TEMPERATURE-STABLE DIELECTRIC MATERIALS IN THE SYSTEM BATIO3-NB2O5-CO3O4

Incorporation of Nb and Co and formation of dielectric ceramics were studied in ceramics of the system BaTiO3-Nb2O5-Co3O4. Temperature-stable dielectric materials of the specification 'X7R' were found showing permittivities up to K congruent to 4800. The slow volume diffusion of Nb favours the formation of 'core-shell' structures in BaTiO3 which are responsible for the temperature-stability. Pentavalent Nb and divalent Co show a pronounced cosolubility in BaTiO3. At the atomic ratio Nb:Co=2:1 semiconductive materials occur which show the PTCR effect. The ratio of Nb:Co=2:1 strongly suggests charge compensation of [Nb5+]-donors by [Co2+]''-acceptors on Ti sites, forming the complex [Nb2/35+Co1/32+](4+). The insulation resistance and life stability of thin dielectric layers of BaTiO3-Nb,Co X7R material ave determined by the inter connection of lower insulating undoped BaTiO3 cores. The percolation limit depends on the dispersal of Nb2O5 and Co3O4 over the BaTiO3.