Electrical breakdown of the positive temperature coefficient of resistivity barium titanate ceramics
- PDF / 478,397 Bytes
- 7 Pages / 612 x 792 pts (letter) Page_size
- 66 Downloads / 192 Views
MATERIALS RESEARCH
Welcome
Comments
Help
Electrical breakdown of the positive temperature coefficient of resistivity barium titanate ceramics Duk-Hee Kim Department of Materials Science and Engineering, Korea Advanced Institute of Science and Technology, Daejon, Korea
Woo-Sik Um Material Analysis Laboratory, Test and Inspection Center, Korea Academy of Industrial Technology, Seoul, Korea
Ho-Gi Kim Department of Materials Science and Engineering, Korea Advanced Institute of Science and Technology, Daejon, Korea (Received 29 November 1994; accepted 24 April 1996)
Positive temperature coefficient of resistivity barium titanate ceramic is a semiconductor at room temperature, so it is self-heated under certain applied voltage, and then changes into an insulator. The electrical breakdown has been investigated with the resistance-temperature characteristics of the three samples which have different compositions. The grain size effect on the breakdown voltage also is discussed. As the applied voltage increased, the electrical breakdown was initiated when the specimen interior was heated above the temperature corresponding to the maximum resistance on the resistance-temperature curves by joule heat.
I. INTRODUCTION
The Positive Temperature Coefficient of Resistivity (PTCR) effect was first reported by Haayman et al.1 in perovskite type barium titanate ceramics containing a small amount of donors. The PTCR effect is well explained qualitatively by the Heywang model,2 later modified by Jonker.3 This explanation is based on the presence of surface acceptor states4 at the grain boundary, which cause a potential barrier as a result of the upward bending of the conduction band in the depletion region. The changes in the height, f0 , of this potential barrier account for the resistivity anomaly in donor doped BaTiO3 within Tc , T , Tmax; Tmax is the temperature corresponding to the maximum in resistivity. The potential barrier is assumed to be compensated below Tc by the charges arising from the spontaneous polarization and increases sharply above Tc due to a rapid decrease of the relative permittivity, er (Curie –Weiss law). Since Haayman and co-workers first reported the PTCR ceramics and processing characteristics in 1955, the potential applications of such materials were quickly recognized. Over the past 30 years, many studies to develop useful material characteristics have been made. From the standpoint of the practical application of barium titanate-based PTCR ceramics, problems still remain. One of these is the high breakdown voltage 2002
J. Mater. Res., Vol. 11, No. 8, Aug 1996
required for applications such as degaussers in color TV receivers and motor starters in compressors. It is well known that dielectric breakdown is one of the primary drawbacks for high dielectric materials such as BaTiO3 ceramic.5–7 The breakdown mechanism could be classified into discharge, thermal, and intrinsic breakdown. Discharges may occur in any internal voids or bubbles that are present in the specimen interior and continue until
Data Loading...
