PTC (positive temperature coefficient) thermistors based on BaTiO3 semiconducting ceramics are important devices for ferroelectric materials.
Due to their great temperature coefficient of resistance, barium titanate and its related compounds are ideal candidates for producing various PTC components. Particularly, Ba1-xSrxTiO3(x=0~1) ceramic material-based PTC thermistors have nonlinear characteristics around the Curie point, which can be enhanced by the addition of some minor impurities such as Cu and Mn.
Jo Myong Chol, a researcher at the Institute of Semiconductor, has investigated the effects of Mn addition on the dielectric properties and microstructure formation of BaTiO3-based ceramic chips and the effects of heating rate on PTCR response of barium-strontium titanate (BST) ceramics doped with Mn dopants.
Mn addition works as a sintering agent, which influences the densification behavior of the overall ceramic material. The dielectric constant increases to as high as 5 800 (at 25℃) and the dielectric loss decreases by 1% when Mn-content is added properly. This shows that the phase formation, density, microstructure and electrical properties of co-doped BST ceramics containing sintering additives are strongly affected by heating rate.
The highest densification during sintering occurs at the heating rate of 5 or 20℃/min. There is a general trend of decrease in effective resistivity with increasing heating rate, which could be attributed to the decrease in grain size. However, when the heating rate went from 5 to 20℃/min, there was a slight increase in resistivity, which may have been due to the increased proportion of crystallized secondary phases in the most rapidly heated sample, but the reasons for this are uncertain. Thus, it can be concluded that 3 and 5℃/min are the best heating rates for favorable PTCR effects.