Barium titanate is a compound of barium oxides and titanium BaTiO 3 . Barium salt of metatitanic acid , which does not exist in its free form, is H 2 TiO 3 . A crystalline modification of barium titanate with a perovskite structure is a ferroelectric with a photorefractive and piezoelectric effect . After the discovery of B. Vul in 1944 of the ferroelectric properties of barium titanate, a fundamentally new stage began in the study of ferroelectrics.
| Barium titanate | |
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| Systematic name | Barium titanate |
| Chem. formula | BaTiO 3 |
| Physical properties | |
| Molar mass | 233.192 g / mol |
| Density | 6.02 g / cm³ |
| Thermal properties | |
| T. melt. | 1616 ° C |
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Content
Physical Properties
Barium titanate is a colorless crystals . Insoluble in water.
As the temperature decreases, barium titanate crystals undergo a series of consecutive ferroelectric phase transitions: at 120 ° C they transfer from the cubic (paraelectric) phase with the Pm3m space group to the tetragonal polar (ferroelectric) phase with the space group P4mm, then at 5 ° C there is a transition to the orthorhombic polar phase with the space group Amm2 and, finally, at −90 ° C, into the rhombohedral polar phase with the space group R3m. All three transitions are transitions of the first kind, so that with a change in temperature, the dielectric constant changes abruptly. Above the temperature T c = 120 ° C, the dielectric constant follows the Curie-Weiss law: Where
- - the dielectric constant,
- C is the Curie constant , depending on the substance, (2900 for BaTiO 3 ).
- T is the absolute temperature in kelvins ,
- T c - Curie temperature , K.
- C is the Curie constant , depending on the substance, (2900 for BaTiO 3 ).
Barium titanate is characterized by high dielectric constant values (up to 10 4 ; 1400 ± 250 at NU); Based on it, several types of ferroelectric ceramics have been developed, used to create capacitors, piezoelectric sensors, posistor.
In addition to the cubic modification with the perovskite structure, a hexagonal modification of barium titanate (sp. Gr. P6 3 / mmc) is known, which is stable at temperatures above 1430 ° C.
Getting
Barium titanate is obtained by sintering BaCO 3 with TiO 2 at 1100 ° C:
BaCO 3 + TiO 2 = BaTiO 3 + CO 2 .
For growing single crystals, a solution of BaCO 3 and TiO 2 in KF or BaCl 2 melts is used .
There is also a peroxide method:
TiCl 4 + BaCl 2 + 2H 2 O 2 + 6NH 4 OH = BaO 2 O 2 TiO • 2H 2 O ↓ + 6NH 4 Cl + 3H 2 O
BaO 2 O 2 TiO • 2H 2 O = BaTiO 3 + O 2 ↑ (decomposition at 700 ° C)
Barium titanate can also be obtained by decomposition of barium titanyl oxalate Ba (TiO) (C 2 O 4 ) 2 .
Application
Barium titanate is used as a dielectric in the manufacture of ceramic capacitors , as well as a material for piezoelectric microphones and piezoelectric emitters .
Literature
- Vul B. M. DAN SSSR, vol. 43, p. 308 (1944).
- Fesenko EG. Perovskite family and ferroelectricity. M .: Atomizdat , 1972.
- Venevtsev Yu.N., Politova E.D., Ivanov S.A. Ferro and antiferroelectrics of the barium titanate family. M .: Chemistry , 1985.
- Lines M., Glass A. Ferroelectric and related materials. M .: Mir , 1981.