PTCR-Ceramics Obtained Of Barium Titanate Powders With Different Crystallinity

The barium titanate powders having average crystallite sizes of 60 to 2000 nm have been prepared by calcination of barium titanyl oxalate (BTO) at temperatures of 700 divide1150degC. Morphology, recrystallization kinetics and crystalline structure of the barium titanate powders have been studied using the SEM and X-ray methods. The PTCR ceramics of (BaCaPb)TiO₃ compound have been produced by using oxalate-derived barium titanate powders. Microstructure and electrical properties of the PTCR samples have been investigated. The increase of the crystallinity of starting powders decreases the ceramic grain sizes, promotes resistivity growth and significantly influences on the resistivity jump and breakdown electric intensity of the ceramics. The optimal BTO heat treatment range providing maximum breakdown electric intensity of the PTCR devices having equal resistance of 31 Omega has been found. This temperature range corresponded to the barium titanate powder sizes of ~200 nm. The breakdown electric intensity and resistivity jump of so prepared samples are more affected by density of electron traps forming the double Schottky barrier at cooling than its microstructure. The impedance spectroscopy data testifies to inhomogeneities of the grain boundary potential barriers appearing when the treatment temperature of BTO deviates from the optimum.