BaTiO3-metal composite PTC thermistors with the jump-like PTCR effect

A composite composed of a highly conducting phase and a high-resistivity BaTiO3 phase was prepared. The high-resistivity BaTiO3 was realized using a high-temperature treatment, while alloy powder was used as the conducting... [ view full abstract ]

A composite composed of a highly conducting phase and a high-resistivity BaTiO₃ phase was prepared. The high-resistivity BaTiO₃ was realized using a high-temperature treatment, while alloy powder was used as the conducting phase. The composite was prepared from a mixture of two constitutive phases: a highly conducting alloy powder and high-resistivity BaTiO₃ grains. The composition and the sintering temperature (under 1000^oC) were optimized in order to obtain a low-resistivity (less than 1 Ωcm) BaTiO₃-metal composite with a remarkable, jump-like anomaly (more than 10⁴) in the electrical resistivity at the Curie temperature of the BaTiO₃. It was postulated that the PTCR (positive temperature coefficient of the electrical resistivity) anomaly occurred exclusively as a result of the disconnection of the conducting alloy network due to the volume changes associated with the ferroelectric phase transition between the tetragonal and cubic BaTiO₃ at the Curie temperature. 

Microstructural analyses, scanning electron microscopy, x-ray powder diffraction, dilatometry and electrical measurements were used to characterize the materials that showed the jump-like PTCR  effect.