PTCR effect in donor doped barium titanate: review of compositions, microstructures, processing and properties

Abstract

Abstract

Barium titanate is widely used in the fabrication of thermistors with a positive temperature coefficient of resistivity (PTCR). The resistivity can increase by several orders of magnitude near the phase transition temperature T_c for the ferroelectric tetragonal to the paraelectric cubic phase transformation. There is general agreement that the anomaly in the change of electrical resistivity of donor doped BaTiO₃ around T_c is due to the grain boundary effect. The Heywang–Jonker model and other mechanisms involving the nature of the electrical barrier formed across the grain boundaries of polycrystalline BaTiO₃ are reviewed. The compositional effect on BaTiO₃ based PTCR properties is listed and discussed. The influences of manufacturing methods under different stages including the initial doping methods, sample forming methods and final heat treatments on PTCR properties are compared. The complex interrelationships between compositions, microstructures, processing and PTCR characteristics are well discussed.

Keywords:

• Positive temperature coefficient of resistivity
• Barium titanate
• Composition
• Microstructure