Бария титанат(IV)

Описание

Attributing to its ferroelectricity, barium titanate is applied as a semiconductor with positive temperature coefficient of resistivity. It is one of the most important electroceramic materials among all the ferroelectric materials. Barium titanate has also dielectric properties, which can be used in the manufacture of ceramic capacitors. Furthermore, barium titanate has piezoelectric property and can be used in electrical devices such as actuators, accelerators, ultrasonic generators, piezoelectric transducers, filters, and sensors.

Химические свойства

White crystalline solid; exists in five crystal modifications; the common tetragonal form has a Curie point of 120°C; exhibits ferroelectric and piezoelectric properties; density 6.02 g/cm3; melts at 1,625°C; insoluble in water and alkalies; slightly soluble in dilute mineral acids; dissolves in concentrated sulfuric acid and hydrofluoric acid.

Физические свойства

White crystalline solid; exists in five crystal modifications; the common 94 BARIUM TITANATE tetragonal form has a Curie point of 120°C; exhibits ferroelectric and piezoelectric properties; density 6.02 g/cm3; melts at 1,625°C; insoluble in water and alkalies; slightly soluble in dilute mineral acids; dissolves in concentrated sulfuric acid and hydrofluoric acid.

Физические свойства

Energy Gap:
Eg=3:38 eV(E//c); 3:27 eV(E⊥c).
The energy gap decreases by -4.5×10-4 eV/℃ when the crystal structure becomes cubic at high temperature.
Dielectric Constants:
Saturated Polarizability: 78,000 esu, Dipole Moment: 5×10^-18 esu cm^-3 .

Использование

Barium titanate has many important commercial applications. It has both ferroelectric and piezoelectric properties. Also, it has a very high dielectric constant (about 1,000 times that of water). The compound has five crystalline modifications, each of which is stable over a particular temperature range. Ceramic bodies of barium titanate find wide applications in dielectric amplifiers, magnetic amplifiers, and capacitors. These storage devices are used in digital calculators, radio and television sets, ultrasonic apparatus, crystal microphone and telephone, sonar equipment, and many other electronic devices.

Подготовка

Barium titanate is made by sintering a finely powdered mixture of barium carbonate and titanium dioxide in a furnace at 1,350°C. The calcined mass is finely ground and mixed with a binder (plastic). The mixture is subjected to extrusion, pressing or film casting to obtain ceramic bodies of desired shapes. Plastic is burnt off by heating and the shaped body is sintered by firing and then polished.
Barium titanate also may be prepared by other methods. These include ignition of barium and titanium alcoholates in an organic solvent; treatment of tetraethyl titanate or other alkyl ester of titanium with an aqueous solution of barium hydroxide; and ignition of barium titanyloxalate.

Общее описание

Barium titanate(IV) is a ceramic material that can be synthesized by reacting titanium oxide (TiO₂) and barium salts in the presence of oleic acid as a stabilizing agent. It has a cubic crystal structure which allows it to have ferroelectric, thermoelectric and piezoelectric properties. It forms a film with intense photoluminescence which can be used for a wide range of electronic applications.

Структура и конформация

The space lattice of BaTiO 3 takes four types of crystal systems, depending on temperatures. The trigonal crystal (lower than -90℃) shows the spontaneous polarization to the [111] direction.The rhombic crystal (-70℃ to 5℃) shows the spontaneous polarization to the [011] direction and takes a longer structure along the direction. The tetragonal crystal (5℃–120℃) shows the spontaneous polarization to the [001] direction and takes a longer structure along the direction by the ratio of c/a=1.01. The cubic crystal (higher temperature than Curie point 120℃) takes the calcium titanate structure (Perovskite structure) and Ba atoms position at the eight corners of the cube, six O atoms at the center of the planes, and a Ti atom at the center of the body.

использованная литература

[1] Burcu Ertu?, The Overview of The Electrical Properties of Barium Titanate, American Journal of Engineering Research, 2013, vol. 02, 01-07
[2] G. Arlt, D. Hennings and G. de With, Dielectric properties of fine‐grained barium titanate ceramics, Journal of Applied Physics, 1985, vol. 58, 1619
[3] Tomoaki Karaki, Kang Yan and Masatoshi Adachi, Barium Titanate Piezoelectric Ceramics Manufactured by Two-Step Sintering, Japanese Journal of Applied Physics, 2007, vol. 46, 7035-7038