NOVEL DOPING MECHANISM FOR VERY-HIGH-PERMITTIVITY BARIUM-TITANATE CERAMICS

Barium titanate (BaTiO3) can be doped with La3+ ions via partial subst itution for Ba2+ ions; charge balance Is maintained by the creation of Ti4+ vacancies. Samples processed in an atmosphere of 1 bar O-2 and a temperature of 1350 degrees C are insulating and free from electronic defects associated with either O-2 loss or reduction of Ti4+ to Ti3+. The Curie temperature (T-c)decreases approximately linearly as the la nthanum content increases and, at the same time, an increase in the pe rmittivity (epsilon') maximum at T-c occurs. For the composition Ba1-x LaxTi1-x/4O3, where x = 0.05, epsilon' has a maximum value of 19000 at 18 degrees C, compared with a typical value of 10000 at 130 degrees C in undoped BaTiO3 ceramics. This value is the highest value reported for A-site-doped BaTiO3 and is linked to the mechanism of combined A-s ite doping and Ti-vacancy creation.