GRAIN-BOUNDARY LAYER CERAMIC CAPACITORS BASED ON DONOR-DOPED BA(TI1-XSNX)O3

Grain boundary layer capacitors are processed from Ba(Ti1 - xSnx)O3 solid solutions (0 < × < 0.25), doped simultaneously with donor and acceptor impurities. The starting powders are prepared by the hydrothermal method. Dielectric properties of these ceramics are strongly dependent on the concentration of donor as well as acceptor dopants, the ceramic microstructure and phase contents. It is found that the 3dn configuration of acceptor impurities also influences the dielectric properties. Fine-grained (less than or equal to 3 μm) ceramics show low loss (less than 5%), low ε{lunate}r (6 × 103) and high resistivity (greater than or equal to 2.6 × 106 Ω cm), whereas, the coarse-grained (greater than 25 μm) ceramics show high loss (greater than 100%), high ε{lunate}r (8.5 × 106) and low resistivity (less than or equal to 3 × 104 Ω cm). Energy-dispersive X-ray analysis shows uniform distribution of donor and acceptor impurities in these ceramics. Phase content analysis by electron paramagnetic resonance reveals partial coexistence of ferroelectric orthorhombic and tetragonal phases along with the paraelectric cubic phase which directly convert to the rhombohedral phase. Current-voltage characteristics and the frequency effect on dielectric properties are also investigated. The insulting behaviour of the grain boundary layers is explained on the basis of the higher concentration of barium vacancies in these layers and the vibronic activation of the acceptor states in various symmetry configurations of a lattice that undergoes diffuse phase transitions. © 1990.