What Is Barium Titanate?
Barium titanate is a synthetic inorganic compound with a perovskite structure.
It is a white solid at room temperature with a melting point of 1,625 °C and a density of 6.02 g/㎤. It is designated as a deleterious substance and as a “barium compound”.
Uses of Barium Titanate
1. Current Main Applications
Barium titanate, also called “barium titanate ceramics,” has piezoelectric and pyroelectric properties as well as dielectric properties that cause internal polarization and store electricity when voltage is applied. Ceramic capacitors are used as materials for electronic components such as ceramic capacitors, piezoelectric elements, thermistors, and varistors. Advances in MLCC technology have enabled miniaturization of devices such as cell phones.
Piezoelectric elements are electronic components that change their internal charge under physical pressure or vibrate when voltage is applied. They are used in electronic lighters and speakers.
Thermistors are electronic components that use pyroelectricity to change internal electric charge as a result of temperature changes. They are used in temperature sensors and temperature control of heaters.
2. Future Applications
There are ongoing investigations into potential future applications of barium titanate in fields such as energy storage, actuators, sensors, and biomedical devices.
Properties of Barium Titanate
1. Physical Properties
Barium titanate is a compound with the chemical formula BaTiO3 and has a high dielectric constant, high dielectric loss factor, and high refractive index. The Curie temperature (Tc) is around 130 °C. At Tc, a phase transition occurs from a paraelectric to a ferroelectric phase. Ferroelectricity is strongly affected by atomic defects and impurity mixtures.
2. Structure of Barium Titanate
The crystal structure of barium titanate changes from low to high temperatures in the order of rhombohedral, orthorhombic, tetragonal, and cubic. Of these, the tetragonal crystal at room temperature is a ferroelectric material, while the cubic crystal at high temperatures (120°C or higher) is an industrially important material as a paraelectric material.
It has a perovskite structure, with Ba ions at the vertices of the unit lattice, O ions at the face centers, and Ti ions at the body centers. Even in the absence of an electric field, barium titanate polarizes each ion slightly out of its normal position. This phenomenon is called spontaneous polarization. Since the direction of polarization is reversed by an external electric field, it is called ferroelectric. It is also called a “displacive ferroelectric” because ferroelectricity is induced by the mutation of ions.
Other Information on Barium Titanate
1. Production Method of Barium Titanate
1. Solid Phase Reaction Method
Barium carbonate and titanium oxide are wet-mixed, filtered, dried, granulated, molded, sintered, and pulverized. Barium carbonate is prepared from barium sulfide, barium chloride, barium hydroxide, etc. Care must be taken because the Curie point shifts to the low-temperature side when strontium is mixed in as an impurity.
Titanium dioxide is prepared by either the sulfuric acid method or the chlorine method. In the sulfuric acid method, titanium oxide is obtained by adding sulfuric acid to titanium ore FeTiO3 to produce TiOSO3, then adding ammonia to burn the resulting metatitanic acid (TiO(OH)2). In the chlorine method, titanium oxide is obtained by replacing the chlorine in titanium tetrachloride with oxygen.
2. Oxalate Method
The reaction of barium chloride, titanium tetrachloride, and oxalic acid yields barium titanyl oxalate (BaTiO(C2O4)2). Barium titanate is obtained by thermal decomposition. Barium titanate of high purity is synthesized industrially by this method.
3. Citric Acid Method
Barium titanate is obtained by thermal decomposition of BaTi(C6H6O7)3・6H2O, which is prepared by reacting aqueous barium citrate and titanium citrate solutions.
4. Hydrothermal Synthesis Method
Barium titanate is obtained by heating barium hydroxide and the hydrous salt of metatitanic acid (TiO(OH)2) under normal pressure. Barium titanate with a good crystal star can be obtained by processing under high temperature and high pressure.
5. Sol-Gel Method
Barium titanate is obtained by mixing barium hydroxide gel and titanium sol, then drying, sintering, and pulverizing. This method is suitable for the preparation of composite materials.
6. Alkoxide Method
Barium titanate is obtained by rapidly mixing titanium alkoxide and barium hydroxide in a jet mixer, then heating under annular flow and crystallizing the precipitate formed.