Low temperature conductive ceramic material - based on barium-titanate is made of vary small grain size to improve breakdown voltage and homogeneity

摘要

The ceramic material consists of a Ba/Ca-mixed titanate with fine grains. The grains consist of a core of Ba-rich and a shell of Ca-rich titanate. The material is prepared by addition of CaCO3, pref. 15-30 mole.%, to the doped Ba-titanate and using standard ceramic processing. The mixed materials are calcinated at 800-1200 deg.C and sintered at a temp. in the range 1250-1450 deg.C. The proportions of the elements Ba, Ca, Sr and Pb to that of Ti are related as follows: (Ba+Ca+Sr+Pb)/Ti = 1. Sr and Pb are added to affect the transition temp. USE/ADVANTAGE - During calcination Ca-rich and Ba-rich titanates are formed alongsidem each other. During sintering the Ba-rich phases act as crystallisation seeds by building a Ca-rich shell around them. This process allows many seeds to be formed, which keeps the grainsize low, e.g. 5 +/- 2 micron. The process is used to mfr. material for low resistance PTC-resistors with a high breakdown voltage.