White to gray, odorless powder
5.85 g · cm -3
1620 ° C.
Insoluble in water
0.5 mg · m-3 barium
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Barium titanate is a compound oxide of barium and titanium from the group of titanates, and crystallized in the perovskite structure.
Production and representation
BaTiO3 can according to the classical mixed-oxide method from BaCO3 ( barium carbonate ) and TiO2 ( titanium dioxide) in a solid state reaction, called calcination, are produced at a temperature of 1200 ° C.
More moderate conditions provides the crystallization from a molten solution. Stoichiometric amounts of barium carbonate and titanium dioxide ( anatase) are mixed with a large excess sodium chloride. Crystallized in an oven at 1000 ° C from the barium titanate. After washing off the salt residue obtained it in a very pure form, in fine crystals.
Barium titanate belongs to the family of electrical ceramics. Barium titanate is a ferroelectric and has a pronounced hysteresis loop. All ferroelectrics as it has a high dielectric constant of about 2000. Barium crystallizes in two polymorphic types of gratings, the hexagonal lattice type and the perovskite structure. At temperatures below 120 ° C, it is present as tetragonal modification of the distorted perovskite structure, wherein the titanium ion is shifted from the oxygen ions in the z direction. This results in a dipole moment of the unit cell and polarization. At 120 ° C the phase transition is carried out to the cubic perovskite structure, wherein the titanium ion is exactly in the center of the octahedron of oxygen ions. So that the unit cell of the crystal has no dipole moment and the crystal is not ferroelectric. At high temperatures, the phase transformation takes place in the hexagonal phase. This phase change requires a more extensive rearrangement of the ions of the transition at 120 ° C. For larger crystals are therefore often happens that they break in this transformation.
Due to the ferroelectric, dielectric and pyroelectric properties of barium titanate and related perovskites such as Pb (Zr, Ti) O3 are extensively used in electronics and sensors. As example of this PTC thermistor, as well as the use as dielectric materials in capacitors, in particular ceramic capacitors may be mentioned.