Breviary Technical Ceramics


      Werkstoffe der technischen Keramik

 Barium Titanate

Barium titanates are amongst the materials used as functional ceramics. They possess extremely high permittivities, therefore finding application as capacitor dielectrics. They are also used as piezoelectric ceramic materials.

Barium carbonate, titanium dioxide and other raw materials for doping purposes are sintered at between 1,200°C and 1,400°C to form polycrystalline barium titanate. This exhibits semiconducting properties together with a positive temperature coefficient of the ohmic resistance, for which reason it is used as a positive temperature coefficient resistor (PTC). This effect is characterised by a very sharp rise of electrical resistance – several powers of ten – starting at a reference temperature (Tb).

Figure 19: Resistance curves of PTC ceramic

PTC ceramics are used as temperature sensors in instrumentation and control technology, and as limit sensors for motor and machine protection. The material is also applied for self-regulating heating elements operating from low and mains voltage, as switching delay elements (for electric motor starting and de-magnetisation), and for overload protection.

Figure 20: Components manufactured from PTC ceramics