8]

Like many oxides, barium titanate is insoluble in water but attacked by sulfuric acid. Its bulk room-temperature bandgap is 3.2 eV, but this increases to ~3.5 eV when the particle size is reduced from about 15 to 7 nm. [1]

Uses

Scanning transmission electron microscopy of the ferroelastic domains that form in BaTiO3 on cooling through the Curie temperature. The vertex point, where domain bundles meet, moves from the center in isometric crystals (top) to off-center in oblongs (bottom). BaTiO3 ferro domains.jpg
Scanning transmission electron microscopy of the ferroelastic domains that form in BaTiO3 on cooling through the Curie temperature. The vertex point, where domain bundles meet, moves from the center in isometric crystals (top) to off-center in oblongs (bottom).

Barium titanate is a dielectric ceramic used in capacitors, 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. [10]

It is a piezoelectric material used in microphones and other transducers. The spontaneous polarization of barium titanate single crystals at room temperature range between 0.15 C/m2 in earlier studies, [11] and 0.26 C/m2 in more recent publications, [12] and its Curie temperature 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, [13] which therefore have a larger spontaneous polarization and a higher Curie temperature.

As a piezoelectric material, it has been largely replaced by lead zirconate titanate, also known as PZT. Polycrystalline barium titanate has a positive temperature coefficient of resistance, making it a useful material for thermistors and self-regulating electric heating systems.

Barium titanate crystals find use in nonlinear optics. 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 (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. [14]

Thin films of barium titanate display electrooptic modulation to frequencies over 40 GHz. [15]

The pyroelectric and ferroelectric properties of barium titanate are used in some types of uncooled sensors for thermal cameras.

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. [16]

Due to their elevated biocompatibility, barium titanate nanoparticles (BTNPs) have been recently employed as nanocarriers for drug delivery. [17]

Magnetoelectric effect of giant strengths have been reported in thin films grown on barium titanate substrates. [18] [19]

Natural occurrence

Barioperovskite is a very rare natural analogue of BaTiO3, found as microinclusions in benitoite. [20]

See also

Related Research Articles

Piezoelectricity electric charge that accumulates in certain solid materials in response to applied mechanical stress

Piezoelectricity is the electric charge that accumulates in certain solid materials in response to applied mechanical stress. The word piezoelectricity means electricity resulting from pressure and latent heat. It is derived from the Greek word πιέζειν; piezein, which means to squeeze or press, and ἤλεκτρον ēlektron, which means amber, an ancient source of electric charge. French physicists Jacques and Pierre Curie discovered piezoelectricity in 1880.

Dielectric Electrically poorly conducting or non-conducting, non-metallic substance of which charge carriers are generally not free to move

A dielectric is an electrical insulator that can be polarized by an applied electric field. When a dielectric material is placed in an electric field, electric charges do not flow through the material as they do in an electrical conductor but only slightly shift from their average equilibrium positions causing dielectric polarization. Because of dielectric polarization, positive charges are displaced in the direction of the field and negative charges shift in the direction opposite to the field. This creates an internal electric field that reduces the overall field within the dielectric itself. If a dielectric is composed of weakly bonded molecules, those molecules not only become polarized, but also reorient so that their symmetry axes align to the field.

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 pyroelectric, with the additional property that their natural electrical polarization is reversible. The term is used in analogy to ferromagnetism, in which a material exhibits a permanent magnetic moment. Ferromagnetism was already known when ferroelectricity was discovered in 1920 in Rochelle salt by Valasek. Thus, the prefix ferro, meaning iron, was used to describe the property despite the fact that most ferroelectric materials do not contain iron. Materials that are both ferroelectric and ferromagnetic are known as multiferroics.

Strontium titanate chemical compound

Strontium titanate is an oxide of strontium and titanium with the chemical formula SrTiO3. At room temperature, it is a centrosymmetric paraelectric material with a perovskite structure. At low temperatures it approaches a ferroelectric phase transition with a very large dielectric constant ~104 but remains paraelectric down to the lowest temperatures measured as a result of quantum fluctuations, making it a quantum paraelectric. It was long thought to be a wholly artificial material, until 1982 when its natural counterpart—discovered in Siberia and named tausonite—was recognised by the IMA. Tausonite remains an extremely rare mineral in nature, occurring as very tiny crystals. Its most important application has been in its synthesized form wherein it is occasionally encountered as a diamond simulant, in precision optics, in varistors, and in advanced ceramics.

Lead zirconate titanate intermetallic inorganic chemical compound

Lead zirconate titanate is an inorganic compound with the chemical formula Pb[ZrxTi1−x]O3 (0≤x≤1). Also called lead zirconium titanate, it is a ceramic perovskite material that shows a marked piezoelectric effect, meaning that the compound changes shape when an electric field is applied. It is used in a number of practical applications such as ultrasonic transducers and piezoelectric resonators. It is a white to off-white solid.

Electroceramics is a class of ceramic materials used primarily for their electrical properties.

Multiferroics are defined as materials that exhibit more than one of the primary ferroic properties in the same phase:

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 rhombohedral belonging to the space group R3c. It is synthesized in bulk and thin film form and both its antiferromagnetic (G type ordering) Néel temperature (approximately 653 K ) and ferroelectric Curie temperature are well above room temperature (approximately 1100K). Ferroelectric polarization occurs along the pseudocubic direction ( ) with a magnitude of 90–95 μC/cm2.

The Burns temperature, Td, is the temperature where a ferroelectric material, previously in paraelectric state, starts to present randomly polarized nanoregions, that are polar precursor cluster. This behaviour is typical of several, but not all, ferroelectric materials, and was observed in lead titanate (PbTiO3), potassium niobate (KNbO3), lead lanthanum zirconate titanate (PLZT), lead magnesium niobate (PMN), lead zinc niobate (PZN), K2Sr4(NbO3)10, and strontium barium niobate (SBN), Na1/2Bi1/2O3(NBT).

Barium borate is an inorganic compound, a borate of barium with a chemical formula BaB2O4 or Ba(BO2)2. It is available as a hydrate or dehydrated form, as white powder or colorless crystals. The crystals exist in the high-temperature α phase and low-temperature β phase, abbreviated as BBO; both phases are birefringent, and BBO is a common nonlinear optical material.

Lead titanate chemical compound

Lead(II) titanate is an inorganic compound with the chemical formula PbTiO3. It is the lead salt of titanic acid. Lead(II) titanate is a yellow powder that is insoluble in water.

In its most general form, the magnetoelectric effect (ME) denotes any coupling between the magnetic and the electric properties of a material. The first example of such an effect was described by Wilhelm Röntgen in 1888, who found that a dielectric material moving through an electric field would become magnetized. A material where such a coupling is intrinsically present is called a magnetoelectric.

Ferroelectric ceramics is a special group of minerals that have ferroelectric properties: the strong dependence of the dielectric constant of temperature, electrical field, the presence of hysteresis and others.

Barium orthotitanate is the inorganic compound with the chemical formula Ba2TiO4. It is a colourless solid that is of interest because of its relationship to barium titanate, a useful electroceramic.

Abnormal grain growth

Abnormal or discontinuous grain growth, also referred to as exaggerated or secondary recrystallisation grain growth, is a grain growth phenomenon through which certain energetically favorable grains (crystallites) grow rapidly in a matrix of finer grains resulting in a bimodal grain size distribution.

Relaxor ferroelectrics are ferroelectric materials that exhibit high electrostriction. As of 2015, although they have been studied for over fifty years, the mechanism for this effect is still not completely understood, and is the subject of continuing research.

A complex oxide is a chemical compound that contains oxygen and at least two other elements. Complex oxide materials are notable for their wide range of magnetic and electronic properties, such as ferromagnetism, ferroelectricity, and high-temperature superconductivity. These properties often come from their strongly correlated electrons in d or f orbitals.

Sodium bismuth titanate or bismuth sodium titanium oxide (NBT or BNT) is a solid inorganic compound of sodium, bismuth, titanium and oxygen with the chemical formula of Na0.5Bi0.5TiO3 or Bi0.5Na0.5TiO3. This compound adopts the perovskite structure.

A polar metal, metallic ferroelectric, or ferroelectric metal is a metal that contains an electric dipole moment. Its components have an ordered electric dipole. Such metals should be unexpected, because the charge should conduct by way of the free electrons in the metal and neutralize the polarized charge. However they do exist. Probably the first report of a polar metal was in single crystals of the cuprate superconductors YBa2Cu3O7-δ,. A polarization was observed along one (001) axis by pyroelectric effect measurements, and the sign of the polarization was shown to be reversible, while its magnitude could be increased by poling by an electric field. The polarization was found to disappear in the superconducting state. The lattice distortions responsible were considered to be a result of oxygen ion displacements induced by doped charges that break inversion symmetry. The effect was utilized for fabrication of pyroelectric detectors for space applications, having the advantage of large pyroelectric coefficient and low intrinsic resistance. Another substance family that can produce a polar metal is the nickelate perovskites. One example interpreted to show polar metallic behavior is lanthanum nickelate, LaNiO3. A thin film of LaNiO3 grown on the (111) crystal face of lanthanum aluminate, (LaAlO3) was interpreted to be both conductor and a polar material at room temperature. The resistivity of this system, however, shows an upturn with decreasing temperature, hence does not strictly adhere to the definition of a metal. Also, when grown 3 or 4 unit cells thick (1-2 nm) on the (100) crystal face of LaAlO3, the LaNiO3 can be a polar insulator or polar metal depending on the atomic termination of the surface. Lithium osmate, LiOsO3 also undergoes a ferrorelectric transition when it is cooled below 140K. The point group changes from R3c to R3c losing its centrosymmetry. At room temperature and below, lithium osmate is an electric conductor, in single crystal, polycrystalline or powder forms, and the ferroelectric form only appears below 140K. Above 140K the material behaves like a normal metal.

References

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